• Atlantoaxial dislocation
• Basilar invagination
• High-riding vertebral artery
• Pedicle screw
• Surgical techniques

• c1 laminectomy
• c1–2 fusion
• occipitocervical fusion
• retro-odontoid pseudotumor
• rheumatoid arthritis

• Humans
• Male
• Pedicle Screws
• Female
• Feasibility Studies
• Retrospective Studies
• Adult
• Middle Aged
• Cervical Vertebrae/surgery
• Cervical Vertebrae/diagnostic imaging
• Spinal Fusion/methods
• Spinal Fusion/instrumentation
• Aged
• Platybasia/surgery
• Platybasia/diagnostic imaging
• Young Adult
• Treatment Outcome
• Vertebral Artery/surgery
• Vertebral Artery/diagnostic imaging

• Alternative technique
• C1 posterior arch screw
• C2 laminar screw
• Odontoid fracture
• Supplemental technique
• Unilateral biplanar

• Humans
• Odontoid Process/surgery
• Odontoid Process/injuries
• Odontoid Process/diagnostic imaging
• Male
• Female
• Adult
• Middle Aged
• Spinal Fractures/surgery
• Spinal Fractures/diagnostic imaging
• Fracture Fixation, Internal/methods
• Bone Screws
• Atlanto-Axial Joint/surgery
• Atlanto-Axial Joint/diagnostic imaging
• Treatment Outcome
• Aged
• Young Adult

• Humans
• Cervical Vertebrae/surgery
• Bone Density
• Bone Screws
• Radiography
• Tomography, X-Ray Computed
• Biomechanical Phenomena
• Cadaver

• C2 pedicle screw
• C2 pediculoisthmic component
• Cervical spine
• High-riding vertebral artery
• Multiplanar reconstruction

• 3D-A2020006 the 3D-printing research project of Guangdong Second Provincial General Hospital

• atlantoaxial joint
• bone screws
• cervical vertebrae
• joint instability
• surgical fixation devices

• atlantoaxial fusion
• cervical spine
• mucopolysaccharidoses
• occipitocervical fusion
• surgical managements

• Alternate surgery techniques
• Cirugía de salvamento
• Complicaciones quirúrgicas
• Salvage surgery
• Surgical complications
• Traumatismo cervical superior
• Técnicas de cirugía alternativa
• Upper cervical trauma

• Male
• Female
• Humans
• Aged
• Retrospective Studies
• Spinal Fusion/methods
• Bone Screws
• Fracture Fixation, Internal/methods

• Anatomy
• Basilar invagination
• C2 pedicle
• Computed tomography
• Malformation
• Pedicle screws

• C2 medial window screw
• High-riding vertebral artery
• Narrow pedicle
• Pedicle screw
• Vertebral artery groove violation

• Atlanto-Axial Joint
• Biomechanical Phenomena
• Cervical Vertebrae/surgery
• Finite Element Analysis
• Humans
• Joint Instability
• Pedicle Screws
• Range of Motion, Articular
• Spinal Fusion
• Vertebral Artery/surgery

The use of translaminar screws may serve as a viable salvage method for complicated cases. To our understanding, the study of the feasibility of translaminar screw insertion in the actual entire subaxial cervical spine has not been carried out yet. The purpose of this study was to report the feasibility of translaminar screw insertion in the entire subaxial cervical spine.

Eighteen cadaveric spines were harvested from C3 to C7 and 1-mm computed tomography (CT) scans and three-dimensional reconstructions were created to exclude any bony anomaly. Thirty anatomically intact segments were collected (C3, 2; C4, 3; C5, 3; C6, 8; and C7, 14), and randomly arranged. Twenty-one segments were physically separated at each vertebral level (group S), while 9 segments were not separated from the vertebral column and left in situ (group N–S). CT measurement of lamina thickness was done for both group S and group N–S, and manual measurement of various length and angle was done for group S only. Using the trajectory proposed by the previous studies, translaminar screws were placed at each level. Screw diameter was the same or 0.5 mm larger than the proposed diameter based on CT measurement. Post-insertion CT was performed. Cortical breakage was checked either visually or by CT.

