|
1
|
Mohammad Asghari M, Rassoli A, Mehmanparast H. Effects of self-expandable pedicle screws with shape memory alloy structures on spinal fixation strength: A finite element study. Proc Inst Mech Eng H 2025; 239:29-36. [PMID: 39579020 DOI: 10.1177/09544119241298535] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2024]
Abstract
In many spine surgeries, pedicle screws are commonly used to stabilize vertebrae, however, loosening can be a complication. Different designs have shown improvements in fixation strength, with self-expandable screws featuring shape memory alloy (SMA) structures being of particular interest. This study aimed to assess the fixation strength of self-expandable pedicle screws made with SMA (specifically Nickel-Titanium) sheets. Three types of screws were evaluated: self-expandable screws with a smooth SMA surface, self-expandable screws with a porous SMA surface, and standard design screws. Each screw underwent pullout tests for comparison. Following the tests, the self-expandable screw with a porous surface exhibited the highest pullout force (1141.83 N), compared to 1056.86 N for the smooth self-expandable screw and 1104.25 N for the standard screw. The dissipated plastic strain energy differed among the screws, with values of 0.073 J for the porous self-expandable screw, 0.065 J for the smooth self-expandable screw, and 0.089 J for the standard pedicle screw. Notably, the porous self-expandable screw showed reduced stress on the bone-screw interface. Improving the mechanical design of pedicle screws could significantly enhance screw-bone fixation strength. The utilization of self-expandable pedicle screws with porous surface SMA sheets demonstrates superior performance, potentially mitigating complications like loosening.
Collapse
Affiliation(s)
- Mahdi Mohammad Asghari
- Department of Mechanical Engineering, K. N. Toosi University of Technology, Tehran, Iran
| | - Aisa Rassoli
- Department of Mechanical Engineering, K. N. Toosi University of Technology, Tehran, Iran
| | | |
Collapse
|
|
2
|
Xie S, Cui L, Liu J, Qing P, Li J. Impact of screw tip design on screw anchorage: mechanical testing and numerical simulation. J Orthop Surg Res 2024; 19:447. [PMID: 39080768 PMCID: PMC11287948 DOI: 10.1186/s13018-024-04841-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/06/2024] [Accepted: 06/07/2024] [Indexed: 08/03/2024] Open
Abstract
BACKGROUND Screw loosening is a commonly reported issue following spinal screw fixation and can lead to various complications. The initial cause of screw loosening is biomechanical deterioration. Previous studies have demonstrated that modifications in screw design can impact the local biomechanical environment, specifically the stress distribution on bone-screw interfaces. There are several different designs of screw tips available for clinically used pedicle screws; however, it remains unclear whether these variations affect the local stress distribution and subsequent screw anchorage ability. METHODS This study conducted comprehensive biomechanical research using polyurethane foam mechanical tests and corresponding numerical simulations to investigate this topic. Models of pedicle screw-fixed osteoporotic polyurethane foam were created with two different clinically used screw tip designs (flat and steep) featuring varying tip lengths, taper angles, and diameters, as well as identical flank overlap areas and thread designs. The anchorage ability of the different models was assessed through toggle and pull-out test. Additionally, numerical mechanical models were utilized to compute the stress distributions at the screw and bone-screw interfaces in the different models. RESULTS Mechanical tests revealed superior anchorage ability in models utilizing flat-tipped screws. Furthermore, numerical modeling indicated improved anchorage ability and reduced stress concentration tendency in these models. CONCLUSION Changes in screw tip design can significantly impact the biomechanical anchoring capability of screws. Specifically, flatter tip pedicle screws may mitigate the risk of screw loosening by alleviating stress concentration on bone-screw interfaces.
Collapse
Affiliation(s)
- Shiming Xie
- Department of Spine surgery, Mianyang Orthopedic Hospital, Mianyang, Sichuan Province, 621052, P.R. China
| | - Liqiang Cui
- Department of Spine surgery, Mianyang Orthopedic Hospital, Mianyang, Sichuan Province, 621052, P.R. China
| | - Jinhui Liu
- Sichuan Provincial Laboratory of Orthopaedic Engineering, Department of Bone and Joint Surgery, Affiliated Hospital of Southwest Medical University, Luzhou, Sichuan Province, PR China
| | - Peidong Qing
- Department of Spine surgery, Mianyang Orthopedic Hospital, Mianyang, Sichuan Province, 621052, P.R. China.
| | - Jingchi Li
- Department of Orthopedics, Luzhou Key Laboratory of Orthopedic Disorders, The Affiliated Traditional Chinese Medicine Hospital, Southwest Medical University, Luzhou, Sichuan Province, 646000, P.R. China.
| |
Collapse
|
|
3
|
Bennie S, Crowley JD, Wang T, Pelletier MH, Walsh WR. Pedicle screw pull-out testing in polyurethane foam blocks: Effect of block orientation and density. Proc Inst Mech Eng H 2024; 238:455-460. [PMID: 38480483 DOI: 10.1177/09544119241236873] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/12/2024]
Abstract
Synthetic bone models such as polyurethane (PU) foam are a well-established substitute to cadaveric bone for screw pull-out testing; however, little attention has been given to the effect of PU foam anisotropy on orthopaedic implant testing. Compressive and screw pull-out performance in three PU foam densities; 0.16 g/cm3 (PCF 10), 0.32 g/cm3 (PCF 20) and 0.64 g/cm3 (PCF 40) were performed in each of the X, Y or Z orientations. The maximum compressive force, stiffness in the linear region, maximum stress and modulus were determined for all compression tests. Pedicle screws were inserted and pulled out axially to determine maximum pull-out force, energy to failure and stiffness. One-way ANOVA and post hoc tests were used to compare outcome variables between PU foam densities and orientations, respectively. Compression tests demonstrated the maximum force was significantly different between all orientations for PCF 20 (X, Y and Z) while stiffness and maximum stress were different between X versus Y and X versus Z. Maximum pull-out force was significantly different between all orientations for PCF 10 foam. No significant differences were noted for other foam densities. There is potential for screw pull-out testing results to be significantly affected by orientation in lower density PU foams. It is recommended that a single, known orientation of the PU foam block be used for experimental testing.
Collapse
Affiliation(s)
- Stephen Bennie
- Surgical & Orthopaedic Research Laboratories (SORL), Prince of Wales Clinical School, UNSW Sydney, Sydney, NSW, Australia
| | - James Douglas Crowley
- Surgical & Orthopaedic Research Laboratories (SORL), Prince of Wales Clinical School, UNSW Sydney, Sydney, NSW, Australia
| | - Tian Wang
- Surgical & Orthopaedic Research Laboratories (SORL), Prince of Wales Clinical School, UNSW Sydney, Sydney, NSW, Australia
| | - Matthew Henry Pelletier
- Surgical & Orthopaedic Research Laboratories (SORL), Prince of Wales Clinical School, UNSW Sydney, Sydney, NSW, Australia
| | - William Robert Walsh
- Surgical & Orthopaedic Research Laboratories (SORL), Prince of Wales Clinical School, UNSW Sydney, Sydney, NSW, Australia
| |
Collapse
|
|
4
|
Li Q, Zhao H, Yang J, Song S, Liu X. Optimization of Pedicle Screw Parameters for Enhancing Implant Stability Based on Finite Element Analysis. World Neurosurg 2024; 183:e345-e354. [PMID: 38151174 DOI: 10.1016/j.wneu.2023.12.099] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2023] [Accepted: 12/18/2023] [Indexed: 12/29/2023]
Abstract
OBJECTIVE To improve implant stability parameters, including pedicle screw (PS) outer diameter, thread depth, and pitch, by finite element analysis. METHODS Insertion and pullout of the PS were simulated by finite element analysis, and the precision of simulation was evaluated by comparison with mechanical tests. Influences of the parameters on the maximum insertion torque and maximum pullout force were analyzed by computational simulations, including single-factor analysis and orthogonal experiments. RESULTS The simulation results agreed with the mechanical test results. The order of parameters influencing insertion torque and pullout force was outer diameter > pitch > thread depth. When the pilot hole diameter is 0.1 mm larger than the inner diameter of the PS, the calculated Pearson correlation coefficient between the maximum insertion torque and maximum pullout force was r = 0.99. The optimized PS had a maximum insertion torque of 485.16 N·mm and a maximum pullout force of 1726.33 N, 23.9% and 9.1% higher, respectively, than the values of standard screws. CONCLUSIONS The presently used models are feasible for evaluating the implant stability of PSs. The maximum insertion torque and maximum pullout force of PSs are highly correlated and can be improved by increasing the outer diameter and decreasing pitch. Although with the parameters of the PS, pedicle size and bone mineral density are 2 additional factors to consider for better implant stability.
Collapse
Affiliation(s)
- Qiang Li
- School of Mechanical Engineering, University of Shanghai for Science and Technology, Shanghai, People's Republic of China; Shanghai Engineering Research Center of High-Performance Medical Device Materials, Shanghai, People's Republic of China.
| | - Hu Zhao
- School of Mechanical Engineering, University of Shanghai for Science and Technology, Shanghai, People's Republic of China
| | - Jinshuai Yang
- School of Mechanical Engineering, University of Shanghai for Science and Technology, Shanghai, People's Republic of China
| | - Shihong Song
- School of Mechanical Engineering, University of Shanghai for Science and Technology, Shanghai, People's Republic of China
| | - Xuyan Liu
- School of Mechanical Engineering, University of Shanghai for Science and Technology, Shanghai, People's Republic of China
| |
Collapse
|
|
5
|
Sevillano-Perez E, Prado-Novoa M, Postigo-Pozo S, Peña-Trabalon A, Guerado E. L4 fixation is not necessary in L5-Iliac spinopelvic fixation after trauma, but coadjutant transilio-transsacral fixation is. Injury 2024; 55:111378. [PMID: 38309085 DOI: 10.1016/j.injury.2024.111378] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/16/2023] [Revised: 12/28/2023] [Accepted: 01/20/2024] [Indexed: 02/05/2024]
Abstract
INTRODUCTION Spinopelvic dissociation (SPD) is a severe injury characterized by a discontinuity between the spine and the bony pelvis consisting of a bilateral longitudinal sacral fracture, most of the times through sacral neuroforamen, and a horizontal fracture, usually through the S1 or S2 body. The introduction of the concept of triangular osteosynthesis has shown to be an advance in the stability of spinopelvic fixation (SPF). However, a controversy exists as to whether the spinal fixation should reach up to L4 and, if so, it should be combined with transiliac-transsacral screws (TTS). OBJECTIVE The purpose of this study is to compare the biomechanical behavior in the laboratory of four different osteosynthesis constructs for SPD, including spinopelvic fixation of L5 versus L4 and L5; along with or without TTS in both cases. MATERIAL AND METHODS By means of a formerly described method by the authors, an unstable standardized H-type sacral fracture in twenty synthetic replicas of a male pelvis articulated to the lumbar spine, L1 to sacrum, (Model: 1300, SawbonesTM; Pacific Research Laboratories, Vashon, WA, USA), instrumented with four different techniques, were mechanically tested. We made 4 different constructs in 5 specimen samples for each construct. Groups: Group 1. Instrumentation of the L5-Iliac bones with TTS. Group 2. Instrumentation of the L4-L5-Iliac bones with TTS. Group 3. Instrumentation of L5-Iliac bones without TTS. Group 4: Instrumentation of L4-L5-Iliac bones without TTS. RESULTS AND CONCLUSIONS According to our results, it can be concluded that in SPD, better stability is obtained when proximal fixation is only up to L5, without including L4 (alternative hypothesis), the addition of transiliac-transsacral fixations is essential.
Collapse
Affiliation(s)
| | - Maria Prado-Novoa
- Clinical Biomechanics Laboratory of Andalusia (BIOCLINA), University of Malaga, Malaga, Spain
| | - Sergio Postigo-Pozo
- Clinical Biomechanics Laboratory of Andalusia (BIOCLINA), University of Malaga, Malaga, Spain
| | - Alejandro Peña-Trabalon
- Clinical Biomechanics Laboratory of Andalusia (BIOCLINA), University of Malaga, Malaga, Spain
| | - Enrique Guerado
- School of Medicine, University of Malaga, Malaga, Spain; Department of Orthopaedic Surgery and Traumatology, Hospital Universitario Costa del Sol, Marbella Malaga, Spain.
| |
Collapse
|
|
6
|
Yang JX, Luo L, Liu JH, Wang N, Xi ZP, Li JC. Incomplete insertion of pedicle screws triggers a higher biomechanical risk of screw loosening: mechanical tests and corresponding numerical simulations. Front Bioeng Biotechnol 2024; 11:1282512. [PMID: 38260754 PMCID: PMC10800439 DOI: 10.3389/fbioe.2023.1282512] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2023] [Accepted: 12/11/2023] [Indexed: 01/24/2024] Open
Abstract
Screw loosening is a widely reported issue after spinal screw fixation and triggers several complications. Biomechanical deterioration initially causes screw loosening. Studies have shown that incomplete insertion of pedicle screws increases the risk of screw breakage by deteriorating the local mechanical environment. However, whether this change has a biomechanical effect on the risk of screw loosening has not been determined. This study conducted comprehensive biomechanical research using polyurethane foam mechanical tests and corresponding numerical simulations to verify this topic. Pedicle screw-fixed polyurethane foam models with screws with four different insertion depths were constructed, and the screw anchoring ability of different models was verified by toggle tests with alternating and constant loads. Moreover, the stress distribution of screw and bone-screw interfaces in different models was computed in corresponding numerical mechanical models. Mechanical tests presented better screw anchoring ability with deeper screw insertion, but parameters presented no significant difference between groups with complete thread insertion. Correspondingly, higher stress values can be recorded in the model without complete thread insertion; the difference in stress values between models with complete thread insertion was relatively slight. Therefore, incomplete thread insertion triggers local stress concentration and the corresponding risk of screw loosening; completely inserting threads could effectively alleviate local stress concentration and result in the prevention of screw loosening.
