Effectiveness of the induced membrane technique in aseptic and infected long-bone defect management: Are there any differences?

Abstract

Management of post-traumatic long-bone defects remains relevant and challenging despite the rapid development of approaches to their treatment. Dominant positions are occupied by the Ilizarov method, bone autogenous grafting and the Masquelet induced membrane technique (IMT). The IMT is aimed at reducing extensive defect treatment duration and for this reason has gained great popularity. However, the assessment of its effectiveness is difficult due to a limited number of clinical series. The varying clinical manifestations of bone defect severity do not allow a comprehensive evaluation of IMT effectiveness. One of them is infection in the defect area. The purpose of our literature review is an analysis of studies on IMT application in infected vs non-infected long-bone defects of the lower extremities published over the last 10 years. It focuses on the investigation of similarities and fundamental differences in the need for antibiotics, timing of spacer fixation, methods of collecting donor bone and fixators used for consolidation. The studies show that the IMT has been globally used in aseptic and osteomyelitic defects due to its clinical effectiveness. Authors’ variations and improvements in its practical implementation indicate the ongoing development and the interest of researchers in this technique.

Key Words: Long bone; Nonunion; Defect; Induced membrane technique; Infection; Spacer; Intramedullary nail; External fixator; Osteomyelitis

Core Tip: The induced membrane (IM) technique (IMT) has been mostly used for severe long bone defects due to open fractures and infected nonunion. The clinical studies available show its performance and outcomes on relatively small samples of patients and they are mostly infected cases. The surgeon should adequately resect non-vital tissues to prevent bone auto- or allograft lysis due to possible reinfection. The IMT gives a chance for the infection to heal after thorough debridement within the waiting period during stage 1. Its implementation frequently needs soft-tissue procedures and several grafting materials to add into the IM in critical size defects. Internal fixation is a preferred method of bone fixation to avoid the risks of external fixation complications. The interval between the stages and duration of antibiotics administration are longer in infected cases.

INTRODUCTION

Severe long-bone fractures of the lower extremities are still a significant challenge for surgeons as up to 10% of such fractures develop bone healing disorders due to high-energy mechanisms of injury and fracture-related infection, especially if critical-size bone defects (CBDs) and nonunion develop after open injuries[1]. The incidence of infection following bone fractures varies from 2% in low-grade open fractures to 50% in the most severe injuries[2]. Bone defects differ in their etiology, location, size, presence of infection, and soft-tissue conditions[3]. The management of segmental long-bone defects due to severe open fractures, nonunion and bone infection is associated with prolonged treatment and compromised outcomes[4]. Post-traumatic osteomyelitis is a relatively common occurrence in segmental bone defects[3,5].

A classification system and treatment algorithm developed for management of post-traumatic bone defects considers several strategies to address bone and soft tissue components of segmental bone defects[4,6]. Dominant positions in this classification are occupied by the Ilizarov method, bone autogenous grafting and the Masquelet induced membrane (IM) technique (IMT)[4,6]. However, extensive segmental defects of long bones due to removal of all infected tissues and associated with severe osteomyelitis are extremely difficult to compensate with traditional reconstruction methods, such as the Ilizarov bone transport (IBT) and autologus grafting with vascularized fibula[2]. These treatment methods require high technical training and cannot be performed without special instrumentation[1,7-9].

The IMT has gained global popularity for managing aseptic and infected bone defects of various locations and of any type and shape (partial or complete, metaphyseal or diaphyseal) due to its clinical accessibility and effectiveness[7-10]. The original IMT has been used since 1986 and was developed initially by the author for treating long-bone defects due to bone infection[8,9]. It is based on the use of biological tissues, the IM and autologous bone grafting, for promoting regeneration and bone consolidation[10]. It is a two-stage bone reconstruction procedure that includes (1) debridement and insertion of a polymethyl metacrylate (PMMA) cement spacer into the bone defect for 4 to 8 week; and (2) autogenous grafting from the iliac crest or medullary canal of the femur and may be supported by demineralized bone. It is aided by either internal or external fixation. The process takes months to complete bone remodeling[8,9]. Full weight-bearing is authorized at 5 to 6 months after stage 2. However, unlike the IBT, it provides a better quality of life, especially if bone defects are located in the femur[7,9].

The IMT is aimed at reducing treatment duration of extensive and compromised bone defects in the lower extremity. Recent literature search has revealed that a great number of studies report on its outcomes and modifications[3-5]. However, the evaluation of its effectiveness in long-bone lower limb defect treatment is difficult due to varying clinical manifestations of bone defect severity and small clinical series that may include both infected and non-infected cases in different body segments.

The purpose of our literature review is an analysis of studies on IMT application in infected vs non-infected long-bone defects of the lower extremities published over the last 10 years focused on similarities and fundamental differences in the need for antibiotics, timing of spacer fixation, methods of collecting donor bone and fixators used for consolidation.

LITERATURE SELECTION

A scientometric comprehensive review of the literature published from 2004 to 2023 in the field of the Masquelet technique was presented in 2024 and identified a total of 1019 related studies, including reviews, systemic analyses, clinical and experimental studies[11]. The annual number of publications on IMT application has been growing rapidly since 2017. It is an enormous collection that is very difficult to examine.

