Key points

Introduction

Significant bone loss may occur as a result of high-energy trauma, infection, tumor resection, revision surgery, and developmental deformities. This entity has a dramatic effect on both the surrounding soft tissue and the healing potential of the injured bone. Fracture nonunions occur for various reasons, and this well-established complication is quoted in the literature as having a 2.5% prevalence after long-bone fractures. However, in the setting of segmental bone loss, this rate approaches 100% secondary to the limited ability of the skeletal system to repair and fill defects. Based on several animal studies, critically sized defects are defined as the smallest sized defect, in a specific bone and species of animal, which does not heal or undergoes 10% regeneration; this is considered to be the case when the length of the deficiency is 2 to 3 times the diameter.

Treatment of large segmental bone defects presents a challenge for the treating orthopedic surgeon. Historically, management of these injuries consisted of amputation, which provided a short recovery period but resulted in a significant loss of limb function. At present, the focus of treatment has shifted toward limb salvage procedures and includes the following treatment options: bone shortening; distraction osteogenesis, the use of vascularized and nonvascularized bone grafts; and bone substitutes. This article reviews the various treatment strategies available for the management of critically sized defects in lower extremity trauma.

Introduction

Significant bone loss may occur as a result of high-energy trauma, infection, tumor resection, revision surgery, and developmental deformities. This entity has a dramatic effect on both the surrounding soft tissue and the healing potential of the injured bone. Fracture nonunions occur for various reasons, and this well-established complication is quoted in the literature as having a 2.5% prevalence after long-bone fractures. However, in the setting of segmental bone loss, this rate approaches 100% secondary to the limited ability of the skeletal system to repair and fill defects. Based on several animal studies, critically sized defects are defined as the smallest sized defect, in a specific bone and species of animal, which does not heal or undergoes 10% regeneration; this is considered to be the case when the length of the deficiency is 2 to 3 times the diameter.

Treatment of large segmental bone defects presents a challenge for the treating orthopedic surgeon. Historically, management of these injuries consisted of amputation, which provided a short recovery period but resulted in a significant loss of limb function. At present, the focus of treatment has shifted toward limb salvage procedures and includes the following treatment options: bone shortening; distraction osteogenesis, the use of vascularized and nonvascularized bone grafts; and bone substitutes. This article reviews the various treatment strategies available for the management of critically sized defects in lower extremity trauma.

Initial management

The initial approach to the traumatized limb with associated bone loss should follow the ATLS protocol. Once the primary survey is completed and resuscitation measures have been initiated, the secondary survey in then commenced. During this phase of the protocol, an assessment of whether or not the injured limb is salvageable is made.

Once limb salvage has been decided, the injured extremity should undergo thorough irrigation and debridement and initial fracture stabilization. The initial debridement may result in further loss of soft tissue and/or bone when grossly contaminated and devitalized tissue is removed. A plastic surgeon should be consulted in the initial phases of care to assist in definitive soft-tissue coverage. In cases in which a plastic surgeon is unavailable, negative pressure wound therapy may be used to initially manage wounds with significant soft-tissue injury ( Fig. 1 ). In addition, antibiotic-impregnated polymethylmethacrylate (PMMA) cement beads may be used at this stage to manage dead space created after removal of all dead or nonviable tissue ( Fig. 2 ). The use of antibiotic beads also allows for local antibiotic delivery at the site of injury. In most cases with significant soft-tissue and bone loss, a temporary external fixator provides initial fracture stabilization (see Fig. 2 ). However, in those cases in which bone loss is limited and the condition of the soft tissue is favorable, definitive internal fixation may be a primary option.

Negative pressure wound therapy (NPWT) use in a grade IIIB open tibia-fibula fracture with associated degloving injury from all-terrain vehicle crash. ( A ) Clinical photograph demonstrating significant soft-tissue injury. ( B ) Clinical photograph demonstrating the use of NPWT as initial strategy for temporary wound coverage.