Collapse
Affiliation(s)
- Jie-Xiang Yang
- Department of Orthopedics, The Affiliated Traditional Chinese Medicine Hospital, Southwest Medical University, Luzhou, China
- Luzhou Key Laboratory of Orthopedic Disorders, Southwest Medical University, Luzhou, Sichuan, China
| | - Lin Luo
- Department of Orthopedics, The Affiliated Traditional Chinese Medicine Hospital, Southwest Medical University, Luzhou, China
- Luzhou Key Laboratory of Orthopedic Disorders, Southwest Medical University, Luzhou, Sichuan, China
| | - Jin-Hui Liu
- Sichuan Provincial Laboratory of Orthopaedic Engineering, Department of Bone and Joint Surgery, Affiliated Hospital of Southwest Medical University, Luzhou, Sichuan, China
| | - Nan Wang
- Department of Orthopedics, Affiliated Hospital of Integrated Traditional Chinese and Western Medicine, Nanjing University of Chinese Medicine, Nanjing, Jiangsu, China
| | - Zhi-Peng Xi
- Department of Orthopedics, Affiliated Hospital of Integrated Traditional Chinese and Western Medicine, Nanjing University of Chinese Medicine, Nanjing, Jiangsu, China
| | - Jing-Chi Li
- Department of Orthopedics, The Affiliated Traditional Chinese Medicine Hospital, Southwest Medical University, Luzhou, China
- Luzhou Key Laboratory of Orthopedic Disorders, Southwest Medical University, Luzhou, Sichuan, China
| |
Collapse
|
|
7
|
Müller JU, Nowak S, Matthes M, Pillich DT, Schroeder HWS, Müller J. Biomechanical comparison of two different compression screws for the treatment of odontoid fractures in human dens axis specimen. Clin Biomech (Bristol, Avon) 2024; 111:106162. [PMID: 38159327 DOI: 10.1016/j.clinbiomech.2023.106162] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/26/2023] [Revised: 12/13/2023] [Accepted: 12/21/2023] [Indexed: 01/03/2024]
Abstract
BACKGROUND Lag screw osteosynthesis for odontoid fractures has a high rate of pseudoarthrosis, especially in elderly patients. Besides biomechanical properties of the different screw types, insufficient fragment compression or unnoticed screw stripping may be the main causing factors for this adverse event. The aim of the study was to compare two screws in clinical use with different design principles in terms of compression force and stability against screw stripping. METHODS Twelve human cadaveric C2 vertebral bodies were considered. Bone density was determined. The specimens were matched according to bone density and randomly assigned to two experimental groups. An odontoid fracture was induced, which were fixed either with a 3.5 mm standard compression screw or with a 5 mm sleeve nut screw. Both screws are certified for the treatment of odontoid fractures. The bone samples were fixed in a measuring device. The screwdriver was driven mechanically. The tests were analyzed for peak interfragmentary compression and screw-in torque with a frequency of 20 Hz. FINDINGS The maximum fragment compression was significantly higher with screw with sleeve nut at 346.13(SD ±72.35) N compared with classic compression screw at 162.68(SD ±114.13) N (p = 0.025). Screw stripping occurred significantly earlier in classic compression screw at 255.5(SD ±192.0)° rotation after reaching maximum compression than in screw with sleeve nut at 1005.2(SD ±341.1)° (p = 0.0039). INTERPRETATION Screw with sleeve nut achieves greater fragment compression and is more robust to screw stripping compared to classic compression screw. Whether the better biomechanical properties lead to a reduction of pseudoarthrosis has to be proven in clinical studies.
Collapse
Affiliation(s)
- Jan-Uwe Müller
- Department of Neurosurgery, University Medicine, Greifswald, Germany.
| | - Stephan Nowak
- Department of Neurosurgery, University Medicine, Greifswald, Germany
| | - Marc Matthes
- Department of Neurosurgery, University Medicine, Greifswald, Germany
| | | | | | - Jonas Müller
- Department of Neurosurgery, University Medicine, Greifswald, Germany
| |
Collapse
|
|
8
|
Major JW, Ernst AJ, Kallevang JK, Kaeck A, Grijalva SD, Douglas TJ, Wilson AW, Garry CB. A radiologic determination of the different screw cutting patterns in cut and uncut orthopedic cortical screws using a novel imaging technique. Skeletal Radiol 2023; 52:2461-2467. [PMID: 37237173 DOI: 10.1007/s00256-023-04368-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Revised: 05/17/2023] [Accepted: 05/17/2023] [Indexed: 05/28/2023]
Abstract
OBJECTIVE We hypothesize that cut screws will deform in a manner that increases the core and outer diameters of the screw hole compared to uncut controls, and effects will be more pronounced in titanium screws. MATERIALS AND METHODS We used biomechanical polyurethane foam blocks to simulate cortical bone. We organized four groups of stainless steel and titanium cut and uncut screws. Blocks were fitted with a jig to ensure perpendicular screw insertion. We imaged the blocks using digital mammography and measured them using PACS software. Power analysis determined a power of 0.95 and an alpha error of 0.05. RESULTS Highly statistically significant differences in core diameter were found after cutting stainless steel and titanium screws. Cutting stainless steel screws increased core diameter by 0.30 mm (95% CI, 0.16 to 0.45; p < .001). Titanium screws' core diameter increased by 0.45 mm (95% CI, 0.30 to 0.61; p < .001). No significant differences were found in the outer diameters of stainless steel and titanium screws after cutting. CONCLUSION Titanium and stainless steel screw tracts demonstrated screw core diameter and screw thread pattern deformation after cutting. Titanium screws demonstrated more significant effects.
Collapse
Affiliation(s)
- Joshua W Major
- Department of Radiology, Naval Medical Center Portsmouth, Portsmouth, VA, 23708-2197, USA.
| | - Andrew J Ernst
- Department of Orthopaedic Surgery, Naval Medical Center Portsmouth, Portsmouth, VA, 23708-2197, USA
| | - Jonathan K Kallevang
- Department of Orthopaedic Surgery, Naval Medical Center Portsmouth, Portsmouth, VA, 23708-2197, USA
| | - Alexander Kaeck
- Department of Radiation Physics, Naval Medical Center Portsmouth, Portsmouth, VA, 23708-2197, USA
| | - Stephen D Grijalva
- Department of Orthopaedic Surgery, Naval Medical Center Portsmouth, Portsmouth, VA, 23708-2197, USA
| | - Thomas J Douglas
- Department of Orthopaedic Surgery, Naval Medical Center Portsmouth, Portsmouth, VA, 23708-2197, USA
| | - Andrew W Wilson
- Department of Orthopaedic Surgery, University of Tennessee College of Medicine Chattanooga, Chattanooga, TN, USA
| | - Conor B Garry
- Department of Orthopaedic Surgery, Naval Medical Center Portsmouth, Portsmouth, VA, 23708-2197, USA
- Department of Orthopaedic Surgery, University of Tennessee College of Medicine Chattanooga, Chattanooga, TN, USA
| |
Collapse
|
|
9
|
Pye JL, Garcia TC, Kapatkin AS, Samol MA, Stover S. Biomechanical comparison of compact versus standard flute drill bits, and interlocking versus buttress thread self-tapping cortical bone screws in cadaveric equine third metacarpal condyle. Vet Surg 2023; 52:1128-1139. [PMID: 37302003 DOI: 10.1111/vsu.13965] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2022] [Revised: 03/17/2023] [Accepted: 04/16/2023] [Indexed: 06/12/2023]
Abstract
OBJECTIVES To compare (1) performance of compact versus standard flute drill bits, (2) screw insertion properties and (3) pullout variables between interlocking thread (ITS) and buttress thread (BTS) self-tapping screws in third metacarpi. STUDY DESIGN In vitro experimental study. SAMPLE POPULATION Paired third metacarpi from 11 Thoroughbreds aged 2-4 years. METHODS Screws were inserted into the lateral condylar fossae following bone preparation using the respective drill bit for each screw type. Screw pullout was achieved using a mechanical testing system. Density and porosity of bone surrounding screw holes was measured with microcomputed tomography following each pullout test. Drilling, screw insertion and pullout variables were compared between drill bit and screw types using repeated measures ANOVA. Linear regression analyses were used to characterize relationships between bone tissue properties and drill bit and screw outcomes. RESULTS Maximum torque power spectral density (PSD) was lower for compact flute drill bits. Insertion torque was 50% higher for ITS. BTS had 33% greater preyield stiffness and 7% greater mean yield force. Bone tissue properties affected measured variables similarly for both screw and drill bit types. CONCLUSIONS Lower torque PSD may increase durability of the compact flute drill bit. ITS had greater insertional torque, which may reflect greater bone engagement. BTS had greater resistance to axial pullout forces. CLINICAL SIGNIFICANCE Metacarpal bone provides a simple model for comparison of drill bit and screw designs. Use of ITS to repair equine fractures subject to predominantly tensile forces is not justified based on the results of this study.
Collapse
Affiliation(s)
- Jannah L Pye
- William R. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, California, USA
| | - Tanya C Garcia
- JD Wheat Veterinary Orthopedic Research Laboratory, School of Veterinary Medicine, University of California-Davis, Davis, California, USA
| | - Amy S Kapatkin
- JD Wheat Veterinary Orthopedic Research Laboratory, School of Veterinary Medicine, University of California-Davis, Davis, California, USA
- Department of Surgical & Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, California, USA
| | - Monika A Samol
- California Animal Health and Food Safety System, San Bernadino Branch, School of Veterinary Medicine, University of California-Davis, Davis, California, USA
| | - Susan Stover
- JD Wheat Veterinary Orthopedic Research Laboratory, School of Veterinary Medicine, University of California-Davis, Davis, California, USA
- Department of Surgical & Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, California, USA
| |
Collapse
|
|
10
|
Salunke P, Karthigeyan M, Uniyal P, Mishra K, Gupta T, Kumar N. A Novel Pedicle Screw Design with Variable Thread Geometry: Biomechanical Cadaveric Study with Finite Element Analysis. World Neurosurg 2023; 172:e144-e150. [PMID: 36587893 DOI: 10.1016/j.wneu.2022.12.120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2022] [Revised: 12/27/2022] [Accepted: 12/28/2022] [Indexed: 12/31/2022]
Abstract
BACKGROUND Pedicle screw fixation provides one of the most stable spinal constructs. Their designs together with osseous characteristics have been known to influence the screw-bone interplay during surgical maneuvers and thereafter the fusion process. Various technical modifications to enhance screw performance have been suggested. This study evaluated the pull-out strength and axial stiffness of a novel pedicle screw design with variable thread geometry and pitch. METHODS The newly designed triple threaded pedicle screw is tapered, and has unique out-turned flanges to hold the cancellous bone and a finer pitch at its distal and proximal end to engage the cortical bone. Five lumbar and 4 lower thoracic cadaveric vertebrae were divided into hemivertebrae. A standard cancellous pedicle screw and the newly designed pedicle screw were inserted into each hemivertebra. Axial stiffness and peak pull-out force between the screw types were compared; a finite element analysis was also performed to additionally compare the pull out under toggle forces. RESULTS In cadaveric study, the axial stiffness of the new screw was significantly better than that of the standard screw. However, the peak load between the screws was not statistically different. Finite element analyses suggested lesser stress at bone-implant interface for the new screw along with better axial stiffness under both co-axial and toggle forces. CONCLUSIONS Our novel pedicle screw design with variable thread geometry demonstrates greater axial stiffness compared with the standard screws, and therefore is likely to withstand a greater surgical manipulation.
Collapse
Affiliation(s)
- Pravin Salunke
- Department of Neurosurgery, Postgraduate Institute of Medical Education & Research (PGIMER), Chandigarh, India
| | - Madhivanan Karthigeyan
- Department of Neurosurgery, Postgraduate Institute of Medical Education & Research (PGIMER), Chandigarh, India.
| | - Piyush Uniyal
- Department of Mechanical Engineering, Indian Institute of Technology (IIT), Ropar, Punjab, India
| | - Keshav Mishra
- Department of Neurosurgery, Postgraduate Institute of Medical Education & Research (PGIMER), Chandigarh, India
| | - Tulika Gupta
- Department of Anatomy, PGIMER, Chandigarh, India
| | - Navin Kumar
- Department of Mechanical Engineering, Indian Institute of Technology (IIT), Ropar, Punjab, India
| |
Collapse
|
|
11
|
Liu YY, Xiao J, He L, Yin X, Song L, Zhou R, Zeng J, Liu P, Dai F. Risk factor analysis of bone cement leakage for polymethylmethacrylate-augmented cannulated pedicle screw fixation in spinal disorders. Heliyon 2023; 9:e15167. [PMID: 37089395 PMCID: PMC10113860 DOI: 10.1016/j.heliyon.2023.e15167] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2022] [Revised: 03/25/2023] [Accepted: 03/28/2023] [Indexed: 04/05/2023] Open
Abstract
Objective To investigate the risk factors of cement leakage (CL) for polymethylmethacrylate-augmented cannulated pedicle screw (CPS) in spinal degenerative diseases and provided technical guidance for clinical surgery. Methods This study enrolled 276 patients with spinal degenerative disease and osteoporosis who were augmented using CPSs (835 screws in total) from May 2011 to June 2018 in our hospital. The patients' age, sex, bone mineral density (BMD), diagnosis, augmented positions, number of CPS implanted, and CL during surgery were recorded. CL was observed by postoperative computed tomography (CT) and was classified by Yeom typing. Results A total of 74 (74/835, 8.9%) CPSs in 64 patients leaked (64/276, 23.2%). CL was significantly correlated with the number and position of screws (P < 0.05), but not with sex, age, and BMD (P > 0.05). The position, number of CPSs, fracture, degenerative scoliosis, ankylosing spondylitis, and revision surgery were risk factors for CL (P < 0.05). Augmentation of the thoracic vertebral body, fracture, and ankylosing spondylitis were independent risk factors for Type S. Augmentation of the lumbar vertebral body, lumbar disc herniation, and lumbar spondylolisthesis were independent risk factors for Type B (P < 0.05). Conclusions CL has a high incidence in clinical practice. High-risk factors for leakage should be addressed to avoid serious complications. Particularly, it is necessary to develop alternative solutions once CPSs can't be used in surgery caused by CL.