We performed a comprehensive search in the available Internet platforms that index medical studies to identify only recent clinical studies on the treatment of lower limb long-bone defects with the IMT using the terms “induced membrane technique”, “Masquelet technique”, “long-bone defect”, “lower extremity”, “infected bone defect”. Clinical full-text studies in English with patient samples greater than 8 patients were chosen. Next, the studies were screened and those that reported on infected and non-infected bone defect management with the ITM were selected. They had to report on at least three treatment topics: Antibiotics usage and regime, timing and type of fixation, methods of collecting grafting material, rate of consolidation, complications including infection recurrence. Case series with fewer than 8 patients and reports on defects after tumor resection were excluded. Animal experimental studies and literature in languages other than English were not included either. All types of reviews were used only for narrative purposes. Manually, after extraction of full-text articles 24 clinical studies that comply with the selection criteria were analyzed for similarities and differences in the management of aseptic[12-19] and infected[20-34] lower limb long-bone defects with the IMT application.

MAIN DISCUSSION POINTS

Indications for IMT application

The reported studies show that IMT is suitable for treatment of a wide range of clinical conditions, primarily in the lower extremity cases with satisfying results[4,7,9,14]. The main conditions for which the IMT is used in the lower extremity are segmental bone defects, including CBDs due to open fractures, aseptic and infected nonunion, osteomyelitic defects of the femur and tibia.

IMT is used for the reconstruction of the tibia in two thirds of the cases of its total application[35,36]. The concept of applying IMT in acute cases has gained popularity in recent years[15-19,35]. The tibial diaphysis is marked as the site that represents numerous post-injury problems including inadequate soft-tissue coverage, limited blood supply, high weight-bearing function, and risk of deformities[34,37] and the site to which the IMT is mostly applied in both aseptic and septic conditions.

IMT stage 1

IMT stage 1 is similar for both aseptic and septic cases and consists of three phases[3,8,10]: (1) Radical debridement; (2) Fixation; and (3) Installation of a PMMA spacer impregnated or not with antibiotics.

DEBRIDEMENT

Aseptic defects

Thorough debridement and removal of nonunion end-plates and dead tissue in open fractures is obligatory to avoid infection. A special feature of atrophic nonunion debridement is equalization of the limb length, which is an important aspect of further rehabilitation[4,12]. It is also worth noting that extensive resection of end-plates and periosteal dissection disrupt the nutrition of the fragment ends and should be avoided.

Septic defects

Radical debridement involves removing all infected and non-viable bone and soft tissues, revising leaks and phlegmons, and removing foreign bodies involved in the process. The boundaries of viable and non-viable tissues are determined intraoperatively with the "paprika sign" or "bloody dew". To obtain more reliable results for determining the pathogen and sensitivity to antibiotics, a minimum of 3-5 deep tissue biopsies are performed[3,20]. Repeated debridement may be performed several times at stage 1 until infection suppression in the cases of resistant bacteria. In infected CBDs, repeated debridement and cement spacer replacement may be conducted weekly until infection resolution[37]. Recurrence of infection after IMT step 1 is always due to insufficient resection[9].

Debridement (Table 1) is a primary issue and should be repeated if bacterial cultures are detected at the end of stage 1 at spacer removal[9].

Table 1 Main differences in induced membrane technique application in aseptic and infected bone nonunion and defects.