When 1° and 2° screws of the same size were used, medial cortex breakage was found 13% and 33% of the time, respectively. C7 was relatively safer than the other levels. With larger-sized screws, medial cortex breakage was found in 47% and 46% of 1° and 2° screws, respectively. There were no facet injuries due to the screws in group N–S.

Translaminar screw insertion in the subaxial cervical spine is feasible only when the lamina is thick enough to avoid any breakage that could lead to further complications. The authors do not recommend inserting translaminar screws in the subaxial cervical spine except in some salvage cases in the presence of a thick lamina.

Traumatic atlantoaxial rotatory subluxation after type 3 odontoid fracture is an uncommon presentation that may require complex intraoperative reduction maneuvers and presents challenges to successful instrumentation and fusion.

The authors report a case of a 39-year-old female patient who sustained a type 3 odontoid fracture. She was neurologically intact and managed in a rigid collar. Four months later, she presented again after a second trauma with acute torticollis and type 2 atlantoaxial subluxation, again neurologically intact. Serial cervical traction was placed with minimal radiographic reduction. Ultimately, she underwent intraoperative reduction, instrumentation, and fusion. Freehand C1 lateral mass reduction screws were placed, then C2 translaminar screws, and finally lateral mass screws at C3 and C4. The C2–4 instrumentation was used as bilateral rod anchors to reduce the C1 lateral mass reduction screws engaged onto the subluxated atlantodental complex. As a final step, cortical allograft spacers were inserted at C1–2 under compression to facilitate long-term stability and fusion.

This is the first description of a technique using extended tulip cervical reduction screws to correct traction-irreducible atlantoaxial subluxation. This case is a demonstration of using intraoperative tools available for the spine surgeon managing complex cervical injuries requiring intraoperative reduction that is resistant to traction reduction.

To assess the biomechanical effect of lateral inclination C₁ and C₂ pedicle screws on the atlantoaxial fixation through vitro human cadaveric study.

From January 2016 to December 2017, fresh‐frozen cadaveric cervical spines with intact ligaments from eight donated cadavers at an average age of 71.5 ± 10.6 years, comprising of six males and two females, were collected. There were no fracture and congenital malformation in all specimens according to the imaging examination. The range of motion (ROM) of the specimens were tested in their intact condition and destabilized condition. Next, the specimens were randomly divided into two groups to ensure no differences in sex and age: Group 1 was medial inclination C₁ pedicle screw and C₂ pedicle screws (C₁MPS‐C₂PS) and Group 2 was lateral inclination C₁ pedicle screw and C₂ pedicle screws (C₁LPS‐C₂PS). The ROM of the fixation scenarios were recorded. Thereafter, all the specimens with fixation constructs were tested for 1,000 cycles of axial rotation and tensile loading to failure was carried out collinearly to the longitudinal axis of all the screws, the data were documented as screw pullout strength (SPS) in newtons. All the recorded data subjected to quantitative analysis.

The ROM of specimens was increased significantly in destabilized condition and significantly reduced in fixation condition compared with intact condition. In C₁LPS‐C₂PS groups, the C₁‐C₂ cervical segment showed 3.96° ±1.21° and 3.75° ± 1.33° in flexion and extension direction, 2.85° ± 0.91° and 2.96° ± 0.71° in right and left lateral bending, 2.20° ± 0.43° and 2.15° ± 0.40° in right and left axial rotation. In C₁MPS‐C₂PS groups, it showed 4.24° ±1.31° and 3.98° ± 1.21° in flexion and extension direction, 2.76° ± 1.10° and 3.23° ± 0.62° in right and left lateral bending, 2.20° ± 0.46° and 2.21° ± 0.42° in right and left axial rotation. There was no statistically significant difference on ROM and screw pullout strengths (764.29 ± 129.00 N vs 714.55 ± 164.63 N) between the two groups. However, there was one specimen in the C₁MPS‐C₂PS group showing rupture the inferior wall of the left screw trajectory owing to the relatively thin posterior arch of the atlas, the screw pullout strength was significantly reduced (left pullout strength value: 430.5 N, right pullout strength value: 748.4 N). Therefore, in the case of the thin posterior arch of the atlas, the C₁LPS‐C₂PS group had strong long‐term biomechanics.