Collapse
Affiliation(s)
- Yao-yao Liu
- Department of Spine Surgery, Daping Hospital, Army Medical Center of PLA, Chongqing, 400042, PR China
| | - Jun Xiao
- Guangzhou Rocket Force Special Service Convalescent Center, Guangzhou, 510515, PR China
| | - Lei He
- Department of Orthopedics, Southwest Hospital of Army Medical University, PLA, Chongqing, 400038, PR China
| | - Xiang Yin
- Department of Spine Surgery, Daping Hospital, Army Medical Center of PLA, Chongqing, 400042, PR China
| | - Lei Song
- Department of Orthopedics, Southwest Hospital of Army Medical University, PLA, Chongqing, 400038, PR China
| | - Rui Zhou
- Department of Orthopedics, Southwest Hospital of Army Medical University, PLA, Chongqing, 400038, PR China
| | - Jing Zeng
- Guangzhou Rocket Force Special Service Convalescent Center, Guangzhou, 510515, PR China
| | - Peng Liu
- Department of Spine Surgery, Daping Hospital, Army Medical Center of PLA, Chongqing, 400042, PR China
- Corresponding author. Department of Spine surgery, Daping Hospital, Army Medical Center of PLA, No. 10 Changjiang Road, Yuzhong District, Chongqing, 400042, PR China.
| | - Fei Dai
- Department of Orthopedics, Southwest Hospital of Army Medical University, PLA, Chongqing, 400038, PR China
- Corresponding author. Department of Orthopedics, Southwest Hospital of Army Medical University, PLA, No. 30 Gaotanyan Street, Shapingba District, Chongqing, 400038, PR China.
| |
Collapse
|
|
12
|
Song L, Xiao J, Zhou R, Li CC, Zheng TT, Dai F. Clinical evaluation of the efficacy of a new bone cement-injectable cannulated pedicle screw in the treatment of spondylolysis-type lumbar spondylolisthesis with osteoporosis: a retrospective study. BMC Musculoskelet Disord 2022; 23:951. [PMID: 36329431 PMCID: PMC9632048 DOI: 10.1186/s12891-022-05904-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Accepted: 10/21/2022] [Indexed: 11/06/2022] Open
Abstract
Purpose To investigate the clinical efficacy and safety of a bone cement-injectable cannulated pedicle screw (CICPS) in the treatment of spondylolysis-type lumbar spondylolisthesis with osteoporosis. Methods A retrospective study was conducted on 37 patients (Dual-energy X-ray bone density detection showed different degrees of osteoporosis) with spondylolysis-type lumbar spondylolisthesis who underwent lumbar spondylolisthesis reduction and fusion using a new type of injectable bone cement screw from May 2011 to March 2015. Postoperative clinical efficacy was evaluated by the Visual Analogue Scale (VAS) scores and the Oswestry Disability Index (ODI). Imaging indexes were used to evaluate the stability of internal fixation of the devices 1, 3, 6, and 12 months after surgery and annually thereafter. The safety of the CICPS was assessed by the prevalence of intraoperative and postoperative complications. Results A total of 124 CICPS were implanted intraoperatively. Bone cement leakage occurred in 3 screws (2.42%), and no clinical discomfort was found in any patients. All 37 patients were followed up with an average follow-up time of 26.6 ± 13.4 months (12–58 months). In the evaluation of the clinical effects of the operation, the average postoperative VAS score of the patients decreased from 4.30 ± 1.58 before surgery to 0.30 ± 0.70 after surgery (P < 0.001), and the ODI decreased from 47.27% ± 16.97% before surgery to 3.36% ± 5.70% after surgery (P < 0.001). No screw was loose, broken or pulled out. Conclusion CICPS is safe and effective in the treatment of spondylolysis-type lumbar spondylolisthesis complicated by osteoporosis.
Collapse
Affiliation(s)
- Lei Song
- Department of Orthopaedics, First Affiliated Hospital, Army Medical University, Chongqing, 400038, People's Republic of China
| | - Jun Xiao
- Department of Special Service Physiological Training, Guangzhou Special Service Recuperation Center of PLA Rocket Force, Guangzhou, 515515, People's Republic of China
| | - Rui Zhou
- Department of Orthopaedics, First Affiliated Hospital, Army Medical University, Chongqing, 400038, People's Republic of China
| | - Cong-Can Li
- Department of Orthopaedics, First Affiliated Hospital, Army Medical University, Chongqing, 400038, People's Republic of China
| | - Ting-Ting Zheng
- Department of Orthopaedics, First Affiliated Hospital, Army Medical University, Chongqing, 400038, People's Republic of China.
| | - Fei Dai
- Department of Orthopaedics, First Affiliated Hospital, Army Medical University, Chongqing, 400038, People's Republic of China.
| |
Collapse
|
|
13
|
Novel Dual-Threaded Pedicle Screws Provide Fixation Stability That Is Comparable to That of Traditional Screws with Relative Bone Preservation: An In Vitro Biomechanical Study. APPLIED SCIENCES-BASEL 2022. [DOI: 10.3390/app12126172] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Replacement with larger diameter screws is always used in pedicle screw loosening but carries a risk of pedicle wall violation. A pedicle screw with more preserved bone stock is the preferred primary fixation choice. The purpose of this study was to evaluate whether a newly designed proximal-conical dual-thread screw with less bone occupancy provides fixation strength comparable to that of a traditional screw. Six types of pedicle screws based on three different shapes (cylindrical, conical, and proximal-conical) and two thread profiles (single-thread and dual-thread) were grouped. Conical and proximal-conical screws differed mainly in the slope of the outer diameter from the hub to the tip. Conical screws had an outer diameter (6.5 mm) that differed from the hub and tapered by 30% to an outer diameter (4.5 mm) at the tip and proximal-conical screws had the same outer diameter from the hub and tapered by 30% (4.5 mm) at 20 mm from the hub and then maintained the outer diameter (45 mm) to the tip. A total of 36 L4 Sawbones® vertebrae were used in the study and six trials for each screw group. The results of the imaging, screw volume in bone, insertion torque, and pullout force were analyzed. For screws with the same shape, insertion torque and pullout force were significantly higher for those in the dual-thread groups than for those in the single-thread groups (p < 0.05). For screws with the same thread profile, there was no significant difference in either biomechanical test between the different screw shapes (p > 0.05). Our results demonstrated that these proximal-conical dual-thread screws, with the property of relative bone stock preservation, display a comparable biomechanical performance to traditional dual-thread screws and a better performance than single-thread screws. This screw design could serve as the primary pedicle screw choice to reduce revision difficulty.
Collapse
|
|
14
|
Yao GL, Xiao ZZ, Xiao T, Zhong NS, Huang SH, Liu JM, Liu ZL. Development and biomechanical test of a new pedicle screw for thoracolumbar spinal surgery. Med Eng Phys 2022; 104:103808. [DOI: 10.1016/j.medengphy.2022.103808] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2021] [Revised: 04/21/2022] [Accepted: 04/21/2022] [Indexed: 11/26/2022]
|
|
15
|
Weidling M, Heilemann M, Schoenfelder S, Heyde CE. Influence of thread design on anchorage of pedicle screws in cancellous bone: an experimental and analytical analysis. Sci Rep 2022; 12:8051. [PMID: 35577852 PMCID: PMC9110386 DOI: 10.1038/s41598-022-11824-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Accepted: 04/28/2022] [Indexed: 11/12/2022] Open
Abstract
Threads of modern pedicle screws can vary greatly in design. It is difficult to assess which interplay of design features is particularly advantageous for screw anchorage. This study aims to increase the understanding of the anchorage behaviour between screw and cancellous bone. Pull-out tests of six pedicle screws in two sizes each were performed on three densities of biomechanical test material. More general screw characteristics were derived from the screw design and evaluated using the test data. Selected screws were tested on body donor material. Some screw characteristics, such as compacting, are well suited to compare the different thread designs of screws with tapered core. The combination of two characteristics, one representing bone compacting and one representing thread flank area, appears to be particularly advantageous for assessing anchorage behaviour. With an equation derived from these characteristics, the pull-out strength could be calculated very accurately (mean deviation 1%). Furthermore, findings are corroborated by tests on donor material. For screws with tapered core, the design demands for good anchorage against pull-out from cancellous bone change with material density. With sufficient bone quality, screws with a high compacting effect are advantageous, while with low bone density a high thread flank area also appears necessary for better screw anchorage.
Collapse
Affiliation(s)
- Martin Weidling
- Department of Orthopaedic Surgery, Traumatology and Plastic Surgery, ZESBO - Center for Research on Musculoskeletal Systems, Leipzig University, Leipzig, Germany.
| | - Martin Heilemann
- Department of Orthopaedic Surgery, Traumatology and Plastic Surgery, ZESBO - Center for Research on Musculoskeletal Systems, Leipzig University, Leipzig, Germany
| | - Stephan Schoenfelder
- Faculty of Engineering, University of Applied Sciences Leipzig, Leipzig, Germany
| | - Christoph E Heyde
- Department of Orthopaedic Surgery, Traumatology and Plastic Surgery, Leipzig University Medical Center, Leipzig, Germany
| |
Collapse
|
|
16
|
Biomechanical Comparison of Fixation Stability among Various Pedicle Screw Geometries: Effects of Screw Outer/Inner Projection Shape and Thread Profile. APPLIED SCIENCES-BASEL 2021. [DOI: 10.3390/app11219901] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The proper screw geometry and pilot-hole size remain controversial in current biomechanical studies. Variable results arise from differences in specimen anatomy and density, uncontrolled screw properties and mixed screw brands, in addition to the use of different tapping methods. The purpose of this study was to evaluate the effect of bone density and pilot-hole size on the biomechanical performance of various pedicle screw geometries. Six screw designs, involving three different outer/inner projections of screws (cylindrical/conical, conical/conical and cylindrical/cylindrical), together with two different thread profiles (square and V), were examined. The insertional torque and pullout strength of each screw were measured following insertion of the screw into test blocks, with densities of 20 and 30 pcf, predrilled with 2.7-mm/3.2-mm/3.7-mm pilot holes. The correlation between the bone volume embedded in the screw threads and the pullout strength was statistically analyzed. Our study demonstrates that V-shaped screw threads showed a higher pullout strength than S-shaped threads in materials of different densities and among different pilot-hole sizes. The configuration, consisting of an outer cylindrical shape, an inner conical shape and V-shaped screw threads, showed the highest insertional torque and pullout strength at a normal and higher-than-normal bone density. Even with increasing pilot-hole size, this configuration maintained superiority.
Collapse
|
|
17
|
Banas M, Hore N, Buchfelder M, Brandner S. Assessment of conformity of actual thoraco-lumbar pedicle screw dimensions to manufacturers' specifications. Sci Prog 2021; 104:368504211035035. [PMID: 34398723 PMCID: PMC10358464 DOI: 10.1177/00368504211035035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Although correct selection of pedicle screw dimensions is indispensable to achieving optimum results, manufacturer-specified or intended dimensions may differ from actual dimensions. Here we analyzed the reliability of specifications made by various manufacturers by comparing them to the actual lengths and diameters of pedicle screws in a standardized experimental setup. We analyzed the actual length and diameter of pedicle screws of five different manufacturers. Four different screw lengths and for each length two different diameters were measured. Measurements were performed with the pedicle screws attached to a rod, with the length determined from the bottom of the tulip to the tip of the screw and the diameters determined at the proximal and distal threads. Differences in length of > 1 mm were found between the manufacturers' specifications and our actual measurements in 24 different pedicle screws. The highest deviation of the measured length from the manufacturers' specification was 3.2 mm. The difference in length between the shortest and longest screw with identical specifications was 3.4 mm. The highest deviation of the measured proximal thread diameters and the manufacturer's specifications was 0.5 mm. The diameter of the distal thread depends on the shape of the pedicle screw and hence varies between manufacturers in conical screws. We found clear differences in the length of pedicle screws with identical manufacturer specifications. Since differences between the actual dimensions and the dimensions indicated by the manufacturer may vary, this needs to be taken into account during the planning of spine instrumentation.
Collapse
Affiliation(s)
- Marian Banas
- Department of Neurosurgery, University Hospital Erlangen, Erlangen, Germany
- Department of Neurosurgery, Clinic Hohe Warte, Bayreuth, Germany
| | - Nirjhar Hore
- Department of Neurosurgery, University Hospital Erlangen, Erlangen, Germany
| | - Michael Buchfelder
- Department of Neurosurgery, University Hospital Erlangen, Erlangen, Germany
| | - Sebastian Brandner
- Department of Neurosurgery, University Hospital Erlangen, Erlangen, Germany
| |
Collapse
|
|
18
|
Bokov A, Pavlova S, Bulkin A, Aleynik A, Mlyavykh S. Potential contribution of pedicle screw design to loosening rate in patients with degenerative diseases of the lumbar spine: An observational study. World J Orthop 2021; 12:310-319. [PMID: 34055588 PMCID: PMC8152435 DOI: 10.5312/wjo.v12.i5.310] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/10/2021] [Revised: 02/15/2021] [Accepted: 03/28/2021] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND The majority of published data report the results of biomechanical tests of various design pedicle screw performance. The clinical relevance and relative contribution of screw design to instrumentation stability have been insufficiently studied. AIM To estimate the contribution of screw design to rate of pedicle screw loosening in patients with degenerative diseases of the lumbar spine. METHODS This study is a prospective evaluation of 175 patients with degenerative diseases and instability of the lumbar spine segments. Participants underwent spinal instrumentation employing pedicle screws with posterior only or transforaminal interbody fusion. Follow-up was for 18 mo. Patients with signs of pedicle screw loosening on computed tomography were registered; logistic regression analysis was used to identify the factors that influenced the rate of loosening. RESULTS Parameters included in the analysis were screw geometry, type of thread, external and internal screw diameter and helical pitch, bone density in Hounsfield units, number of levels fused, instrumentation without anterior support, laminectomy, and unilateral and bilateral total facet joint resection. The rate of screw loosening decreased with the increment in outer diameter, decrease in core diameter and helical pitch. The rate of screw loosening correlated positively with the number of fused levels and decreasing bone density. Bilateral facet joint removal significantly favored pedicle screw loosening. The influence of other factors was insignificant. CONCLUSION Screw parameters had a significant impact on the loosening rate along with bone quality characteristics, the number of levels fused and the extensiveness of decompression. The significance of the influence of screw parameters was comparable to those of patient- and surgery-related factors. Pedicle screw loosening was influenced by helical pitch, inner and outer diameter, but screw geometry and thread type were insignificant factors.