Dead space management of an open fracture with antibiotic cement beads. ( A ) Significant comminution as a result of a gunshot injury to the tibia. ( B ) Significant bone loss and soft-tissue injury. ( C ) Use of antibiotic beads in the area of bone loss. ( D ) The injury was initially stabilized with an external fixator.

Immediate bone shortening

Immediate limb shortening and lengthening has been described for the management of longitudinal bone defects with or without soft-tissue loss due to different causes. This method not only allows for the management of bony defects but also assists in soft-tissue coverage by reducing the defect size or soft-tissue tension. Therefore, immediate shortening with subsequent progressive lengthening of the bone is an accepted treatment alternative for those who have absolute or relative contraindications for free or local flaps. In addition, this method results in an inherently stable facture pattern that allows the patient to walk and bear weight soon after surgery. Furthermore, this active and functional management can shorten the treatment time and reduce costs and absence from work. The degree of shortening that can be tolerated is multifactorial and depends on the following: the bone involved, the location within the bone itself, and whether it is a 1-bone segment (eg, humerus or femur) in which shortening is better tolerated or a 2-bone segment (eg, radius and ulna, tibia and fibula). With respect to the bone involved, immediate shortening of the upper extremity is tolerated well, as limb length discrepancy does not significantly alter function.

In the tibia and humerus, immediate shortening can be performed for defects of 3 to 4 cm and in the femur for defects of 5 to 7 cm. Femoral shortening may also be managed with compensatory shortening of the contralateral extremity, especially in patients with more than average height.

Bone defects less than 3 cm can usually be acutely shortened. Acute shortening of greater than 3 cm may be safe if the result of the vascular physical examination does not change. However, acute shortening of greater than 4 cm may result in venous congestion, edema, tissue necrosis, and infection. In situations in which the defect is too large to close immediately, gradual shortening (5 mm/day) may be undertaken to avoid any untoward complications.

Distraction osteogenesis

The first successful bone lengthening was reported by Codivilla in 1905, who described the osteotomy of a cortex and the application of an immediate traction force via a calcaneal pin. In 1913, Obredanne was the first to use an external fixator for limb lengthening. However, it was Ilizarov, in the 1950s, who developed the modern-day technique of distraction osteogenesis. This technique refers to the production of new bone between vascular bone surfaces created by an osteotomy and separated by gradual distraction.

The basic components of distraction osteogenesis include the following:

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  Use of an external fixator that affords stability and applies corrective forces that produce lengthening, angular correction, or transportation of bone.

  
  
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  A corticotomy, defined by Ilizarov as a low-energy osteotomy of the cortex, with preservation of the blood supply to the both periosteum and medullary canal.

  
  
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  A postoperative period

  
  
  
  
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    This period may be divided into 3 consecutive periods: latency, distraction, and consolidation.

    
    
    
    
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      The latency period is the time from corticotomy until distraction begins and ranges between 3 and 10 days. This period is generally thought to enhance bone formation.

      
      
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      During the distraction period, the apparatus is adjusted by 1 mm per day at a sequence of 0.25 mm 4 times per day.

      
      
      
      
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        Clinical studies have confirmed that this technique promoted osteogenesis in humans, but it was noted that the rate and frequency of distraction may have to be adjusted depending on factors such as the quality of bone formation and the response of the soft tissues.

      
      
      
      
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      The final and longest phase is the consolidation period.

      
      
      
      
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        During this period, the newly formed bone in the distraction gap is allowed to bridge and corticalize. The external fixation index denotes the number of days the external fixator is attached to the bone per centimeter of length gained. This index is typically 30 days per centimeter of length gained. The bone healing index is the time to union in months divided by amount of lengthening in centimeters.

      
      

    
    

  
  

This technique offers many advantages when used to treat bone defects in the lower extremity. It has the ability to correct deformity and lengthen an extremity; it eliminates donor site morbidity seen with autologous grafting or free tissue transfer. It allows the patient to remain ambulatory, as it enables early weight bearing and active range of motion. In addition, it may be used to treat massive bone loss ranging from 2 to 10 cm in size ( Fig. 3 ).