	Debridement	Fixation options	Spacer characteristics	Antibiotics administration at stage 1	Interval between stage 1 and stage 2	Consolidation rates	Infection
Aseptic defects	Thorough debridement and removal of nonunion end-plates and dead tissue in open fractures is obligatory to avoid infection. A special feature of atrophic nonunion debridement is equalization of the limb length, which is an important aspect of further rehabilitation[4,12]. It is also worth noting that extensive resection of end-plates and periosteal dissection disrupt the nutrition of the fragment ends and should be avoided	The variability of fixation methods is extremely wide depending on the segment and location. Only internal fixation has been recommended recently for nonunion. A combination of intramedullary nailing and plating is widely used[12-14]. Internal fixation at IMT stage 1 not only prevents the development of infection in pin-tracts as happens in external fixation in the postoperative period, but also reduces the invasiveness of stage 2 as an IMN remains in situ. IMN is seen as the preferred method of fixation for tibial and femoral defects whenever possible[35]	Installation of a cement spacer impregnated with antibacterial drugs is not mandatory if culture tests do not detect resistant strains of bacteria. Despite the available experimental data that antibiotics reduce the membrane potential[39], antibacterial drugs were used in most clinical trials, as orthopedic surgeons regard their use to be safe as they fear low toxic infection	Empirical antibiotic therapy or antibiotic impregnated spacer may be used after debridement in acute cases[18]	Definitive control of infection is a prerequisite for continuing with graft reconstruction. Stage 2 starts after 4-8 weeks[4,10]. Confirmation of infection control is laboratory markers of inflammation, microbiological tests to detect the pathogen (tissue samples at the site of the segmental defect). Most authors are inclined to the minimum period of spacer placement (4-6 weeks) for aseptic pseudoarthrosis. Longer intervals may be determined exclusively by problems in the administration of treatment stages and infection[15]	Despite the relatively small number of patients in the reported series, high union rates from 88.2% to 92.7% were achieved. In the comparative series, there was no reliable difference with the series of one-stage bone grafting repair[14]. In acute defects, the success rate was 89 %[15]	Superficial infection was reported[12]. There were no reports of deep infection developed in aseptic nonunion. It indicates the high safety of the technique if it is performed correctly. Deep infection developed in acute cases[16]
Septic defects	Radical debridement involves removing all infected and non-viable bone and soft tissues, revising leaks and phlegmons, and removing foreign bodies involved in the process. The boundaries of viable and non-viable tissues are determined intraoperatively with the "paprika sign" or "bloody dew". To obtain more reliable results for determining the pathogen and sensitivity to antibiotics, a minimum of 3-5 deep tissue biopsies are performed[3,20]. Repeated debridement may be performed several times at stage 1 until infection suppression in the cases of resistant bacteria. In infected CBDs, repeated debridement and cement spacer replacement may be conducted weekly until infection resolution[37]. Recurrence of infection after IMT step 1 is always due to insufficient resection[9]	Regarding primary stabilization, a large majority of patients wore an external fixator until end of treatment in the IMT series of mostly infected cases presented by its author who considered that immediate nailing incurs a risk of recurrence of sepsis[9]. Temporary external fixators are recommended in the case of chronic infection[9]. Internal fixation is more preferred nowadays, and may be immediate, especially in the femur[35]. Plating may be combined with intramedullary nailing[21]. LCP was used as an external fixator with subsequent conversion to LCP and IMN at stage 2[22]	Installation of a cement spacer impregnated with antibacterial drugs is an overall practice. The preferred ratio is 4 g of vancomycin per 40 g of cement during spacer preparation[27]. Bone cement containing gentamicin can be used with the addition of 5 g vancomycin per 40 g gentamicin-impregnated PMMA bone cement[24-26]	Initially, empirical antibiotic therapy is initiated. It largely depends on national or local protocols, local antibiograms, patient’s history, and severity of local and systemic manifestations. Once the results of intraoperative bacterial cultures are available, the principle of systemic antibiotic therapy for osteomyelitis includes pathogen-directed therapy based on susceptibility, using drugs that achieve the required concentration in bone tissue. Antibiotic therapy should be continued for at least 4-6 weeks; shorter periods may be acceptable only in children. Immunosuppression, including that caused by diabetes and human immunodeficiency virus infection, may require longer treatment for 6-12 weeks. Long-term (more than 3 months) oral antibiotic therapy at the outpatient stage may improve outcomes[42]. A severe infection variant is the aforementioned hospital-acquired infection. MRSA is associated with higher rates of recurrence[20]	Complete suppression of infection is a prerequisite for bone defect grafting in osteomyelitis. Sending tissue samples for examination is extremely important due to possible false-negative results of bacteriological culture. Stage 2 starts after 8 to 12 weeks[3,21,24,32] or longer up to 28-32 weeks due to local status[27,29,31]. In most severe cases, removal of infected tissues frequently results in extensive bone loss in the diaphysis. The resistant strains recur frequently and thus stage 1 may be longer than in aseptic cases[37] due to redebridement	Radiographic signs of consolidation were achieved on average within 5 to 9 months, with a range of 4 to 16 months; consolidation was achieved in 69%-100% of cases[20-29,47]	Although several clinical studies have yielded favorable results, high rates of infection and mixed results were reported[20,46-48]. There are few large homogenous series using a standardized IMT protocol for the treatment of infected nonunion and posttraumatic osteomyelitis. The evidence in treating challenging infections shows the rates of reinfection within 40% after bone grafting[20]. Reinfection of 68.5% was reported isolating Staphylococcus (26%) and more than one pathogen (22%)[46]

IMT: Induced membrane technique; IMN: Intramedullary nailing; CBD: Critical-size bone defect; LCP: Compression plate; PMMA: Polymethyl metacrylate; MRSA: Methicillin-resistant Staphylococcus aureus.

Similar fixation options are available for both conditions. After debridement and removal of dead tissues, stabilization is performed using external fixation options, plates or intramedullary nails. These fixation options can be either temporary or left at stage 2. The length of the plate depends on whether at least 2 or 3 screws can be used in each bone fragment for fixation, and 2 to 4 screws are needed in the bone defect area to connect the cement and the plate[21]. It was proposed to cross over from external to internal fixation at stage 2[9]. One of the largest studies concluded that intramedullary nailing (IMN) is more preferable for critical size defects in the femur and tibia[38]. The results showed that patients treated with it had faster union, fewer grafting procedures, and fewer reoperations than those treated with plates, especially in the femur due to earlier weight-bearing in IMN application. The advantage of IMN over plating is that weight-bearing can be resumed before radiological confirmation of consolidation[9].

The specific different fixation approaches exist (Table 1).

FIXATION OPTIONS

Aseptic defects

The variability of fixation methods is extremely wide depending on the segment and location. Only internal fixation has been recommended recently for nonunion. A combination of IMN and plating is widely used[12-14]. Internal fixation at IMT stage 1 not only prevents the development of infection in pin-tracts as happens in external fixation in the postoperative period, but also reduces the invasiveness of stage 2 as an IMN remains in situ. IMN is seen as the preferred method of fixation for tibial and femoral defects whenever possible[35].

Septic defects

Regarding primary stabilization, a large majority of patients wore an external fixator until end of treatment in the IMT series of mostly infected cases presented by its author who considered that immediate nailing incurs a risk of recurrence of sepsis[9]. Temporary external fixators are recommended in the case of chronic infection[9]. Internal fixation is more preferred nowadays, and may be immediate, especially in the femur[35]. Plating may be combined with IMN[21]. Compression plate (LCP) was used as an external fixator with subsequent conversion to LCP and IMN at stage 2[22].

The next similar step after limb stabilization is the installation of a PMMA spacer (Table 1) to fill the segmental bone defect for local delivery of antibiotics, to prevent fibrous tissue proliferation, to replenish the volume of dead space until reconstruction, and to induce the formation of a biologically active membrane[3,21].