Collapse
Affiliation(s)
- Andrey Bokov
- Department of Oncology and Neurosurgery, Federal State Budgetary Educational Institution of Higher Education “Privolzhsky Research Medical University” of the Ministry of Health of the Russian Federation, Nizhniy Novgorod 603000, Russia
| | - Svetlana Pavlova
- Department of Oncology and Neurosurgery, Federal State Budgetary Educational Institution of Higher Education “Privolzhsky Research Medical University” of the Ministry of Health of the Russian Federation, Nizhniy Novgorod 603000, Russia
| | - Anatoliy Bulkin
- Department of Oncology and Neurosurgery, Federal State Budgetary Educational Institution of Higher Education “Privolzhsky Research Medical University” of the Ministry of Health of the Russian Federation, Nizhniy Novgorod 603000, Russia
| | - Alexandr Aleynik
- Department of Oncology and Neurosurgery, Federal State Budgetary Educational Institution of Higher Education “Privolzhsky Research Medical University” of the Ministry of Health of the Russian Federation, Nizhniy Novgorod 603000, Russia
| | - Sergey Mlyavykh
- Department of Oncology and Neurosurgery, Federal State Budgetary Educational Institution of Higher Education “Privolzhsky Research Medical University” of the Ministry of Health of the Russian Federation, Nizhniy Novgorod 603000, Russia
| |
Collapse
|
|
19
|
Çetin A, Bircan DA. Experimental investigation of pull-out performance of pedicle screws at different polyurethane (PU) foam densities. Proc Inst Mech Eng H 2021; 235:709-716. [PMID: 33730935 DOI: 10.1177/09544119211002587] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Pedicle bone screws are one of the most critical materials used in spinal orthopaedic operations. Screw loosening and pull-out (PO) are basic complications encountered during or after surgery. Pull-out Strength (POS) of the bone is one of the significant parameters to understand the mechanical behaviour of a screw fixed to poor quality or osteoporotic bone. This study investigates how the POS of a pedicle screw is affected by the factors of the screw diameter and the polyurethane (PU) foam density by experimental analysis. In the experiments, two different diameter (5.5 and 6.5 mm) of conical pedicle screws and five different density (0.08, 0.16, 0.24, 0.32 and 0.48 g·cm-3) PU foams were used. According to the force-displacement curves obtained from experimental results, the POS increased with the increases in screw diameter and PU foam density.
Collapse
Affiliation(s)
- Ahmet Çetin
- Department of Mechanical Engineering, Çukurova University, Adana, Turkey
| | - Durmuş Ali Bircan
- Department of Mechanical Engineering, Çukurova University, Adana, Turkey
| |
Collapse
|
|
20
|
Partial Threading of Pedicle Screws in a Standard Construct Increases Fatigue Life: A Biomechanical Analysis. APPLIED SCIENCES-BASEL 2021. [DOI: 10.3390/app11041503] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
This study proposed a pedicle screw design where the proximal 1/3 of the screw is unthreaded to improve fixation in posterior spinal surgery. This design was also expected to reduce the incidence of mechanical failure often observed when an unsupported screw length is exposed outside the vertebra in deformed or degenerated segments. The aim of this study was to evaluate the fatigue life of the novel pedicle screw design using finite element analysis and mechanical testing in a synthetic spinal construct in accordance with American Society for Testing and Materials (ASTM) F1717. The following setups were evaluated: (i) pedicle screw fully inserted into the test block (EXP-FT-01 and EXP-PU-01; full thread (FT), proximal unthread (PU)) and (ii) pedicle screw inserted but leaving an exposed shaft length of 7.6 mm (EXP-FT-02 and EXP-PU-02). Corresponding finite element models FEM-FT-01, FEM-FT-02, FEM-PU-01, and FEM-PU-02 were also constructed and subjected to the same loading conditions as the experimental groups. The results showed that under a 220 N axial load, the EXP-PU-01 group survived the full 5 million cycles, the EXP-PU-02 group failed at 4.4 million cycles on average, and both EXP-FT-01 and EXP-FT-02 groups failed after less than 1.0 million cycles on average, while the fatigue strength of the EXP-FT-02 group was the lowest at 170 N. The EXP-FT-01 and EXP-FT-02 constructs failed through fracture of the pedicle screw, but a rod fractured in the EXP-PU-02 group. In comparison to the FEM-FT-01 model, the maximum von Mises stress on the pedicle screw in the FEM-PU-01 and FEM-PU-02 models decreased by −43% and −27%, respectively. In conclusion, this study showed that having the proximal 1/3 of the pedicle screw unthreaded can reduce the risk of screw fatigue failure when used in deformed or degenerated segments.
Collapse
|
|
21
|
Spiegl UJ, Weidling M, Schleifenbaum S, Reinhardt M, Heyde CE. Comparison of Long Segmental Dorsal Stabilization with Complete Versus Restricted Pedicle Screw Cement Augmentation in Unstable Osteoporotic Midthoracic Vertebral Body Fractures: A Biomechanical Study. World Neurosurg 2020; 143:e541-e549. [PMID: 32777399 DOI: 10.1016/j.wneu.2020.08.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2020] [Revised: 07/30/2020] [Accepted: 08/01/2020] [Indexed: 12/13/2022]
Abstract
OBJECTIVE To compare the construct stability of long-segmental dorsal stabilization in unstable midthoracic osteoporotic fracture situation with complete pedicle screw cement augmentation (ComPSCA) versus restricted pedicle screw cement augmentation (ResPSCA) of the most cranial and caudal pedicle screws. METHODS Twelve fresh frozen human cadaveric specimens (Th 4-Th 10) aged 65 years and older were tested in a biomechanical cadaver study. All specimens received a dual-energy X-ray absorption scan and computed tomography scan before testing. Standardized long segmental stabilization was performed. All specimens were matched into pairs. These pairs were randomized into the groups with ComPSCA and ResPSCA. An unstable Th7 fracture was simulated. The maximum load was tested with 6 mm/min until failure or 20 mm had been reached. After testing, a computed tomography scan was performed. RESULTS The mean age of the specimens was 87.8 years (range 74-101 years). The mean t score was -3.6 (range -1.2 to -5.3). The mean maximum force in the ResPSCA group was 1600 N (range 1119-1880 N) and 1941 N (1183-3761 N) in the ComPSCA group. No statistically significant differences between both study groups (P = 1.0) could be seen. No signs of screw loosening were visible. CONCLUSIONS No statistically significant differences in the maximum loads could be seen. No screw loosening of the non-cemented screws was visible. Thus, the construct stability of long segmental posterior stabilization of an unstable midthoracic fracture using ResPSCA seems to be comparable with ComPSCA under axial compression.
Collapse
Affiliation(s)
- Ulrich J Spiegl
- Department of Orthopaedic, Trauma and Reconstructive Surgery, University Hospital Leipzig, Leipzig, Germany.
| | - Martin Weidling
- Center for Research on Musculoskeletal Systems (ZESBO), Faculty of Medicine, University Hospital Leipzig, Leipzig, Germany
| | - Stefan Schleifenbaum
- Center for Research on Musculoskeletal Systems (ZESBO), Faculty of Medicine, University Hospital Leipzig, Leipzig, Germany
| | - Martin Reinhardt
- Department of Diagnostic and Interventional Radiology, University Hospital Leipzig, Leipzig, Germany
| | - Christoph-E Heyde
- Department of Orthopaedic, Trauma and Reconstructive Surgery, University Hospital Leipzig, Leipzig, Germany; Center for Research on Musculoskeletal Systems (ZESBO), Faculty of Medicine, University Hospital Leipzig, Leipzig, Germany
| |
Collapse
|
|
22
|
Müller JU, Müller J, Marx S, Matthes M, Nowak S, Schroeder HWS, Pillich DT. Biomechanical comparison of three different compression screws for treatment of odontoid fractures evaluation of a new screw design. Clin Biomech (Bristol, Avon) 2020; 77:105049. [PMID: 32497928 DOI: 10.1016/j.clinbiomech.2020.105049] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/30/2020] [Revised: 05/12/2020] [Accepted: 05/15/2020] [Indexed: 02/07/2023]
Abstract
BACKGROUND Lag screw osteosynthesis in odontoid fractures shows a high rate of pseudarthrosis. Biomechanical properties may play a role with insufficient fragment compression or unnoticed screw stripping. A biomechanical comparison of different constructed lag-screws was carried out and the biomechanical properties determined. METHODS Two identical compression screws with different pilot holes (1.25 and 2.5 mm), a double-threaded screw and one sleeve-nut-screw were tested on artificial bone (Sawbone, densities 10-30pcf). Fragment compression and torque were continuously measured using thin-film force sensors (Flexiforce A201, Tekscan) and torque sensors (PCE-TM 80, PCE GmbH). FINDINGS The lowest compression reached the double-threaded screw. Compression and sleeve-nut-screw achieved 214-298% and 325-546%, respectively, of the compression force of double-threaded-screw, depending on the test material. The pilot hole optimization led to a significant improvement in compression only in the densest test material. Screw stripping took place significantly later with increasing density of the test material on all screws. In compression screws this was done at a screw rotation of 180-270°, in sleeve nut screw at 270-720° and in double-threaded screws at 300-600° after reaching the maximum compression. INTERPRETATION Double-threaded screw is robust against screw stripping, but achieves only low fragment compression. The classic compression screws achieve better compression, but are sensitive to screw stripping. Sleeve-nut screw is superior in compression and as robust as double-threaded screw against screw stripping. Whether the better biomechanical properties lead to a reduction in pseudarthrosis must be proven in clinical trials.
Collapse
Affiliation(s)
- Jan-Uwe Müller
- Department of Neurosurgery, University Medicine Greifswald, Greifswald, Germany.
| | - Jonas Müller
- Department of Neurosurgery, University Medicine Greifswald, Greifswald, Germany
| | - Sascha Marx
- Department of Neurosurgery, University Medicine Greifswald, Greifswald, Germany
| | - Marc Matthes
- Department of Neurosurgery, University Medicine Greifswald, Greifswald, Germany
| | - Stephan Nowak
- Department of Neurosurgery, University Medicine Greifswald, Greifswald, Germany
| | | | - Dirk Thomas Pillich
- Department of Neurosurgery, University Medicine Greifswald, Greifswald, Germany
| |
Collapse
|
|
23
|
Use of longer sized screws is a salvage method for broken pedicles in osteoporotic vertebrae. Sci Rep 2020; 10:10441. [PMID: 32591573 PMCID: PMC7320151 DOI: 10.1038/s41598-020-67489-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2020] [Accepted: 06/05/2020] [Indexed: 11/09/2022] Open
Abstract
Screw loosening due to broken pedicles is a common complication resulting from the insertion of screws either with inadequate diameters or into an osteoporotic pedicle. In this novel in vitro study, we tried to clarify the contribution of the pedicle to screw fixation and subsequent salvage strategies using longer or larger-diameter screws in broken pedicles. Sixty L4 fresh-frozen lumbar vertebrae harvested from mature pigs were designed as the normal-density group (n = 30) and decalcified as the osteoporosis group (n = 30). Three modalities were randomly assigned as intact pedicle (n = 30), semi-pedicle (n = 15), and non-pedicle (n = 15) in each group. Three sizes of polyaxial screws (diameter × length of 6.0 mm × 45 mm, 6.0 mm × 50 mm, and 6.5 mm × 45 mm) over five trials were used in each modality. The associations between bone density, pedicle modality and screw pullout strength were analyzed. After decalcification for 4 weeks, the area bone mineral density decreased to approximately 56% (p < 0.05) of the normal-density group, which was assigned as the osteoporosis group. An appropriate screw trajectory and insertional depth were confirmed using X-ray imaging prior to pullout testing in both groups. The pullout forces of larger-diameter screws (6.5 mm × 45 mm) and longer screws (6.0 mm × 50 mm) were significantly higher (p < 0.05) in the semi- and non-pedicle modalities in the normal-density group, whereas only longer screws (6.0 mm × 50 mm) had a significantly higher (p < 0.05) pullout force in the non-pedicle modalities in the osteoporosis group. The pedicle plays an important role in both the normal bone density group and the osteoporosis group, as revealed by analyzing the pullout force percentage contributed by the pedicle. Use of a longer screw would be a way to salvage a broken pedicle of osteoporotic vertebra.
Collapse
|
|
24
|
A novel parameter for the prediction of pedicle screw fixation in cancellous bone - A biomechanical study on synthetic foam. Med Eng Phys 2020; 79:44-51. [DOI: 10.1016/j.medengphy.2020.03.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Revised: 01/17/2020] [Accepted: 03/01/2020] [Indexed: 11/21/2022]
|
|
25
|
DeBaun MR, Swinford ST, Chen MJ, Thio T, Behn AA, Lucas JF, Bishop JA, Gardner MJ. Biomechanical comparison of bone-screw-fasteners versus traditional locked screws in plating female geriatric bone. Injury 2020; 51:193-198. [PMID: 31703961 DOI: 10.1016/j.injury.2019.10.032] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/23/2019] [Revised: 10/07/2019] [Accepted: 10/14/2019] [Indexed: 02/02/2023]
Abstract
OBJECTIVES To biomechanically compare plated constructs using nonlocking bone-screw-fasteners with interlocking threads versus locking screws with traditional buttress threads in geriatric female bone. METHODS Eleven matched pairs of proximal and distal segments of geriatric female cadaveric tibias were used to create a diaphyseal fracture model. Nonlocking bone-screw-fasteners or locking buttress threaded screws were applied to a locking compression plate on the anterolateral aspect of the tibia placed in bridge mode. Specimens were subjected to incrementally increasing cyclic axial load combined with constant cyclic torsion. Total cycles to failure served as a primary outcome measure, with failure defined as 2 mm of displacement or 10 degrees of rotation. Secondary outcome measures included initial stiffness in compression and torsion determined from preconditioning testing and overall rigidity as determined by maximum peak-to-peak axial and rotational motion at 500 cycle intervals during cyclic testing. Group comparisons were made using paired Student's t-tests. Significance was set at p < 0.05. RESULTS Bone-screw-fastener constructs failed at an average of 40,636 ± 22,151 cycles and locking screw constructs failed at an average of 37,773 ± 8433 cycles, without difference between groups (p = =0.610). Total cycles to failure was higher in the bone-screw-fasteners group for 7 tibiae out of the eleven matched pairs tested. During static and cyclic testing, bone-screw-fastener constructs demonstrated increased initial torsional stiffness (7.6%) and less peak-to-peak displacement and rotation throughout the testing cycle(p < 0.05). CONCLUSIONS In female geriatric bone, constructs fixed with bone-screw-fasteners incorporate multiplanar interlocking thread geometry and performed similarly to traditional locked plating. These novel devices may combine the benefits of both nonlocking and locking screws when plating geriatric bone.