The lateral inclination C₁ pedicle screw can achieve the same biomechanical strength as the traditional atlas pedicle screw. However, for the case where the posterior arch of the atlas is relatively thin, a lateral inclination C₁ pedicle screw is more suitable.

• Atlantoaxial fixation
• Cadaveric study
• Lateral inclination C1 pedicle screw
• Lateral inclination C2 pedicle screw
• Narrow C1 posterior arch

• Atlantoaxial subluxation
• Axis
• Cervical fusion
• OC fusion
• Occipitocervical fusion
• Translaminar screw

• Biomechanics
• Occipital plate
• Occipitocervical fixation
• Pedicle screw
• Translaminar screw

• Biomechanical Phenomena/physiology
• Cadaver
• Cervical Vertebrae/diagnostic imaging
• Cervical Vertebrae/physiology
• Female
• Humans
• Imaging, Three-Dimensional/methods
• Internal Fixators
• Male
• Middle Aged
• Occipital Bone/diagnostic imaging
• Occipital Bone/physiology
• Pedicle Screws
• Range of Motion, Articular/physiology
• Weight-Bearing/physiology

• Atlantoaxial dislocation
• C1-C2
• High riding
• Pedicle screw
• Subfacetal
• Vertebral artery

To describe the clinical outcomes of occipitocervical fusion (OCF) using cervical pedicle fixation with assistance of O‐arm navigation and present its clinical feasibility.

From January 2015 to December 2016, eight patients with a variety of diagnoses were surgically treated with occipitocervical fusion using cervical pedicle screws under O‐arm navigation. All patients received full workup consisting of clinical and radiological assessments. Perioperative parameters including operating time, intraoperative blood loss, postoperative complications, surgical outcomes were recorded. Postoperative data were acquired resorting to the scheduled follow‐up 3, 6 and 12 months after their discharge and annually afterwards. The Japanese Orthopaedic Association (JOA) Scores and American Spinal Injury Association (ASIA) Scale were used to evaluate neurological function. The accuracy of screw placement was classified according to a modified classification of Gertzbein and Robbins. The fusion status was evaluated in reference to the Bridwell's posterior fusion grades.

The patient cohort comprised of five males and three females, with the average age of 51.9 years (range from 18 to 74 years). The patients all showed indications for OCF and were performed with polyaxial screws through cervical pedicles. The average operation time was 274 min (range from 226 to 380 min), with the intraoperative blood loss of 437.5 mL and the blood transfusion volume of 481.3 mL. The average follow‐up time was 23.5 months (range from 17 to 32 months). All patients exhibited radiographic evidence of osseous fusion by X‐ray and computed tomography (CT) at the final follow‐up. No neurovascular complications were found during the follow‐up time, and the clinical symptoms were observed to be significantly improved in all the patients. Thirty‐four cervical pedicle screws were implanted within the eight patients, with the accuracy of cervical pedicle screw placements as 94.1% (32/34), among which, two pedicle screws were found to broken through the cervical pedicles that were evaluated as Grade II.

Occipitocervical fusion via cervical pedicle fixation assisted with O‐arm navigation is a feasible and safe procedure with a vast range of indications.

• Cervical pedicle screw fixation
• O-arm navigation
• Occipitocervical fusion

• Case report
• Cervical spine
• International fixation
• Spinous process screw

The biomechanics of C1 posterior arch screw and C2 vertebral lamina screw techniques has not been well studied, and the biomechanical performance of the constructs cannot be explained only by cadaver testing.