At the end of the first stage, it is necessary to close the wound without tension. This may require various methods of closing the wound surface with different types of flaps in open fractures[9,11,23-27]. The infection process due to injury or multiple surgical interventions is often accompanied by soft-tissue defects; therefore various soft-tissue plastic options are required. In selected patients with tibial osteomyelitis combined with soft-tissue defects, the anterolateral femoral free flap and the Masquelet technique was an effective treatment strategy. It yielded effective limb restoration after trauma, suppression of infection, and improvement of flexion and extension in the knee and ankle joints[34].

The IMT author used a cement spacer without antibiotics even in infected cases stating that antibiotic-loaded cement could mask insufficient debridement and resection of bone and/or soft tissues[9]. It was supposed that the antibiotics in the cement affect the physical properties of the membrane, but the authors did not specify whether this impaired osteogenesis[39,40]. The higher the antibiotic concentration is, the more fragile is the cement. In turn, this simplifies spacer removal at stage 2 and spares the IM. There is evidence that vancomycin is used as an antibiotic of choice because it is sensitive to most pathogenic bacteria. It is a reserve antibiotic for the most common pathogen, Staphylococcus aureus(S. aureus), including methicillin-resistant S. aureus (MRSA)[2]. Its prolonged action is superior to other antibiotics, and its concentration when applied locally is approximately 200 times higher than when administered intravenously. Local delivery of the antibiotic increases its concentration at the bone defect site several times higher than the minimum inhibitory concentration and without its growth in the blood, which significantly reduces systemic side effects. It has been shown that the average doses of 10.5 g vancomycin and 12.5 g gentamicin in antibiotic-impregnated cement were clinically safe in the long term without any evidence of systemic side effects, including acute renal failure. However, it is still preferable to add 4.0 g of vancomycin per 40.0 g of cement[27].

SPACER CHARACTERISTICS

Aseptic defects

Installation of a cement spacer impregnated with antibacterial drugs is not mandatory if culture tests do not detect resistant strains of bacteria. Despite the available experimental data that antibiotics reduce the membrane potential[39], antibacterial drugs were used in most clinical trials, as orthopedic surgeons regard their use to be safe as they fear low toxic infection.

Septic defects

Installation of a cement spacer impregnated with antibacterial drugs is an overall practice. The preferred ratio is 4 g of vancomycin per 40 g of cement during spacer preparation[27]. Bone cement containing gentamicin can be used with the addition of 5 g vancomycin per 40 g gentamicin-impregnated PMMA bone cement[24-26].

In acute open fractures without significant environmental contamination, infection is caused by skin flora, mainly S. aureus and coagulase-negative staphylococci. However, in open fractures with severe environmental contamination, gram-negative microorganisms such as Pseudomonas aeruginosa (P. aeruginosa), Enterobacter cloacae (E. cloacae) and Escherichia coli (E. coli), other gram-positive ones such as Bacillus and Enterococcus spp., and even anaerobes may penetrate in the wound[2]. Moreover, patients with open fractures due to high-energy trauma with extensive soft-tissue damage are at increased risk of nosocomial infection with pronounced drug resistance. The results of microbiological tests taken directly during primary surgical intervention are often ineffective for etiotropic therapy.

Gram-positive microflora dominates in osteomyelitic infection (coagulase-negative staphylococcus, methicillin-sensitive staphylococcus, methicillin-resistant staphylococcus). Gram-negative pathogens (E. coli, P. aeruginosa, E. cloacae) are less frequent. Detection of Klebsiella pneumoniae and the genus Acinetobacter grows[1,24]. Associations of microorganisms aggravate the course of the disease, and may amount from 22.9% to 36.6%. In chronic osteomyelitis, microbiological tests of the material from the infection site most often detect two-component associations of bacteria: P. aeruginosa + S. aureus; E. cloacae + S. aureus, S. aureus + Coagulase-negative Staphylococci. The dominant microorganisms in mixed cultures are strains of S. aureus and P. aeruginosa. The osteomyelitic course is complicated by the fact that some strains in the biofilm can produce ß-lactamases, which leads to protection of other pathogens[41].

ANTIBIOTICS ADMINISTRATION AT STAGE 1

Aseptic defects

Empirical antibiotic therapy or antibiotic impregnated spacer may be used after debridement in acute cases[18].

Septic defects

Initially, empirical antibiotic therapy is initiated. It largely depends on national or local protocols, local antibiograms, patient’s history, and severity of local and systemic manifestations. Once the results of intraoperative bacterial cultures are available, the principle of systemic antibiotic therapy for osteomyelitis includes pathogen-directed therapy based on susceptibility, using drugs that achieve the required concentration in bone tissue. Antibiotic therapy should be continued for at least 4-6 weeks; shorter periods may be acceptable only in children. Immunosuppression, including that caused by diabetes and human immunodeficiency virus infection, may require longer treatment for 6-12 weeks. Long-term (more than 3 months) oral antibiotic therapy at the outpatient stage may improve outcomes[42].

A severe infection variant is the aforementioned hospital-acquired infection. MRSA is associated with higher rates of recurrence[20].