Collapse
Affiliation(s)
- Malcolm R DeBaun
- Department of Orthopaedics, School of Medicine, Stanford University, 450 Broadway St., MC 6342, Redwood City, CA 94063, United States
| | - Steven T Swinford
- Department of Orthopaedics, School of Medicine, Stanford University, 450 Broadway St., MC 6342, Redwood City, CA 94063, United States
| | - Michael J Chen
- Department of Orthopaedics, School of Medicine, Stanford University, 450 Broadway St., MC 6342, Redwood City, CA 94063, United States
| | - Timothy Thio
- Department of Orthopaedics, School of Medicine, Stanford University, 450 Broadway St., MC 6342, Redwood City, CA 94063, United States
| | - Anthony A Behn
- Department of Orthopaedics, School of Medicine, Stanford University, 450 Broadway St., MC 6342, Redwood City, CA 94063, United States
| | | | - Julius A Bishop
- Department of Orthopaedics, School of Medicine, Stanford University, 450 Broadway St., MC 6342, Redwood City, CA 94063, United States
| | - Michael J Gardner
- Department of Orthopaedics, School of Medicine, Stanford University, 450 Broadway St., MC 6342, Redwood City, CA 94063, United States.
| |
Collapse
|
|
26
|
Takenaka S, Kaito T, Ishii K, Watanabe K, Watanabe K, Shinohara A, Harada T, Nakada F, Majima Y, Matsumoto M. Influence of novel design alteration of pedicle screw on pull-out strength: A finite element study. J Orthop Sci 2020; 25:66-72. [PMID: 30902538 DOI: 10.1016/j.jos.2019.03.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Revised: 02/19/2019] [Accepted: 03/01/2019] [Indexed: 02/09/2023]
Abstract
BACKGROUND We conducted a finite element study to assess the effectiveness of a novel pedicle screw design with two alterations in the distal and proximal portions. METHODS Finite element (FE) models of 24 vertebrae were constructed using computed tomographic data. Pull-out strength of 4 different pedicle screws were compared. The basic screw design was a dual threaded one (PS0), in which the proximal portion is double-threaded (cortical thread), and the distal portion is single-threaded (cancellous thread). In PS1, the inter-thread double-core shape was added to PS0 in the distal portion. Compared to PS0, in PS2, the proximal portion was elongated by 5 mm. PS3 had both PS1 and PS2 features. In addition, the 24 vertebrae were classified into 3 groups based on volumetric bone mineral density (vBMD) of the vertebral body: low <120 mg/cm3, moderate 120-170 mg/cm3, and high >170 mg/cm3. RESULTS The mean pull-out strengths (±SD) were 1137 ± 500 N, 1188 ± 520 N, 1191 ± 512 N, and 1242 ± 538 N for PS0, PS1, PS2, and PS3, respectively. In PS1, there was significant difference in the incremental ratio of pull-out strength to PS0 between the low and high vBMD groups (3.7 ± 1.6% vs. 5.0 ± 1.0%, p = 0.006). In PS2, there was a significant difference in the incremental ratio to PS0 between the moderate and high vBMD groups (7.6 ± 4.0% vs. 3.3 ± 1.8%, p < 0.001). In PS3, there was a significant difference in the incremental ratio to PS0 between the moderate and high vBMD groups (12.1 ± 4.8% vs. 8.5 ± 2.1%, p = 0.003). CONCLUSIONS The two design alterations showed the combined additive effect in the PS3 design. The moderate vBMD group has a balanced bone property to reflect the combined effects of the PS1 and PS2 design alterations.
Collapse
Affiliation(s)
- Shota Takenaka
- Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, Suita, Japan
| | - Takashi Kaito
- Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, Suita, Japan.
| | - Ken Ishii
- Department of Orthopedic Surgery, School of Medicine, International University of Health and Welfare, Chiba, Japan
| | - Kota Watanabe
- Department of Orthopedic Surgery, Keio University School of Medicine, Tokyo, Japan
| | - Kei Watanabe
- Department of Orthopaedic Surgery, Niigata University Medical and Dental Hospital, Niigata, Japan
| | - Akira Shinohara
- Department of Orthopaedic Surgery, The Jikei University School of Medicine, Tokyo, Japan
| | - Tomohisa Harada
- Department of Spinal Surgery, Rakuwakai Marutamachi Hospital, Kyoto, Japan
| | | | | | - Morio Matsumoto
- Department of Orthopedic Surgery, Keio University School of Medicine, Tokyo, Japan
| |
Collapse
|
|
27
|
Muramoto Y, Fridrici V, Kapsa P, Bouvard G, Ohta M. Effects of temperature increase during surgical drilling in acrylic resin. Technol Health Care 2019; 28:369-380. [PMID: 31796714 DOI: 10.3233/thc-191870] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
BACKGROUND Acrylic resin is employed for drilling bone biomodels. Since drilling causes temperature rise, the mechanical properties of thermoplastic acrylic resin can be altered, consequently affecting drilling properties. However, it is currently unclear how this temperature increase impacts drilling. OBJECTIVE This study reports the effects of temperature rise on both mechanical and drilling properties through experiments in which acrylic resin is drilled under machining conditions employed in surgical operations. METHODS Drilling tests were performed using a surgical drill on medical acrylic resin under dry conditions to observe generated cutting chips and measure drilling properties such as torque, drilling time, and temperature rise. Dynamic mechanical analysis measurements were performed to consider temperature effects. RESULTS According to the morphological classification of the cutting chips, the drilling process is divided into three phases corresponding with the generation of cylindrical helix, waved, and rounded nubby chips respectively. During drilling, the temperature of the chips can exceed the glass transition temperature (100∘C) resulting in decreased viscoelasticity, which is associated with decreased torque. CONCLUSIONS While drilling acrylic resin under surgical machining conditions, increasing temperature can decrease torque and morphologically change cutting chips due to the decrease in mechanical properties above the glass transition temperature.
Collapse
Affiliation(s)
- Y Muramoto
- Institute of Fluid Science, Tohoku University, Sendai, Miyagi, Japan.,Graduate School of Biomedical Engineering, Tohoku University, Sendai, Miyagi, Japan.,Laboratoire de Tribologie et Dynamique des Systèmes, UMR CNRS 5513, Ecole Centrale de Lyon, Université de Lyon, Ecully cedex, France
| | - V Fridrici
- Laboratoire de Tribologie et Dynamique des Systèmes, UMR CNRS 5513, Ecole Centrale de Lyon, Université de Lyon, Ecully cedex, France
| | - Ph Kapsa
- Laboratoire de Tribologie et Dynamique des Systèmes, UMR CNRS 5513, Ecole Centrale de Lyon, Université de Lyon, Ecully cedex, France
| | - G Bouvard
- Laboratoire de Tribologie et Dynamique des Systèmes, UMR CNRS 5513, Ecole Centrale de Lyon, Université de Lyon, Ecully cedex, France
| | - M Ohta
- Institute of Fluid Science, Tohoku University, Sendai, Miyagi, Japan.,ElyTMaX UMI 3757, CNRS - Université de Lyon - Tohoku University, International Joint Unit, Tohoku University, Sendai, Miyagi, Japan
| |
Collapse
|
|
28
|
Hollensteiner M, Esterer B, Fürst D, Schrempf A, Augat P. Development of open-cell polyurethane-based bone surrogates for biomechanical testing of pedicle screws. J Mech Behav Biomed Mater 2019; 97:247-253. [DOI: 10.1016/j.jmbbm.2019.05.038] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Revised: 05/14/2019] [Accepted: 05/14/2019] [Indexed: 11/29/2022]
|
|
29
|
Hsieh MK, Liu MY, Chen JK, Tsai TT, Lai PL, Niu CC, Tai CL. Biomechanical study of the fixation stability of broken pedicle screws and subsequent strategies. PLoS One 2019; 14:e0219189. [PMID: 31251780 PMCID: PMC6599116 DOI: 10.1371/journal.pone.0219189] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2019] [Accepted: 06/18/2019] [Indexed: 11/18/2022] Open
Abstract
Pedicles are often broken when screws are inserted into hard pedicles with small diameters or when the diameter of the screw itself is inadequate. However, there is a lack of biomechanical literature that addresses screw loosening as a result of broken pedicles or the resulting salvage of those screws. We performed a novel in vitro study to compare the pullout strength of screws between intact pedicles and two different types of broken pedicles; strategies to prevent screw loosening were also compared. Thirty L4 Sawbones were designed to represent intact pedicles, semi-pedicles, and nonpedicles and were prepared for screw insertion. Three sizes of polyaxial screws (diameter × length dimensions of 6.0 mm × 45 mm, 6.0 mm × 50 mm and 6.5 mm × 45 mm) were independently and randomly distributed into the intact-pedicle group (IP group, n = 30), the semi-pedicle group (SP group, n = 15), or the nonpedicle group (NP group, n = 15). The experiments were conducted across a minimum of five trials for each of the chosen screw sizes. We then analyzed the results of the imaging, pullout testing, and embedded bone volume. Any fractures or defects of the vertebrae caused by screw insertion were excluded from the study. The appropriate screw trajectory and insertional depth were confirmed using axial and sagittal X-ray imaging prior to screw pullout testing. A pullout strength of only 41% to 45% for the SP group and 29% to 39% for the NP group was retained following a broken pedicle. The use of longer or larger-diameter screws appears to be an effective salvaging procedure for the NP group (p < 0.05). The embedded bone volume percentage analysis indicated that, compared to the IP group, 68% to 76% of effective bone embedded into the screw threads in the SP group, and 58% to 65% in the NP group. There was no direct correlation between the pullout strength and the embedded bone volume; however, less effective embedded bone volume was associated with lower pullout strength. This study describes the evolution of the well-established screw pullout test being applied to the broken pedicle Sawbone testing model. The pedicle plays an important role in determining the pullout strength of a screw. However, a salvage procedure that utilizes a longer or larger-diameter screw might be a reliable clinical approach to address broken pedicles.
Collapse
Affiliation(s)
- Ming-Kai Hsieh
- Institute of Biotechnology, National Taiwan University, Taipei, Taiwan
- Bone and Joint Research Center, Chang Gung Memorial Hospital, Taoyuan, Taiwan
- Department of Orthopaedic Surgery, Spine Section, Chang Gung Memorial Hospital and College of Medicine, Chang Gung University, Taoyuan, Taiwan
| | - Mu-Yi Liu
- Ph.D. Program in Biomedical Engineering, Collage of Engineering, Chang Gung University, Taoyuan, Taiwan
| | - Jin-Kai Chen
- Graduate Institute of Biomedical Engineering, Chang Gung University, Taoyuan, Taiwan
| | - Tsung-Ting Tsai
- Bone and Joint Research Center, Chang Gung Memorial Hospital, Taoyuan, Taiwan
- Department of Orthopaedic Surgery, Spine Section, Chang Gung Memorial Hospital and College of Medicine, Chang Gung University, Taoyuan, Taiwan
| | - Po-Liang Lai
- Bone and Joint Research Center, Chang Gung Memorial Hospital, Taoyuan, Taiwan
- Department of Orthopaedic Surgery, Spine Section, Chang Gung Memorial Hospital and College of Medicine, Chang Gung University, Taoyuan, Taiwan
| | - Chi-Chien Niu
- Bone and Joint Research Center, Chang Gung Memorial Hospital, Taoyuan, Taiwan
- Department of Orthopaedic Surgery, Spine Section, Chang Gung Memorial Hospital and College of Medicine, Chang Gung University, Taoyuan, Taiwan
| | - Ching-Lung Tai
- Bone and Joint Research Center, Chang Gung Memorial Hospital, Taoyuan, Taiwan
- Department of Orthopaedic Surgery, Spine Section, Chang Gung Memorial Hospital and College of Medicine, Chang Gung University, Taoyuan, Taiwan
- Graduate Institute of Biomedical Engineering, Chang Gung University, Taoyuan, Taiwan
- * E-mail:
| |
Collapse
|
|
30
|
Kovacı H, Yetim AF, Çelik A. Biomechanical analysis of spinal implants with different rod diameters under static and fatigue loads: an experimental study. BIOMED ENG-BIOMED TE 2019; 64:339-346. [PMID: 29935109 DOI: 10.1515/bmt-2017-0236] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2017] [Accepted: 06/01/2018] [Indexed: 02/06/2023]
Abstract
Spinal implants are commonly used in the treatment of spinal disorders or injuries. However, the biomechanical analyses of them are rarely investigated in terms of both biomechanical and clinical perspectives. Therefore, the main purpose of this study is to investigate the effects of rod diameter on the biomechanical behavior of spinal implants and to make a comparison among them. For this purpose, three spinal implants composed of pedicle screws, setscrews and rods, which were manufactured from Ti6Al4V, with diameters of 5.5 mm, 6 mm and 6.35 mm were used and a bilateral vertebrectomy model was applied to spinal systems. Then, the obtained spinal systems were tested under static tension-compression and fatigue (dynamic compression) conditions. Also, failure analyses were performed to investigate the fatigue behavior of spinal implants. After static tension-compression and fatigue tests, it was found that the yield loads, stiffness values, load carrying capacities and fatigue performances of spinal implants enhanced with increasing spinal rod diameter. In comparison to spinal implants with 5.5 mm rods, the fatigue limits of implants showed 13% and 33% improvements in spinal implants having 6 mm and 6.35 mm rods, respectively. The highest static and fatigue test results were obtained from spinal implants having 6.35 mm rods among the tested implants. Also, it was observed that the increasing yield load and stiffness values caused an increase in the fatigue limits of spinal implants.