From computed tomography images, a nonlinear intact three-dimensional C1-2 finite element model was developed and validated. And on this basis, models for the odontoid fractures and the three posterior internal fixation techniques were developed. The range of motion (ROM) and stress distribution of the implants were analyzed and compared under flexion, extension, lateral bending, and axial rotation.

All three kinds of fixation techniques completely restricted the range of motion (ROM) at the C1-2 operative level. The C1-2 pedicle screw fixation technique showed lower and stable stress peak on implants. The C1 posterior arch screw + C2 pedicle screw and C1 pedicle screw + C2 lamina screw fixation techniques showed higher stress peaks on implants in extension, lateral bending, and axial rotation.

As asymmetrical fixations, C1 posterior arch screw + C2 pedicle screw and C1 pedicle screw + C2 lamina screw fixations may offer better stability in lateral bending and axial rotation, but symmetrical fixation C1-2 pedicle screw can put the implants in a position of mechanical advantage.

• Atlantoaxial instability
• Biomechanics
• Finite element
• Range of motion
• Stress

• Atlantoaxial fusion
• Gallie technique
• Goel technique
• Harm’s technique
• Sonntag and Dickman technique
• brooks technique
• clamp
• lateral mass screw
• pedicle screw
• posterior cervical fusion
• screw fixation
• transarticular
• translaminar
• wires

Retrospective radiographic analysis.

Posterior fixation of C1 using screws is the most popular technique among the various methods for C1 stabilization, but it places the surrounding neurovascular structures at risk. Approximately 20% of the population has an anomalous groove for the vertebral artery; therefore, salvage methods are necessary. Therefore, we analyzed the feasibility of a newer C1 posterior arch crisscrossing screw fixation technique and studied its feasibility in the Indian population on the basis of the anatomy of the C1 posterior arch.

Multiple techniques have been described for C1–C2 fixation, such as wiring techniques, interlaminar clamps, transarticular screws, screw-plate/screw-rod system fixation, and hook-screw system fixation techniques, to provide rigid C1–C2 stability. However, although C1 fixation has evolved with time, it is not complication-free.

A 100 computed tomography (CT) scans of cervical spines with 1 mm slice thickness in the axial and sagittal sections obtained were randomly selected for the evaluation. Atlantoaxial anomalies due to trauma, deformities, infections, and tumors were excluded. All the images were measured for height of the posterior tubercle, width of the posterior arch, and length of the screw, and the screw projection angle was calculated. Demographic data were collected for all the subjects.

Out of the 88 CT scans analyzed, the mean height of the posterior tubercle was 7.4 mm, wherein 84.09% exceeded 7 mm, and the width of the posterior tubercle was 5.4 mm, wherein 88.6% (n=78) had posterior arch width >3.5 mm. A total of 13.6% (n=12) vertebrae were not suitable for screw placement, whereas 75% (n=66) vertebrae could accommodate 3.5×15 mm or longer screws. The screw projection angles ranged from 11.2° to 35° on the right and from 15.6° to 38.2° on the left.

C1 posterior arch screw fixation is a feasible and safe method because it poses little risk of injury to the surrounding neurovascular structures.

• C1 posterior arch
• Complications
• Crisscrossing
• Vertebral artery

Since C2 is adjacent to important nerves and blood vessels, the implantation risk of C2 internal fixation in this area is high and requires high accuracy. This study mainly discussed the application value of 3-dimensional (3D)-printed navigation template in C2 screw placement.

A retrospective study compared 3D-printed navigation template-assisted screw placement (group A, n=32) and the C-arm based navigation-assisted screw placement group (group B, n=32). Group A was divided into 2 subgroups: A1 (C2 pedicle screw placement) and A2 (C2 pars screw placement); group B was divided into B1 (C2 pedicle screw placement) and B2 (C2 pars screw placement). The accuracy and safety of screw placement and clinical outcomes were evaluated.