There is still no unambiguous and globally accepted principle in the approach to prescribing antibiotic therapy after debridement in osteomyelitic cases. The initial therapy has not been determined and it is not clear whether it is necessary to consider the results of culture tests from the fistula tract. Or there should be an initial therapy with broad-spectrum antibiotics and its subsequent adjustment after culture tests from 3-5 sites. It is reasonable to rely on microbiological studies of cultures from fistula tracts, wounds or the purulent focus area performed the day before the puncture, with subsequent adjustment based on the study of surgical tissues. It is obvious that it is necessary to start with intravenous administration for 2 weeks after debridement, followed by transition to oral antibiotics for up to 4 weeks. However, most studies of infected defects focus primarily on surgical tactics and do not report a complete protocol of systemic antibiotics after debridement and redebridement[22-27,29-32]. Antibiotic protocols for infected defects prescribe a longer administration of antibiotics according to culture tests (Table 1). A protocol may include at least 2 weeks of an antibiotic drug holiday prior to the initial debridement and targeted intravenous antibiotics that are administered after it under the guidance of an infectious disease specialist for at least 6 weeks[20]. It was advised that if the culture was positive after a negative post-debridement results from the previous stage in multi-stage debridement, adjuvant targeted generation IV antibiotics were administered for at least 4 or 6 weeks from the time of the last positive culture[20]. Multiple steps to address recalcitrant recurrent infections included thorough debridement and antibiotic-loaded cement spacer (vancomycin 4 g +, tobramycin 0.4 g per 40 g PMMA) at stage 1 and temporary stabilization using an external fixator, temporary plating, an antibiotic-loaded cement rod, or a combination of them. The second step was secondary debridement and conversion to the definitive fixation and an antibiotic-loaded PMMA cement spacer. The final stage involved removing the cement spacer and bone grafting once the infection was eradicated.

INTERVAL BETWEEN STAGE 1 AND STAGE 2

Aseptic defects

Definitive control of infection is a prerequisite for continuing with graft reconstruction. Stage 2 starts after 4-8 weeks[4,10]. Confirmation of infection control is laboratory markers of inflammation, microbiological tests to detect the pathogen (tissue samples at the site of the segmental defect). Most authors are inclined to the minimum period of spacer placement (4-6 weeks) for aseptic pseudoarthrosis. Longer intervals may be determined exclusively by problems in the administration of treatment stages and infection[15].

Septic defects

Complete suppression of infection is a prerequisite for bone defect grafting in osteomyelitis. Sending tissue samples for examination is extremely important due to possible false-negative results of bacteriological culture. Stage 2 starts after 8 to 12 weeks[3,21,24,32] or longer up to 28-32 weeks due to local status[27,29,31]. In most severe cases, removal of infected tissues frequently results in extensive bone loss in the diaphysis. The resistant strains recur frequently and thus stage 1 may be longer than in aseptic cases[37] due to redebridement.

The IM becomes biologically active after 2 to 4 weeks. At this time-point, the levels of biologically active substances [vascular endothelial growth factor, transforming growth factor beta, and bone morphogenetic protein (BMP)] reach their peak level and then decrease after 6 to 8 weeks[3]. As advised by the IMT author, the optimal time to start the second stage is between 4 and 8 weeks (Table 1) once the infection is not detected. However, in his historic series the intervals between the two operative steps were longer due to wound care and soft-tissue healing time[9]. Another reason for a longer interval is several debridement steps due to occurrence of infection or reinfection in infected defects[20,28]. Multiple tissue biopsy specimens must be sent for microbiological analysis during both stages of the IMT procedure and at least five intraoperative tissue samples are taken.

IMT stage 2

The second stage should be performed only after repeated tests for leukocytes, C-reactive protein and erythrocyte sedimentation rate counts and after the wound healed well without local signs of infection[27].

Materials for grafting at stage 2 are harvested from similar sources (Table 1). The resulting bone defect is best filled with crushed autogenous bone graft. Bone graft material utilized is autologous cancellous pieces or filtered reamer-irrigator-aspirator (RIA) graft. It can be expanded further with osteoconductive, osteoinductive, and osteogenic material[9]. The synergistic regenerative effect is achieved by the bone graft and the IM. It promotes active osteoinduction, neoangiogenesis, bone defect healing and consolidation due to stimulation of the release of growth factors such as VEGF, TGF-beta 1 and BMP-2[3].

Bone grafting material can be obtained from several sites, including the iliac crest, proximal tibia and the calcaneus. The RIA graft from the femur allows obtaining large volumes for grafting. Thereby, pain in the donor area is lower than with harvesting the traditional iliac crest bone graft. However, the RIA is associated with a number of technical complications such as eccentric reaming of the medullary canal, cortical perforation, femoral fractures, and heterotopic ossification. Also, significant blood loss is a formidable complication requiring blood transfusion and correction of anemia. In that case, the talk about stimulation of local osteogenesis sounds inappropriate[43].