Collapse
Affiliation(s)
- Halim Kovacı
- Department of Mechanical Engineering, Engineering Faculty, Atatürk University, Erzurum 25240, Turkey
| | - Ali Fatih Yetim
- Department of Mechanical Engineering, Engineering and Architecture Faculty, Erzurum Technical University, Erzurum 25700, Turkey
| | - Ayhan Çelik
- Department of Mechanical Engineering, Engineering Faculty, Atatürk University, Erzurum 25240, Turkey
| |
Collapse
|
|
31
|
Pedicle Screw Designs in Spinal Surgery: Is There a Difference? A Biomechanical Study on Primary and Revision Pull-Out Strength. Spine (Phila Pa 1976) 2019; 44:E144-E149. [PMID: 30005047 DOI: 10.1097/brs.0000000000002789] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN An experimental laboratory-based biomechanical study. OBJECTIVE The objective of this study was to evaluate, in a synthetic bone model, the difference in primary and revision pull-out strength using pedicle screws of different thread designs. SUMMARY OF BACKGROUND DATA Over the past few decades, there has been a growing interest in optimizing the screw pull-out strength using various screw designs (single-thread, mixed-thread, dual-thread). Although primary pull-out strength has been studied previously, little is known about revision pull-out strength of different pedicle screws. METHODS The pull-out strengths of three different pedicle screw designs (single-thread, mixed-thread, dual-thread) were tested in standardized polyurethane foam in three sequences. Sequence 1: A 6.5 mm screw was inserted into the foam block and the primary pull-out strength measured. Sequence 2: A 6.5 mm screw was inserted, removed, and then reinserted into the same foam block. The revision pull-out strength was then measured. Sequence 3: A 6.5 mm screw was inserted, removed and a 7.5-mm screw of the same thread design was reinserted. The revision pull-out strength was then measured. RESULTS The primary pull-out strength was similar across screw designs, although dual-thread screws showed higher primary pull-out strength (2628.8 N) compared to single-thread screws (2184.4 N, P < 0.05). For revision pull-out strength, the mixed-thread screws had significant reduction in revision pull-out strength of 18.6% (1890.2 N, P = 0.0173). Revision with a larger diameter screw improved the pull-out strength back to baseline. Single and dual-thread screws showed no significant reduction in revision pull-out strength. CONCLUSION The dual-threaded screws provided the strongest primary pull-out strength for spinal fixation. The mixed-thread screws, however, had the poorest revision pull-out strength, decreasing by 18.6% compared to other screw designs. In cases in which mixed-threaded screws have to be revised (at the index or revision surgery), surgeons should consider the use of larger diameter screws to improve the pull-out strength. LEVEL OF EVIDENCE 5.
Collapse
|
|
32
|
Biswas JK, Sahu TP, Rana M, Roy S, Karmakar SK, Majumder S, Roychowdhury A. Design factors of lumbar pedicle screws under bending load: A finite element analysis. Biocybern Biomed Eng 2019. [DOI: 10.1016/j.bbe.2018.10.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
|
|
33
|
Toth JM, Wang M, Patel CK, Arora A. Early term effects of rhBMP-2 on pedicle screw fixation in a sheep model: histomorphometric and biomechanical analyses. JOURNAL OF SPINE SURGERY 2018; 4:534-545. [PMID: 30547116 DOI: 10.21037/jss.2018.06.19] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Background The effects of recombinant human bone morphogenetic protein-2 (rhBMP-2) on pedicle screw pullout force and its potential to improve spinal fixation have not previously been investigated. rhBMP-2 on an absorbable collagen sponge (ACS) carrier was delivered in and around cannulated and fenestrated pedicle screws in a sheep lumbar spine instability model. Two control groups (empty screw and ACS with buffer) were also evaluated. We hypothesized that rhBMP-2 could stimulate bone growth in and around the cannulated and fenestrated pedicle screws to improve early bone purchase. Methods Eight skeletally mature sheep underwent destabilizing laminectomies at L2-L3 and L4-L5 followed by stabilization with pedicle screw and rod constructs. An ACS carrier was used to deliver 0.15 mg of rhBMP-2 within and around the cannulated and fenestrated titanium pedicle screws. Biomechanics and histomorphometry were used to evaluate the early term results at 6 and 12 postoperative weeks. Results rhBMP-2 was unable to improve bony purchase of the cannulated and fenestrated pedicle screws compared to both control groups. Although rhBMP-2 groups had pullout forces that were less than both control groups, both rhBMP-2 groups had pullout force values exceeding 2,000 N, which was comparable to previously published results for unmodified pedicle screws. Significant differences in the percentages of bone in peri-screw tissues was not observed amongst the four treatment groups. Microradiography and quantitative histomorphometry showed that at 6 weeks, rhBMP-2 induced peri-screw remodeling regions containing peri-implant bone which was hypodense with respect to surrounding native trabeculae. A moderate correlation between biomechanical pullout variables and histomorphometry data was observed. Conclusions The design of the cannulated and fenestrated pedicle screw was able to facilitate new bone formation to achieve high pullout forces. However, delivery of rhBMP-2 should be carefully controlled to prevent excessive bone remodeling which could cause early screw loosening.
Collapse
Affiliation(s)
- Jeffrey M Toth
- Department of Orthopaedic Surgery, The Medical College of Wisconsin Inc., Milwaukee, WI, USA.,Orthopaedic & Rehabilitation Engineering Center and Graduate Program in Dental Biomaterials, Marquette University, Milwaukee, WI, USA
| | - Mei Wang
- Department of Orthopaedic Surgery, The Medical College of Wisconsin Inc., Milwaukee, WI, USA.,Orthopaedic & Rehabilitation Engineering Center and Graduate Program in Dental Biomaterials, Marquette University, Milwaukee, WI, USA
| | - Chetan K Patel
- Spine Health Institute, Florida Hospital Medical Group, Altamonte Springs, FL, USA
| | - Akshi Arora
- Orthopaedic & Rehabilitation Engineering Center and Graduate Program in Dental Biomaterials, Marquette University, Milwaukee, WI, USA
| |
Collapse
|
|
34
|
Novel Placement of Cortical Bone Trajectory Screws in the Lumbar Spine: A Radiographic and Cadaveric Study. Clin Spine Surg 2018; 31:E329-E336. [PMID: 29782335 DOI: 10.1097/bsd.0000000000000651] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
STUDY DESIGN This is a radiographic and cadaveric study. OBJECTIVE The aim of this study was to conduct a detailed comparison about the parameters between the ideal cortical bone trajectory (CBT) and practical CBT screw. SUMMARY OF BACKGROUND DATA CBT screws have recently become popular in spinal surgery, mainly because of their improved fixation while minimizing soft tissue dissection. However, to our knowledge, no previous study has provided a detailed comparison on the parameters between the ideal CBT and practical CBT screws. MATERIALS AND METHODS The 3-dimensional computed tomography scans of 126 spinal vertebrae separated from 40 lumbar spines were studied. After determining the CBT, the maximal screw length, maximal screw diameter, lateral angle (LA), and cephalad angle (CA) were calculated. Thereafter, CBT screws were inserted into these cadaveric lumbar spines. Subsequently, the lateral angle of screw (LAs) and cephalad angle of screw (CAs) of the screws were measured using 3-dimensional computed tomography. RESULTS As for the ideal CBT, the maximal screw length gradually increased from L1 (32.0 mm) to L4 (35.3 mm) and then decreased at L5 (34.8 mm). Moreover, the maximal screw diameter increased from L1 (4.5 mm) to L5 (7.5 mm). The LA from L1 to L5 were 9.2, 9.4, 9.9, 11.2, and 12.0 degrees, respectively. The CA from L1 to L5 were 25.8, 25.8, 26.3, 26.8, and 26.0 degrees, respectively. As for the actual CBT screw, the LAs from L1 to L5 were 12.7, 14.1, 13.2, 12.4, and 13.0 degrees, respectively. The CAs from L1 to L5 were 25.4, 27.5, 29.2, 30.1, and 30.5 degrees, respectively. Significant differences were observed between the angles of the ideal trajectory and the actual screw. CONCLUSIONS Parameters of the actual CBT screw are slightly larger than the optimal trajectory measurements. The CAs and LAs are ∼25-30 and 10-16 degrees, respectively. L1 and L2 should be given considerable attention when using the CBT technique. And the trajectory measurements can only be used as a guide in clinical practice.
Collapse
|
|
35
|
Lai DM, Shih YT, Chen YH, Chien A, Wang JL. Effect of pedicle screw diameter on screw fixation efficacy in human osteoporotic thoracic vertebrae. J Biomech 2018; 70:196-203. [DOI: 10.1016/j.jbiomech.2017.10.009] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Revised: 08/19/2017] [Accepted: 10/15/2017] [Indexed: 11/27/2022]
|
|
36
|
Nagaraja S, Palepu V. Comparisons of Anterior Plate Screw Pullout Strength Between Polyurethane Foams and Thoracolumbar Cadaveric Vertebrae. J Biomech Eng 2017; 138:2545528. [PMID: 27536905 DOI: 10.1115/1.4034427] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Indexed: 12/20/2022]
Abstract
Synthetic polyurethane foams are frequently used in biomechanical testing of spinal medical devices. However, it is unclear what types of foam are most representative of human vertebral trabecular bone behavior, particularly for testing the bone-implant interface. Therefore, a study was conducted to compare polyurethane foam microstructure and screw pullout properties to human vertebrae. Cadaveric thoracolumbar vertebrae underwent microcomputed tomography to assess trabecular bone microstructure. Spine plate screws were implanted into the vertebral body and pullout testing was performed. The same procedure was followed for eight different densities (grades 5-30) of commercially available closed cell (CCF) and open cell foams (OCF). The results indicated that foam microstructural parameters such as volume fraction, strut thickness, strut spacing, and material density rarely matched that of trabecular bone. However, certain foams provided mechanical properties that were comparable to the cadavers tested. Pullout force and work to pullout for screws implanted into CCF grade 5 were similar to osteoporotic female cadavers. In addition, screw pullout forces and work to pullout in CCF grade 8, grade 10, and OCF grade 30 were similar to osteopenic male cadavers. All other OCF and CCF foams possessed pullout properties that were either significantly lower or higher than the cadavers tested. This study elucidated the types and densities of polyurethane foams that can represent screw pullout strength in human vertebral bone. Synthetic bone surrogates used for biomechanical testing should be selected based on bone quantity and quality of patients who may undergo device implantation.
Collapse
|
|
37
|
Albanese K, Ordway NR, Albanese SA, Lavelle WF. Effect of Pedicle Fill on Axial Pullout Strength in Spinal Fixation After Rod Reduction. Orthopedics 2017; 40:e990-e995. [PMID: 28968476 DOI: 10.3928/01477447-20170925-02] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Accepted: 08/08/2017] [Indexed: 02/03/2023]
Abstract
Rod reduction to pedicle screws is used for a variety of spinal fixation procedures; however, it can alter the integrity of the screw-bone interface. The authors investigated the effect of pedicle fill (ratio of pedicle screw diameter to pedicle diameter) on the strength of the screw-bone interface after simulated rod reduction on 17 vertebrae (3 thoracolumbar spine specimens). Pedicle diameter was measured with standard clinical computed tomography scan protocols. The authors determined the minimum pedicle diameter for each level. Polyaxial pedicle screws were surgically placed bilaterally with a freehand technique with standard clinical anatomic landmarks. The pedicle pairs were instrumented with pedicle screws of predetermined diameter, 1 with greater than 80% fill and 1 with less than 80% fill. A simulated reduction maneuver was performed with a 5-mm gap followed by an axial pullout test to assess screw interface strength. Comparison of insertion torque between less than 80% fill and greater than 80% fill did not show significant increases. A significant difference in pullout load (P=.043) occurred with greater than 80% fill (791±637 N) compared with less than 80% fill (636±492 N). No significant difference in stiffness was noted (P=.154) with pedicle fill of greater than 80% (427±134 N/mm) compared with less than 80% (376±178 N/mm). The current findings support the use of greater than 80% pedicle fill for optimal screw anchoring in pedicle screw-based constructs involving rod reduction. Surgeons should consider placing screws that can safely fill vertebral pedicles, especially at the apex of the curve and the proximal and distal levels of constructs, where excessive forces are imparted to the screws. [Orthopedics. 2017; 40(6):e990-e995.].