There were 64 C2 screws placed in group A, and 95.31% achieved a grade A accuracy rating, including 52 screws in group A1 (96.15% grade A) and 12 screws in group A2 (91.67% grade A). A total of 64 C2 screws were placed in group B, and 84.38% achieved a grade A accuracy rating, including 50 screws in group B1 (84.00% grade A) and 14 screws in group B2 (85.71% grade A). The accuracy of screw placement differed significantly between groups A and B (P=0.041) and between groups A1 and B1 (P=0.039) but not between groups A2 and B2 (P=0.636). The postoperative efficacy of the 2 groups was satisfactory. And there were no complications of blood vessels or nerves related to screw placement in either group.

Although 3D-printed navigation template-assisted and C-arm based navigation-assisted C2 pedicle and pars screw placement provided similar safety and clinical efficacy, 3D-printed navigation template technology achieved more accurate C2 pedicle screw placement.

• axial spine
• posterior fixation
• posterior fusion
• subaxial spine
• thoracic spine
• translaminar screw

• AA = atlantoaxial
• ADI = atlantodental interval
• HRVA = high-riding VA
• TAS = transarticular screw
• VA = vertebral artery
• atlantoaxial fixation
• cervical
• pars screw
• pedicle screw
• translaminar screw

• Adult
• Aged
• Atlanto-Axial Joint/surgery
• Axis, Cervical Vertebra/surgery
• Cervical Vertebrae/surgery
• Female
• Humans
• Joint Instability/surgery
• Male
• Middle Aged
• Postoperative Complications/etiology
• Postoperative Complications/surgery
• Range of Motion, Articular/physiology
• Retrospective Studies
• Spinal Fusion/methods
• Vertebral Artery/surgery

The Magerl and Goel-Harms techniques have been reported to produce excellent treatment outcomes in cases of atlantoaxial subluxation, but they also carry a risk of vertebral artery injuries. In order to completely prevent such injuries, we developed a surgical procedure, involving bone grafting between the C1 posterior arch and C2 lamina with clamp- or hook-and-rod-based fixation combined with the insertion of an interference screw into the posterior atlantoaxial joint.

This was a retrospective single-center study. The subjects were 58 patients in whom atlantoaxial subluxation was treated with the abovementioned procedure after 1995 (33 patients with rheumatoid arthritis (RA group) and 25 patients without rheumatoid arthritis (non-RA group)). The clinical outcomes and imaging findings of anterior subluxation at ≥ 2 years after surgery were compared between the RA and non-RA groups.

No vertebral artery injuries occurred during surgery. Seven and two patients died during the follow-up period in the RA and non-RA groups, respectively, but none of these deaths were associated with surgery. At ≥ 2 years after surgery, the visual analogue scale score, Japanese Orthopaedic Association score, and Ranawat classification had significantly improved in both groups (p < 0.001). Radiologically, bone fusion was noted in all patients. Significant changes in the atlas-dens interval (ADI) were seen immediately after surgery in both groups (p < 0.001). In the non-RA group, significant changes in the corrected atlantoaxial height were observed immediately after surgery (p < 0.01), and loss of correction was seen at the final follow-up, but it was not significant (p = 0.1965). No significant changes were noted in any other parameter. Regarding the postoperative alignment of the cervical spine, lordosis tended to decrease, but additional surgery was only performed in one patient, who had developmental stenosis at the mid-lower level and belonged to the RA group. No reoperations due to fused adjacent segmental disease or exacerbated curvature were required.

In the present study, no vertebral artery injuries occurred during surgery, and no major perioperative complications developed. Favorable clinical outcomes were observed at ≥ 2 postoperative years although the patients’ diseases varied. This procedure produced superior outcomes, especially in terms of spinal correction and the maintenance of the ADI.