Autografts contain osteoblast precursor cells (mesenchymal stem cells) and tissue growth factors (BMP-2, FGF-2, IGF-1, and TGF-β) that accelerate bone regeneration[3]. The bone graft should be loosely packed to fill the bone defect. It is important to avoid dense packing of the bone graft when filling the defect, as this may lead to graft necrosis due to impaired angiogenesis. Large defects may require additional augmentation of the autogenous bone graft with allograft or demineralized bone graft in a ratio of no more than 1:3 (autograft to allograft) to achieve sufficient graft volume or strength[9]. Autogenous bone graft may also be supplemented with synthetic BMP, bisphosphonates, or hydroxyapatite. Masquelet et al[44] recommend at least 70% volume of autografts while using additional graft substitutes. The allograft portion exceeded 30% of graft volume in four cases in the study of established infected and noninfected pseudarthrosis and acute bone loss[35]. Of the three failed cases in that series, two were treated with less than 70% of autogenous bone grafts. The insufficient iliac bone source after multiple previous interventions should be considered before the application of IMT, particularly in bone defects exceeding 6 cm[35]. Although there are studies that showed that a high proportion of allograft (up to 64%) enabled to achieve the same rates of graft healing as the series in which the proportion of allograft was lower[31]. Critical size defects (62 mm) need special attention and would require IMT modifications or several grafting procedures though the author of the method opined differently[36,44]. Amount of graft material does depend on the presence of infection. Infected bone defects in the lower limb would need more graft material as the debridement is more extensive in septic cases. Thus, vancomycin-augmented allografts were used for large defects[36]. Multi-perforated non-vascularised fibular graft with multiple 2-mm drill holes along the entire surface was applied to fill large defects (mean, 14 cm) to reconstruct massive post-traumatic defects in military practice[45].

CONSOLIDATION RATES

Aseptic defects

Despite the relatively small number of patients in the reported series, high union rates from 88.2% to 92.7% were achieved. In the comparative series, there was no reliable difference with the series of one-stage bone grafting repair[14]. In acute defects, the success rate was 89%[15].

Septic defects

Radiographic signs of consolidation were achieved on average within 5 to 9 months, with a range of 4 to 16 months; consolidation was achieved in 69%-100% of cases[20-29,46].

Bone healing of the defect is independent of its size as postulated by the IMT author[44]. It depends, first of all, on the conditions created in the biologically active environment of the defect. Stable fixation of bone fragments is fundamental. Without mechanical stability along with the correct position of the fragments, healing of hypertrophic nonunion is almost impossible. It is stable retention of bone fragment ends, correct segment axis and maximum equalization of the limb length that switch on tissue mechanisms (vascularization of the defect zone, osteoconductive matrix), cell (osteogenic cells) and molecular levels (growth factors) aimed at restoring the integrity and continuity of the bone.

However, the opposite pattern was revealed for acute defects: The effectiveness of IMT in acute bone loss primarily depends on the size of bone defect, and not on the damaged area and soft tissue defects[15]. It is concluded that the defect size of about 6 cm is favorable for IMT implementation. Another recent study found that there was a significant correlation between defect length and time to reach full weight-bearing[36]. Eighty-nine percent of the patients reported by that study achieved full weight-bearing at the end of the therapy. The average time from initiation of therapy to reaching safe full weight-bearing was 589 days for an average defect size of 58 mm (+/- 31 mm).

Multi-staged IMT protocol based on post-debridement culture in treating patients with critical-sized bone defect in the lower extremity of 140 patients due to infected nonunion or post-traumatic osteomyelitis was utilized to evaluate the success rate of this limb reconstruction method and risk factors associated with recurrence of infection[20]. They were followed up for more than 24 months after bone grafting. The primary success rate of limb reconstruction was 75% with a mean follow-up of 45.3 months. However, another study showed that the average period of bone tissue remodeling was 16.33 months, with consolidation achieved in 50% of cases[30]. In another cohort study, the IMT for acute bone loss was abandoned for several reasons (nonunion and infection among them) and was replaced with distraction osteogenesis[16].

Complications

The main concern is occurrence or recurrence of infection (Table 1) that requires debridement of the membrane and surrounding soft tissues and reinitiation of the technique[9,44].

INFECTION

Aseptic defects

Superficial infection was reported[12]. There were no reports of deep infection developed in aseptic nonunion. It indicates the high safety of the technique if it is performed correctly. Deep infection developed in acute cases[16].

Septic defects

Although several clinical studies have yielded favorable results, high rates of infection and mixed results were reported[20,46-48]. There are few large homogenous series using a standardized IMT protocol for the treatment of infected nonunion and post-traumatic osteomyelitis. The evidence in treating challenging infections shows the rates of reinfection within 40% after bone grafting[20]. Reinfection of 68.5% was reported isolating Staphylococcus (26%) and more than one pathogen (22%)[46].

Recurrence of infection in 9.5% to 13.1% of cases was observed after the second stage in septic nonunion treated with IMT[1,21,25,31]. The multi-staged IMT protocol based on post-debridement cultures in fracture-related infection revealed a number of risk factors for infection recurrence[20]. Independent risk factors for recurrence of infection were infected free flap, surprise positive culture, deviation from the surgical protocol, and elevated ESR before final bone graft procedure. As for IMT outcome, a comparative retrospective analysis through multivariate analysis of 54 patients with mono- and polymicrobial infections states that polymicrobial infection affects the infection recurrence rate (not failure) in treating femoral and tibial bone defects with the Masquelet technique[48]. There was no significant difference in the failure rate between mono- and polymicrobial infections. Moreover, the need for soft-tissue reconstruction and the infection recurrence rate was significantly higher in patients with polymicrobial infections that required reoperation. Another study found that 69% of cases with septic nonunion of tibial or femoral fractures treated with the two-step surgical protocol at a specialized bone infection facility achieved bone union and infection eradication within about 13.2 months after the second stage of the IMT procedure[46]. There were seven failures: five amputations due to mechanical and/or infection-related failure and two failed unions.

Deformities and residual limb discrepancy were reported in both aseptic and septic nonunion along with implant failures, graft resorption, wound infection, donor site pain, and amputations[4,9,15,25,34,45-50]. The rate of secondary lower limb osteotomy reveals the difficulty of maintaining good alignment with a single-plane fixator. Therefore, in severe defect (> 20 cm), a circular or hybrid external fixator was preferable to a single-plane model[4,9,12].