Collapse
|
|
38
|
Comparison of Pedicle Screw Fixation Strength Among Different Transpedicular Trajectories: A Finite Element Study. Clin Spine Surg 2017; 30:301-307. [PMID: 28746125 DOI: 10.1097/bsd.0000000000000258] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
STUDY DESIGN Comparative biomechanical study by finite element (FE) method. OBJECTIVE To investigate the pullout strength of pedicle screws using different insertional trajectories. SUMMARY OF BACKGROUND DATA Pedicle screw fixation has become the gold standard for spinal fusion, however, not much has been done to clarify how the fixation strength of pedicle screws are affected by insertional trajectories and bone properties. MATERIALS AND METHODS Three-dimensional FE models of 20 L4 vertebrae were constructed from the computed tomographic data. Five different transpedicular trajectories were compared: the traditional trajectory, the vertical trajectory, and the 3 lateral trajectories with different sagittal directions (caudal, parallel, cranial). For a valid comparison, screws of the same shape and size were inserted into the same pedicle in each subject, and the pullout strength were compared with nonlinear FE analyses. In addition, the pullout strength was correlated with bone mineral density (BMD). RESULTS The mean pullout strength showed a 3.9% increase for the vertical trajectory relative to the traditional trajectory, 6.1% for the lateral-caudal trajectory, 21.1% for the lateral-parallel trajectory, and 34.7% for the lateral-cranial trajectory. The lateral-cranial trajectory demonstrated the highest value among all trajectories (P<0.001). In each trajectory, the correlation coefficient between the pullout strength and BMD of the femoral neck (r=0.74-0.83, P<0.01) was higher than the mean BMD of all the lumbar vertebrae (r=0.49-0.75, P<0.01), BMD of the L4 vertebra (r=0.39-0.64, P<0.01), and regional BMD of the L4 pedicle (r=0.53-0.76, P<0.01). CONCLUSIONS Regional variation in the vertebral bone density and the amount of denser bone-screw interface contribute to the differences of stiffness among different screw trajectories. BMD of the femoral neck is considered to be a better objective predictor of pedicle screw stability than that of the lumbar vertebra.
Collapse
|
|
39
|
Pelletier MH, Bertollo N, Al-Khawaja D, Walsh WR. The contribution of the cortical shell to pedicle screw fixation. JOURNAL OF SPINE SURGERY 2017; 3:184-192. [PMID: 28744499 DOI: 10.21037/jss.2017.06.07] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
BACKGROUND A pedicle screw insertion technique known as "hubbing" involves the removal of cortical bone around the screw insertion with the aim of improving fixation and decreasing screw loosening. However, the efficacy of this procedure relative to bone density and early loading have not been fully explored. The purpose of this study is to establish the contribution of the cortical layer (hubbing), cancellous density, early loading (toggling) in an idealised model. This is an in vitro laboratory study. METHODS Synthetic bone blocks with cancellous bulk and a simulated cortical shell were implanted with 6.5 mm pedicle screws. Three key variables were evaluated in this study; density of the simulated bone (10-20 lb/ft3), toggling (±0.5 mm for 10,000 cycles), and the presence or absence of the surrounding cortex (hubbing). Pullout testing after toggling was performed to determine maximum load, stiffness and energy. Results were analyzed to assess interaction and main effects. RESULTS Removal of the cortex decreased the pullout loads by approximately 1,100 N after toggling. Toggling in the presence of the cortical shell had no effect. However, once the cortical shell is removed damage to the weaker cancellous bone accumulates and further compromises the fixation. CONCLUSIONS The addition of a cortical layer in the Sawbone model is significant and provides a more realistic model of load sharing. The cortex plays a considerable role in the protection of underlying cancellous bone as well as contributing to initial pullout strength. The results of this study demonstrate a negative synergistic effect when both toggling and hubbing are applied to the weaker bone.
Collapse
Affiliation(s)
- Matthew Henry Pelletier
- Surgical & Orthopaedic Research Laboratories, Prince of Wales Clinical School, UNSW Australia, Prince of Wales Hospital, Sydney, NSW 2031, Australia
| | - Nicky Bertollo
- Surgical & Orthopaedic Research Laboratories, Prince of Wales Clinical School, UNSW Australia, Prince of Wales Hospital, Sydney, NSW 2031, Australia
| | - Darweesh Al-Khawaja
- Department of Neurosurgery, Wollongong Hospital, Wollongong, New South Wales 2500, Australia
| | - William Robert Walsh
- Surgical & Orthopaedic Research Laboratories, Prince of Wales Clinical School, UNSW Australia, Prince of Wales Hospital, Sydney, NSW 2031, Australia
| |
Collapse
|
|
40
|
Biomechanical arrangement of threaded and unthreaded portions providing holding power of transpedicular screw fixation. Clin Biomech (Bristol, Avon) 2016; 39:71-76. [PMID: 27693563 DOI: 10.1016/j.clinbiomech.2016.09.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Revised: 09/19/2016] [Accepted: 09/22/2016] [Indexed: 02/07/2023]
Abstract
BACKGROUND Failure of pedicle screw is a major concern in spinal surgery. The threaded and unthreaded portions of the pedicle screw provide the ability to anchor and squeeze the surrounding bone, respectively. This study aimed to investigate the anchoring and squeezing effects of different design of the threaded/unthreaded portions of a pedicle screw to vertebrae. METHODS Four variations (one fully and three partially threaded, with a 1/3, 1/2, and 2/3 unthreaded designs at the proximal portion) of screws were used to measure pullout strength and withdrawn energy using synthetic and porcine specimens. The tests were conducted in static and dynamic fashions, in that the screws were axially extracted directly and after 150,000cycles of lateral bending. The load-displacement curves were recorded to gain insight into the peak load (pullout strength) and cumulative work (withdrawn energy). FINDINGS The two testing results of the synthetic and porcine specimens consistently showed that the 1/3 unthreaded screw provides significantly higher pullout strength and withdrawn energy than the fully threaded screw. The withdrawn energy of the three unthreaded screws was significantly higher than that of the threaded counterpart. INTERPRETATION The holding power of a pedicle screw was the integration of the anchoring (cancellous core) and squeezing (compact pedicle) effects within the threaded and unthreaded portions. The current study recommends the 1/3 unthreaded screw as an optimal alternative for use as a shank-sliding mechanism to preserve the holding power within the pedicle isthmus.
Collapse
|
|
41
|
Prasad V, Mesfin A, Lee R, Reigrut J, Schmidt J. Probing and Tapping: Are We Inserting Pedicle Screws Correctly? Spine Deform 2016; 4:395-399. [PMID: 27927567 DOI: 10.1016/j.jspd.2016.06.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/10/2014] [Revised: 05/25/2016] [Accepted: 06/11/2016] [Indexed: 10/20/2022]
Abstract
PURPOSE Although there are a significant number of research publications on the topic of bone morphology and the strength of bone, the clinical significance of a failed pedicle screw is often revision surgery and the potential for further postoperative complications; especially in elderly patients with osteoporotic bone. The purpose of this report is to quantify the mechanical strength of the foam-screw interface by assessing probe/pilot hole diameter and tap sizes using statistically relevant sample sizes under highly controlled test conditions. METHODS The study consisted of two experiments and used up to three different densities of reference-grade polyurethane foam (ASTM 1839), including 0.16, 0.24, and 0.32 g/cm3. All screws and rods were provided by K2M Inc. and screws were inserted to a depth of 25 mm. A series of pilot holes, 1.5, 2.2, 2.7, 3.2, 3.7, 4.2, 5.0, and 6.0 mm in diameter were drilled through the entire depth of the material. A 6.5 × 45-mm pedicle screw was inserted and axially pulled from the material (n = 720). A 3.0-mm pilot hole was drilled and tapped with: no tap, 3.5-, 4.5-, 5.5-, and 6.5-mm taps. A 6.5 × 45-mm pedicle screw was inserted and axially pulled from the material (n = 300). RESULTS The size of the probe/pilot hole had a nonlinear, parabolic effect on pullout strength. This shape suggests an optimum-sized probe hole for a given size pedicle screw. Too large or too small of a probe hole causes a rapid falloff in pullout strength. The tap data demonstrated that not tapping and undertapping by two or three sizes did not significantly alter the pullout strength of the screws. The data showed an exponential falloff of pullout strength when as tap size increased to the diameter of the screw. CONCLUSION In the current study, the data show that an ideal pilot hole size half the diameter of the screw is a starting point. Also, that if tapping was necessary, to use a tap two sizes smaller than the screw being implanted. A similar optimum pilot hole or tap size may be expected in the clinical scenario, however, it may not be the same as seen with the uniform density polyurethane foam tested in the current study.
Collapse
Affiliation(s)
- Vishal Prasad
- Medway Maritime Hospital, NHS Foundation Trust, Gillingham, Kent, United Kingdom
| | - Addisu Mesfin
- Department of Orthopaedics and Rehabilitation, University of Rochester, Rochester, NY, USA
| | - Robert Lee
- Royal National Orthopaedic Hospital NHS Trust, Brockley Hill, Stanmore, Middlesex HA7 4LP, United Kingdom
| | | | - John Schmidt
- K2M Inc., 751 Miller Drive, Leesburg, VA 20175, USA.
| |
Collapse
|
|
42
|
A pedicle screw system and a lamina hook system provide similar primary and long-term stability: a biomechanical in vitro study with quasi-static and dynamic loading conditions. EUROPEAN SPINE JOURNAL : OFFICIAL PUBLICATION OF THE EUROPEAN SPINE SOCIETY, THE EUROPEAN SPINAL DEFORMITY SOCIETY, AND THE EUROPEAN SECTION OF THE CERVICAL SPINE RESEARCH SOCIETY 2016; 25:2919-28. [PMID: 27405823 DOI: 10.1007/s00586-016-4679-x] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Revised: 05/04/2016] [Accepted: 06/21/2016] [Indexed: 12/31/2022]
Abstract
PURPOSE For the stabilization of the thoracolumbar spine area, various stabilization techniques have been developed in recent decades. The aim of these techniques is to immobilize the treated segment to repositioning or correct the spine and guaranty long-term stability to achieve a reliable fusion. The aim of this study was to simulate in an in vitro experiment the postoperative long-term situation in elderly osteoporotic patients to compare two different stabilization principles; a pedicle screw system and a lamina hook system. METHODS Two comparable groups with respect to age and bone mineral density with each n = 6 fresh-frozen human, bi-segmental thoracolumbar spine specimens (T11-L1) were used. Antero-posterior and lateral radiographs were taken before the test, to assess the spinal status. Then the intact specimens were biomechanically characterized with pure moments in the three anatomical planes in different states in terms of range of motion and neutral zone. After implantation of either, a pedicle screw system or a lamina hook system, the primary stability was determined under the same conditions. Subsequently the specimens were cyclically loaded under complex loading, using a custom-made set-up in a dynamic materials testing machine with increasing moments from 3 to 66 Nm until 100,000 cycles or until one of the three defined "failure" criteria was reached. (1) A failure of a bony structure. (2) Exceeding of the threefold ROM of the primary stability after implantation in flexion plus extension. (3) Reaching of the ROM based on the intact state before implantation both in flexion plus extension. RESULTS The results showed that the ROM was strongly reduced after instrumentation similar for both implant systems in all motion planes. The highest stabilization was found in flexion/extension. During cyclic loading with increasing moments, the ROM increased continuously for both systems. The number of load cycles until one of the failure criteria was reached varied only slightly between the two groups. In the pedicle screw group 30,000 (median) loading cycles (range 5000-80,000) with a corresponding moment of 24 Nm (range 9-54) could be reached. In the lamina hook group 32,500 load cycles (range 20,000-45,000) could be achieved with a corresponding moment of 25.5 Nm (range 18-33). There was a slight trend that the pedicle screw system is influenced more by bone mineral density. CONCLUSION Both implant systems provide similar primary stability and similar long-term stability. In the pedicle screw group, there was a stronger correlation between bone mineral density and the reached number of load cycles.
Collapse
|
|
43
|
Tai CL, Tsai TT, Lai PL, Chen YL, Liu MY, Chen LH. A Biomechanical Comparison of Expansive Pedicle Screws for Severe Osteoporosis: The Effects of Screw Design and Cement Augmentation. PLoS One 2015; 10:e0146294. [PMID: 26720724 PMCID: PMC4697834 DOI: 10.1371/journal.pone.0146294] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2015] [Accepted: 12/15/2015] [Indexed: 01/18/2023] Open
Abstract
Expansive pedicle screws significantly improve fixation strength in osteoporotic spines. However, the previous literature does not adequately address the effects of the number of lengthwise slits and the extent of screw expansion on the strength of the bone/screw interface when expansive screws are used with or without cement augmentation. Herein, four designs for expansive pedicle screws with different numbers of lengthwise slits and different screw expansion levels were evaluated. Synthetic bones simulating severe osteoporosis were used to provide a comparative platform for each screw design. The prepared specimens were then tested for axial pullout failure. Regardless of screw design, screws with cement augmentation demonstrated significantly higher pullout strength than pedicle screws without cement augmentation (p < 0.001). For screws without cement augmentation, solid screws exhibited the lowest pullout strength compared to the four expansive groups (p < 0.01). No significant differences in pullout strength were observed between the expansive screws with different designs (p > 0.05). Taken together, our results show that pedicle screws combined with cement augmentation may greatly increase screw fixation regardless of screws with or without expansion. An increase in both the number of slits and the extent of screw expansion had little impact on the screw-anchoring strength. Cement augmentation is the most influential factor for improving screw pullout strength.
Collapse
Affiliation(s)
- Ching-Lung Tai
- Graduate Institute of Medical Mechatronics, Department of Mechanical Engineering, Chang Gung University, Kweishan, Taoyuan, Taiwan
| | - Tsung-Ting Tsai
- Department of Orthopedic Surgery, Bone and Joint Research Center, Chang Gung Memorial Hospital, Chang Gung University College of Medicine, Kweishan, Taoyuan, Taiwan
| | - Po-Liang Lai
- Department of Orthopedic Surgery, Bone and Joint Research Center, Chang Gung Memorial Hospital, Chang Gung University College of Medicine, Kweishan, Taoyuan, Taiwan
| | - Yi-Lu Chen
- Graduate Institute of Medical Mechatronics, Department of Mechanical Engineering, Chang Gung University, Kweishan, Taoyuan, Taiwan
| | - Mu-Yi Liu
- Graduate Institute of Medical Mechatronics, Department of Mechanical Engineering, Chang Gung University, Kweishan, Taoyuan, Taiwan
| | - Lih-Huei Chen
- Department of Orthopedic Surgery, Bone and Joint Research Center, Chang Gung Memorial Hospital, Chang Gung University College of Medicine, Kweishan, Taoyuan, Taiwan
- * E-mail:
| |
Collapse
|
|
44
|
Tolunay T, Başgül C, Demir T, Yaman ME, Arslan AK. Pullout performance comparison of pedicle screws based on cement application and design parameters. Proc Inst Mech Eng H 2015; 229:786-93. [DOI: 10.1177/0954411915612494] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Pedicle screws are the main fixation devices for certain surgeries. Pedicle screw loosening is a common problem especially for osteoporotic incidents. Cannulated screws with cement augmentation are widely used for that kind of cases. Dual lead dual cored pedicle screw has already given promising pullout values without augmentation. This study concentrates on the usage of dual lead dual core with cement augmentation as an alternative to cannulated and standard pedicle screws with cement augmentation. Five groups (dual lead dual core, normal pedicle screw and cannulated pedicle screw with augmentation, normal pedicle screw, dual lead dual cored pedicle screw) were designed for this study. Healthy bovine vertebrae and synthetic polyurethane foams (grade 20) were used as embedding test medium. Test samples were prepared in accordance with surgical guidelines and ASTM F543 standard testing protocols. Pullout tests were conducted with Instron 3300 testing frame. Load versus displacement values were recorded and maximum pullout loads were stated. The dual lead dual cored pedicle screw with poly-methyl methacrylate augmentation exhibited the highest pullout values, while dual lead dual cored pedicle screw demonstrated similar pullout strength as cannulated pedicle screw and normal pedicle screw with poly-methyl methacrylate augmentation. The dual lead dual cored pedicle screw with poly-methyl methacrylate augmentation can be used for osteoporotic and/or severe osteoporotic patients according to its promising results on animal cadaver and synthetic foams.