• Atlantoaxial subluxation
• Hook-rod constructs
• Interference screw
• Vertebral artery injury

• Allograft
• Autograft
• Bone morphogenetic protein (BMP)
• C1-C2
• Iliac crest graft
• Nonunion
• Polyaxial screws

• Clival chordoma
• Instability
• Occipito-cervical fusion
• Occipito-cervical joint

• Biomechanics
• Craniospinal junction
• Offset connector
• Pedicle screw
• Translaminar screws

• Atlantoaxial
• Bicortical
• Biomechanical testing
• Pedicle screws
• Translaminar screws
• Unicortical.

• Anatomic measurements
• Axis
• Bifid base
• Biomechanical
• C2
• Cervical fixation
• Cortical bone trajectory
• Pullout
• Screw trajectory
• Spinous process

• Atlantoaxial fixation
• Atlantoaxial instability
• Biomechanics
• C1 posterior arch screw
• Laminar screw
• Unilateral

• Anatomical trajectory pedicle screws
• Biomechanics
• Cervicothoracic junction
• Insertion torque
• Laminar screw
• Lateral mass screw
• Pedicle screw
• Pull-out strength

Translaminar screw fixation (TSF) of the axis is considered as an efficient, safe and simple surgical procedure, however the study of the potential risk of TSF to the transverse foramen in lower cervical spine is lacked. Head-neck CT images of 60 patients were included in this study. Maximum screw length, laminar thickness, the screw angle and the laminar height were measured. The feasibility of 3.5-mm diameter screw fixation and the potential risk of transverse foramen injury was analyzed. The TSF was safe at C3 and C4, but risky to the transverse foraman at a rate of 8.7% at C5 (0% on the left side and 20% on the right side), 33.3% at C6 (24.4% on the left side and 42.9% on the right side). C7 had the highest 77.8% rate (65.5% on the left side and 89.8% on the right side). The safe screw length was 27.7 mm at C3, 27.4 mm at C4, 28.0 mm at C5, 25.6 mm at C6 and 25.5 mm at C7, respectively. The present study showed that translaminar screw could place the transverse foramen of C5–C7 at risk. Preoperative CT scanning was necessary for safe screw placement.

The C2 pedicle screw is more biomechanically stable and provides patients with increased postoperative range of motion in comparison to other methods of C2 fixation. However, as a result of the proximity of the C2 pedicle to the transverse foramen, there is a considerable risk of intraoperative morbidity due to vertebral artery injury laterally or vertebral canal breach medially. Other than the use of cadavers for the demonstration and practice of C2 pedicle screw placement, there are currently few other readily available teaching aids for the training of residents and fellows. Herein, we describe a simple and cost effective modality for the demonstration, evaluation, and practice of C2 pedicle screw placement in a laboratory setting.

• c2 pedicle screw
• teaching aid
• technique

• Biomechanical testing
• Biomechanics
• C2 pedicular screw
• Cadaveric study
• Isthmic screw

Multiple techniques exist for the fixation of C2, including axial pedicle screws and bilateral translaminar screws. We describe a novel method of incorporating both the translaminar and pedicle screws within C2 to improve fixation to the subaxial spine in patients requiring posterior cervical instrumentation for deformity correction or instability. We report three cases of patients with cervical spinal instability, who underwent cervical spine instrumentation for stabilization and/or deformity correction. Bilateral C2 pedicle screws were inserted, followed by bilateral crossed laminar screws. The instrumentation method successfully achieved fixation in all three patients. There were no immediate postoperative complications, and hardware positioning was satisfactory. Instrumenting C2 with translaminar and pedicle screws is technically feasible, and it may improve fixation to the subaxial spine in patients with poor bone quality or severe subaxial deformity, which require a stronger instrumentation construct.

• Axis fixation
• C2 pedicle screws
• C2 translaminar screws
• Subaxial fixation

• Atlantoaxial instability
• Clamp
• Lateral mass screw
• Pedicle screw
• Posterior fixation
• Screw fixation
• Wires