Ongoing modification of the IMT

IMT modifications largely depend on the bone defect size and associated infection for infection arrest and regeneration promotion[5,20].

Some have become an established practice already: (1) An antibiotic-impregnated spacer as a local infection fighter is now an overall practice; (2) Internal fixation as a stabilization method at stage 1 is more preferred; and (3) Allograft bone, if available, is used for graft expansion in massive defects.

Other modifications have been proposed and may need further research: (1) The two stages wrapping IMT for treating atrophic and recalcitrant aseptic nonunion[51]; (2) Autobone + vancomycin impregnated calcium sulfate calcium phosphate composites (3:1)[28]; (3) Reinforced spacer (flexible nails) for large infected defects[29]; (4) Fibula transfer as a graft for extensive defects, including vascularized fibular graft[19,23,45,49]; (5) Osteoconductive scaffolds such as a polycaprolactone-tricalcium phosphate[52]; (6) 3D-printed cage in infected tibia[52]; (7) Osteoinductive factors: BMP[20,52]; and (8) 3D-printed titanium (porous) prostheses for repairing CBDs exceeding 10 cm in the tibial diaphysis and femur[33,37].

Our orthopaedic institution has a practice of combining the strong biological merits of IMT with the IBT for bone formation stimulation and developed a modified technology of their sequential use for post-traumatic defects and congenital pseudarthrosis of the tibia[7]. One of the subgroups in our study was seven adults after several previous failed surgeries and a history of infection in six of them. Their mean post-traumatic tibial defects were 13.3% ± 1.7% from the contralateral side. We used only the first phase of the IMT procedure and the second step was IBT. Bone union was achieved in all patients and infection did not develop. The only disadvantage of this modification is long external fixation time due to spacer retention needed for membrane formation.

We would like to comment that porous titanium 3-D printed implants are able to quickly restore local anatomy and provide stable mechanical transmission[33,37]. Its combination with an intramedullary nail provides mechanical dispersion and ensures micromobility. We believe that additive bone diaphysis implants for subtotal defects should be considered if the fastest possible rehabilitation is required. However, the prognostic probability of revision of such implant type is extremely high. Therefore, it is worth striving for maximum anatomical healing through development of biodegradable material for defect filling. In turn, this prompts the development of the techniques for stimulating bone formation.

Comparison of the results of lower limb long-bone defect treatment with the Masquelet vs the IBT

The IBT and the IMT are the two methods that have been used worldwide for the conditions of aseptic and septic bone nonunion and defects due to their ability to stimulate bone regeneration and healing with autologous biological tissues[7]. Being specialized in nonunion and defect management with these techniques, the authors feel the necessity to comment on a few literature reports available on their comparison.

The two comparative studies involving 65 patients with composite tibial and soft-tissue defects[47] and 39 patients following post-traumatic osteomyelitis of the tibia[53] describe two different clinical situations. The first concluded that IMT is a better choice of treatment for open tibial and soft-tissue defects in Gustilo IIIB/C fractures. The IBT is the preferred option when the tibial bone defect is large or if the surgeon's expertise in microsurgery is limited. The other found that both IBT and IMT can lead to satisfactory bone results for managing post-traumatic osteomyelitis of the tibia. However, the IMT had better functional results, especially in femoral cases. The authors opine that IBT should be preferred in cases of limb deformity and IMT may be a better choice in cases of periarticular bone defects.

One randomized controlled trial compared management of infected tibial nonunion[30] with 29 participants and found that the functional and bone results were comparable but more reliable in the IBT than in IMT. The fixator duration and incidence of nonunion were higher in the IMT group. The IBT should be preferred in infected nonunion of the tibia with bone loss up to 6 cm.

Outcomes of large segmental infected tibial shaft defects were reported in 37 studies treated with bone transport techniques (n = 23), the Masquelet technique (n = 7), and vascularized fibular grafts (n = 7)[54]. Bone union was achieved in 94.3%, 89.5%, and 96.5%, respectively. Infection recurrence rates respectively were 1.6%, 14.4% and 7.0%. Complications per patient were 1.58, 0.78, and 0.73. However, the reviews on these techniques applied to infected cases stress the paucity of data that could directly compare their outcomes[55-57].

There is no universal agreement on which strategy a surgeon should choose. We encountered only one study that recommended tactical solutions for post-traumatic diaphyseal segmental bone defects[6].

Some final discussion points

A steady growth in the publications on IMT application has been noted recently. We attempted to review a great number of studies that had been undertaken to show its use and outcomes in aseptic and septic defects of the lower extremities. With all due respect to their authors and the work they have done, the heterogeneity of clinical groups in those studies creates the impression of IMT effectiveness in a wide range of pathological conditions. Considering the fact that those studies are predominantly a retrospective clinical material and the samples in the studies are small, it can be assumed that the authors presented their own experience of treating the most complex cases that are united essentially by the severity and rarity of the pathology. On the other hand, a lot of fundamental differences may be encountered in one and the same study (infected and non-infected cases, average outcomes for mixed groups, different segments, different anatomical areas of the segments, different types of implants, and different methods of autologous grafting) that pose bias to the conclusions.

Our reference list of the works of managing aseptic nonunion is much smaller than the one of the septic one. Moreover, most works present both conditions as one sample. Therefore, the comparative analysis of the IMT use in infected and non-infected cases currently cannot be complete. However, it allows us to observe the trends in the development of the technique and its evolution.