Collapse
Affiliation(s)
- Tolga Tolunay
- Department of Orthopaedics, Yenimahalle Education and Research Hospital, Ankara, Turkey
| | - Cemile Başgül
- Department of Mechanical Engineering, TOBB University of Economics and Technology, Ankara, Turkey
| | - Teyfik Demir
- Department of Mechanical Engineering, TOBB University of Economics and Technology, Ankara, Turkey
| | - Mesut E Yaman
- Department of Neurosurgery, Yenimahalle Education and Research Hospital, Ankara, Turkey
| | - Arslan K Arslan
- Department of Orthopaedics, Yenimahalle Education and Research Hospital, Ankara, Turkey
| |
Collapse
|
|
45
|
Matsukawa K, Yato Y, Imabayashi H, Hosogane N, Asazuma T, Nemoto K. Biomechanical evaluation of the fixation strength of lumbar pedicle screws using cortical bone trajectory: a finite element study. J Neurosurg Spine 2015; 23:471-8. [DOI: 10.3171/2015.1.spine141103] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
OBJECT
Cortical bone trajectory (CBT) maximizes thread contact with the cortical bone surface and provides increased fixation strength. Even though the superior stability of axial screw fixation has been demonstrated, little is known about the biomechanical stiffness against multidirectional loading or its characteristics within a unit construct. The purpose of the present study was to quantitatively evaluate the anchorage performance of CBT by the finite element (FE) method.
METHODS
Thirty FE models of L-4 vertebrae from human spines (mean age [± SD] 60.9 ± 18.7 years, 14 men and 16 women) were computationally created and pedicle screws were placed using the traditional trajectory (TT) and CBT. The TT screw was 6.5 mm in diameter and 40 mm in length, and the CBT screw was 5.5 mm in diameter and 35 mm in length. To make a valid comparison, the same shape of screw was inserted into the same pedicle in each subject. First, the fixation strength of a single pedicle screw was compared by axial pullout and multidirectional loading tests. Next, vertebral fixation strength within a construct was examined by simulating the motions of flexion, extension, lateral bending, and axial rotation.
RESULTS
CBT demonstrated a 26.4% greater mean pullout strength (POS; p = 0.003) than TT, and also showed a mean 27.8% stronger stiffness (p < 0.05) during cephalocaudal loading and 140.2% stronger stiffness (p < 0.001) during mediolateral loading. The CBT construct had superior resistance to flexion and extension loading and inferior resistance to lateral bending and axial rotation. The vertebral fixation strength of the construct was significantly correlated with bone mineral density of the femoral neck and the POS of a single screw.
CONCLUSIONS
CBT demonstrated superior fixation strength for each individual screw and sufficient stiffness in flexion and extension within a construct. The TT construct was superior to the CBT construct during lateral bending and axial rotation.
Collapse
Affiliation(s)
- Keitaro Matsukawa
- 1Department of Orthopaedic Surgery, National Defense Medical College, Tokorozawa, Saitama; and
| | - Yoshiyuki Yato
- 2Department of Orthopaedic Surgery, National Hospital Organization, Murayama Medical Center, Musashimurayama, Tokyo, Japan
| | - Hideaki Imabayashi
- 1Department of Orthopaedic Surgery, National Defense Medical College, Tokorozawa, Saitama; and
| | - Naobumi Hosogane
- 1Department of Orthopaedic Surgery, National Defense Medical College, Tokorozawa, Saitama; and
| | - Takashi Asazuma
- 2Department of Orthopaedic Surgery, National Hospital Organization, Murayama Medical Center, Musashimurayama, Tokyo, Japan
| | - Koichi Nemoto
- 1Department of Orthopaedic Surgery, National Defense Medical College, Tokorozawa, Saitama; and
| |
Collapse
|
|
46
|
Mehmanparast HN, Mac-Thiong JM, Petit Y. Biomechanical evaluation of pedicle screw loosening mechanism using synthetic bone surrogate of various densities. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2015; 2014:4346-9. [PMID: 25570954 DOI: 10.1109/embc.2014.6944586] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Pedicle screw fixation is a well-established procedure for various spinal disorders. However, pedicle screws failures are still reported. Therefore, there is a need for a greater understanding of the pedicle screw failure mechanism. This experimental study investigates the biomechanical stability of pedicle screws using a synthetic bone surrogate with a special focus on the screw loosening mechanism. Pedicle screws have been inserted in thirty six polyurethane foam blocks of three different densities. In half of the specimens from each density group, pedicle screws were submitted to cyclic bending (toggling) before pullout. The rest of specimens were solely loaded in axial pullout. The peak pullout force and stiffness were determined from load-displacement curve of each specimen. Statistical analyses were performed to investigate on the effect of toggling and bone surrogate density on the pedicle screw's pullout force. The results suggest that the pullout force and stiffness were significantly affected by toggling and density. Higher pullout forces resulted from higher grades of density. The proposed method allowed investigating the pedicle screw loosening mechanism. However, conducing further experimental tests on animal or cadaveric vertebrae are needed to confirm these findings.
Collapse
|
|
47
|
Evaluation of the Fixation Strength of Pedicle Screws Using Cortical Bone Trajectory: What Is the Ideal Trajectory for Optimal Fixation? Spine (Phila Pa 1976) 2015. [PMID: 26222663 DOI: 10.1097/brs.0000000000000983] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN In vivo analysis of insertional torque of pedicle screws using cortical bone trajectory (CBT) technique. OBJECTIVE To investigate factors contributing to the fixation strength of CBT screws and to clarify the ideal cortical trajectory for lumbar fusion. SUMMARY OF BACKGROUND DATA CBT has developed as a new minimally invasive technique of lumbar instrumentation. Despite biomechanical studies demonstrating the superior characteristics of CBT, no study has elucidated the most suitable path for optimal fixation or compared the fixation within variations of trajectory. METHODS The insertional torque of pedicle screws using CBT was measured intraoperatively in 72 consecutive patients. The detailed positions of a total of 268 screws were confirmed using postoperative reconstruction computed tomographic scans and were analyzed to identify factors contributing to the level of insertional torque. Investigated factors were as follows: (1) age, (2) bone mineral density of the femoral neck and lumbar vertebrae by dual-energy x-ray absorptiometry; (3) the pedicle width and height, (4) the length of the implant, (5) total screw length within the vertebra, (6) the screw length within the vertebral body, (7) the screw length within the lamina, (8) the cephalad and lateral angle of the trajectory, and (9) the distance from the long axis of the screw to the inferior and medial borders of the pedicle. RESULTS Multiple regression analysis showed that bone mineral density of the femoral neck, screw length within the lamina, and cephalad angle were significant independent factors affecting torque. CONCLUSION The fixation of CBT screws varied depending on technical factors (cephalad angle and screw length within the lamina) as well as the individual patient factor of bone mineral density. The ideal trajectory was directed 25° to 30° cranially along the inferior border of the pedicle so as to obtain maximum contact with the lamina and sufficient length within the vertebral body. LEVEL OF EVIDENCE 2.
Collapse
|
|
48
|
Tolunay T, Arslan K, Yaman O, Dalbayrak S, Demir T. Biomechanical Performance of Various Cement-Augmented Cannulated Pedicle Screw Designs for Osteoporotic Bones. Spine Deform 2015; 3:205-210. [PMID: 27927460 DOI: 10.1016/j.jspd.2014.09.055] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/03/2014] [Revised: 09/12/2014] [Accepted: 09/17/2014] [Indexed: 10/23/2022]
Abstract
INTRODUCTION Early-stage pullout is a common problem for surgeons during the fixation of osteoporotic bones. Poor bone quality limits the use of pedicle screws for patients with osteoporosis. In this study, the researchers investigated the effects of hole and gap position and type on the pullout strength of cannulated screws. METHODS Seven different designs were tested, including a control group. All cannula diameters were 2 mm and holes were drilled with a diameter of 1.5 mm. Gaps were milled with a 2-mm-diameter tool with 2-mm displacement proximally. All holes and gaps were drilled or opened unilaterally and bilaterally. Grade 40 and 10 polyurethane foam was used to simulate healthy and osteoporotic bones, respectively. For pullout tests, insertion depth was 30 mm and 2-mm-diameter pilot holes were drilled into blocks before screws were inserted. The cross-head speed was 2 mm/min. For torsion tests, 1 side of the screw was fixed and other was twisted clockwise. RESULTS For torsion tests, the maximum torque value exhibited by the control group (non-cannulated) was 14.94 Nm. The highest torsional strength among tested cannulated screws was 13.54 Nm for Single side two holes including design (S2H) (p < .0001). The minimum torsional strength was 9.45 Nm with a breaking angle of 39° (p < .005). Comparing results for samples pulled out from grade 40 polyurethane foam, single side slot including design (SS) samples exhibited the highest pullout strength with a maximum force of 3,104 N. CONCLUSIONS The unilateral, sequential, 3-radial hole, drilled, cannulated screw was the optimal alternative when considering pullout and torsional strength as criteria.
Collapse
Affiliation(s)
- Tolga Tolunay
- Department of Orthopaedics, Yenimahalle Training and Research Hospital, 2026. Avenue, 06370, Ankara, Turkey
| | - Kağan Arslan
- Department of Orthopaedics, Yenimahalle Training and Research Hospital, 2026. Avenue, 06370, Ankara, Turkey
| | - Onur Yaman
- Department of Mechanical Engineering, TOBB University of Economics and Technology, Sogutozu Avenue, 06560, Ankara, Turkey
| | - Sedat Dalbayrak
- Department of Neurosurgery, Neurospinal Academy, Istanbul, Turkey
| | - Teyfik Demir
- Department of Mechanical Engineering, TOBB University of Economics and Technology, Sogutozu Avenue, 06560, Ankara, Turkey.
| |
Collapse
|
|
49
|
Mehmanparast HN, Mac-Thiong JM, Petit Y. Estimation of pedicle screw fixation strength from probe indentation force and screw insertion torque: a biomechanical study on bone surrogates of various densities. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2015; 2014:4350-3. [PMID: 25570955 DOI: 10.1109/embc.2014.6944587] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Posterior pedicle screw fixation is commonly used for patients with spinal disorders. However, failure of fixation is reported in many cases and surgeons have only little information. The objective of this study was to assess the correlation between the probe indentation force, screw insertion torque and the pullout force using bone surrogates of different densities. The indentation force and insertion torque were measured using a custom made test bench during screw insertion into polyurethane foam blocks. The two variables were significantly correlated to pullout force and to density. A high correlation was also found between indentation force and the peak insertion torque. The proposed methods for measuring indentation force and screw insertion torque were reproducible. This study suggests that the peak screw insertion torque and the indentation force can predict the screw fixation strength in synthetic bone models. Additional tests should be performed on animal and human specimens to confirm and to translate these findings to clinical applications.
Collapse
|
|
50
|
Pullout strength of thoracic pedicle screws improved with cortical bone ratio: a cadaveric study. J Orthop Sci 2014; 19:900-6. [PMID: 25100570 DOI: 10.1007/s00776-014-0614-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/02/2014] [Accepted: 07/14/2014] [Indexed: 02/09/2023]
Abstract
BACKGROUND The application of pedicle screw constructs for the osteoporotic vertebrae remains a serious clinical challenge for spinal surgeons and has been intensely studied recently. However, the exact role of the pedicular cortical bone composition and the screw-bone gap on the screw fixation failure has yet to be quantitatively documented. The current study aims to address this gap in our knowledge and elucidate possible relationships. METHODS Twelve fresh-frozen human cadaveric thoracic spine vertebrae (T9-T12) were harvested from six human cadavers (five males; one female; 63.5 ± 17 years). A three-dimensional reconstruction of the individual vertebrae was firstly rendered from computed tomography (CT) scan images to allow calculation of the cortical bone ratio. Specimens were then subdivided into three groups: Intact, 1-mm screw-bone gap, and 2-mm screw-bone gap. The gap groups were subjected to a standard cyclic fatigue-loading protocol. The pullout strength of the pedicle screws for all specimens were then determined. RESULTS The pullout strength of the 1-mm and 2-mm groups were significantly reduced when compared with the intact group. A moderate to excellent positive correlation was identified between the cortical bone area ratio and pullout strength for all groups (r > 0.55). A cortical shell ratio of 0.73 or higher was also found to be a safe cut-off index for screw fixation failure, even with an observable 1-mm screw-bone gap. CONCLUSIONS The current in vitro cadaveric spine study identified a significant correlation between cortical bone area ratio and the thoracic pedicle screw pullout strength. The presented results also demonstrate that the fatigue-loading-induced screw-bone gap of 1-mm was sufficient to cause a significant decrease in the pullout strength. However, a cortical bone area ratio of 0.73 or higher in this group was able to preserve most of the screw-bone interfacial strength, and subsequently may prevent a complete implant failure.
Collapse
|