Probably, the most fundamental difference able to have an impact on the results of treatment is bone infection. It is this reason that prompted us to undertake this review. Based on the fact that the IMT method has a history of several decades, we hypothetically considered that a large experience accumulated within this period would allow us to compare and analyze the use of IMT in aseptic and septic bone defect conditions. Searching for studies with homogeneous material, we encountered the absolute dominance of IMT in the field of bone infection. The primary cause of this fact is the widespread and steady growth of infectious complications in the surgical treatment of severe fractures. Moreover, we should mention the transformation of the author's technique. Masquelet A, as a pioneer of the method, questioned the use of antibacterial drugs in the spacer in order to exclude their possible negative impact on the formation of the membrane and on adequacy of surgical debridement.

However, in bone infection, one of the primary tasks of cement spacers is local delivery of antibiotics to the pathological focus. Although the main and most frequently used material in the IMT method is PMMA, the accumulated experience of using a PMMA spacer between bone fragments for IM formation and delivery of antibacterial drugs revealed a number of its disadvantages. The main ones are: (1) The kinetics of release of antibacterial drugs from the material as their highest concentration is observed during the first days after implantation[58,59]; and (2) The need for PMMA removal that requires an additional operation. These shortcomings have prompted the search for new materials for filling bone defects that would provide prolonged release of antibacterial drugs in therapeutic doses and ways to avoid stage 2. At the moment, such materials are undergoing preclinical trials in vitro and in vivo[60,61]. The primary task is finding such materials for septic bone defects. In aseptic conditions, the kinetics of antibacterial drug release in the first days after spacer implantation seems sufficient to prevent infectious complications. Moreover, it is assumed that the biomembrane features antimicrobial activity related to the synthesis of antioxidants which are secreted along with growth factors and local peptides in the membrane which are able to inhibit secretion of the bacterial biofilm[7].

One of the promising areas of IMT applications is acute defects that are associated with open fractures[17-19]. In acute bone loss, the IMT does not offer a wait-and-see tactics of external fixation for primary soft-tissue cover of bone fragments and wound healing thus allowing further bone reconstruction later. On the contrary, it focuses on the coverage of soft-tissue defects and bone loss filling within one continuous tactical chain, forming a fairly specific time frame for patient's recovery. But it is worth noting that such treatment requires equally high qualifications of the surgeon and full material support at the hospital. Soft-tissue defects may need the skills of a plastic surgeon in order to use vascularized flaps, especially in tibial injuries with soft-tissue deficiency.

The general conclusions that may be drawn from the literature reviewed by us are: (1) IMT showed its efficacy in cases of non-infected and infected bone long-bone defects. The IMT management of the infected tibia prevails; (2) The cases reported in the reviewed by us clinical studies are mainly infected nonunion or severe open fractures with the risk of contamination. In these situations IMT gives a chance for infection arrest after thorough debridement within the waiting period during stage 1; (3) Most authors prefer internal fixation to avoid the risks of external fixation complications such as a higher pin-site infection rate. Opening the nonunion site, the surgeon can adequately resect non-vital tissues, which is especially important to prevent bone auto- or allograft lysis due to reinfection; (4) The union rate observed in the studies is rather high, especially taking into consideration that there is high prevalence of infectious etiology among the cases reported; (5) Infection recurrence is a major factor that determines IMT failure; (6) Aseptic defects less than 2 cm require one-stage treatment without IMT but the "diamond concept" as maximum stimulation means; (7) In bone infection, the use of a spacer rises no doubt but in the case of atrophic pseudarthrosis a more differentiated use of the IMT technique is necessary that would include cases of low-gradient infection, extensive defects requiring the addition of allograft bone, and history of failed one-stage plastic surgery; and (8) Minimum period of spacer placement of 4 to 6 weeks for aseptic nonunion is recommended; the longer periods are obviously determined solely by problems in the administration of treatment stages.

Based on the discussed above drawbacks of material presentation in the studies, we would like to suggest that future reports on IMT application adhere to certain algorithm of material, methods and outcome description.

Material: Sufficient number of patients for each segment treated, data on duration of the disease and its etiology.

Stage 1: Location and defect size after debridement; microbial cultures detected, quantity and name of the antibacterial drug mixed with PMMA; duration of antibiotic therapy, reasons for choosing antibiotics, administration regime, its correction if required after obtaining intraoperative tissue cultures; fixation option at stage 1; complications and relapses of infection, measures to stop them after stage 1, interval between stages 1 and 2.

Stage 2: Grafting and/or implantation options; name; duration of antibiotic therapy, reasons for choosing definite drugs, their administration regime; fixation option, consolidation period, union and nonunion rates, complications and recurrence of infection, measures to stop them after stage 2, amputations, functional and emotional state after the treatment.

CONCLUSION

The studies show that the IMT has been globally used in aseptic and osteomyelitic defects due to its clinical effectiveness and affordable nature. Despite several disadvantages, the IMT is a powerful strategy that can be applied successfully to very severe injuries or nonunion requiring simultaneous bone infection arrest and multi-tissue reconstruction in the situations where external fixation is inappropriate or risky. Authors’ variations and improvements in its practical implementation indicate the ongoing development and the interest of researchers in this technique.

ACKNOWLEDGEMENTS

The study was performed within the framework of the state assignment for research on the topic at the institution of the authors: Development of temporary bioresorbable antibacterial carriers for the management of post-osteomyelitic bone defects of the lower extremities.