Ilizarov bone transport as a method for reconstruction of a massive skeletal defect in a grade IIIB open tibia-fibula fracture after motorcycle crash. ( A ) Initial radiograph and three-dimensional reconstruction computed tomographic scan demonstrating a comminuted distal tibia-fibula fracture with significant tibial bone loss. The injury was initially managed with irrigation and debridement and placement of an external fixator. The wound was managed with delayed primary closure during the initial hospitalization. No soft-tissue flap was required in this particular case. ( B ) The area of traumatic bone loss was subsequently managed 10 weeks after initial injury with a bone transport procedure. ( C ) Postoperative radiograph 10 weeks after initial injury demonstrating conversion of the external fixator to a bone transport ring fixator (Smith & Nephew, Memphis, TN, USA). A proximal tibial corticotomy is noted, as well as a distal antibiotic cement spacer block, which was removed 6 weeks later. After 4 months, autogenous iliac crest bone grafting of the docking site was performed. ( D ) Postoperative radiograph demonstrating bone regeneration proximally and a clinical photograph after autogenous iliac crest bone grafting of the docking site. ( E ) Postoperative radiograph after frame removal 11 months later demonstrating bone consolidation proximally at the corticotomy site and union at the docking site distally.

Despite these advantages, this technique requires long-term placement of external fixators and may be associated with complications. Neurovascular damage is a potential immediate complication but may be avoided with a thorough knowledge of anatomy. Frame-related complications are the most common and include pin tract infections, broken wires, and joint contractures. Patient intolerance of the frame is also another important factor to consider. Distraction osteogenesis using the Ilizarov technique requires almost 2 months in fixation for every centimeter of defect reconstructed in a single level transport. Therefore, there should be extensive preoperative education of the patient and the family to increase compliance, as the treatment is lengthy and painful.

After frame-related complications, the second most common complication is nonunion at the docking site. Several options exist to augment and enhance union at the docking site, including autologous bone graft, shingling or reshaping of the bone edges, bifocal transport over an intramedullary IM nail, secondary IM nailing, and application of low-intensity pulsed ultrasound.

In general, good results have been achieved with the use of the Ilizarov fixator. Studies have shown it to be a reliable method to treat segmental bone loss, with researchers reporting between 75% to 100% success. Despite these results, the Ilizarov system uses hinge and translation mechanisms that are specifically oriented for a given case and requires sequential correction of multiaxial deformities. Because of this, there is a steep learning curve in using the Ilizarov system.

The Taylor Spatial Frame (TSF) (Smith & Nephew, Memphis, TN, USA) is a multiplanar external hexapod frame that consists of 2 rings or partial rings connected by 6 telescopic struts at special universal joints. The TSF offers many advantages including reliability and the versatility to simultaneously correct rotation, angulation, and translation deformities by adjusting the strut lengths. Several clinical studies have reported favorable outcomes with the TSF in terms of healing traumatic bone defects and deformity correction.

Nonvascularized bone graft options

Nonvascularized bone grafts remain the gold standard for autologous bone grafts, as they contain the 3 components necessary to promote or enhance bone regeneration. These components include osteoconductivity, osteoinduction, and osteogenicity. Possible donor sites include the iliac crest, distal femur, proximal tibia, fibula, distal radius, and olecranon. The iliac crest is the most common donor site and is facile to harvest. It offers advantages such as good-quality bone with a high concentration of progenitor cells and growth factors. However, its use may be limited to smaller defects ranging from 0.5 to 3 cm, and there may be significant morbidity with harvesting large quantities of bone. Several studies have shown high incidences of complications related to iliac crest harvest, including donor site pain and injury to cutaneous nerves resulting in painful neuromas. In addition, bridging large bone defects by avascular grafts involves creeping substitution, with cells migrating from the well-perfused resection and junction area into an almost acellular matrix. Therefore, the use of avascular grafts not only requires time but also bears a high risk for complications, including bone atrophy, transplant fracture, and nonunion.

Reamer-Irrigator-Aspirator

The RIA device (Synthes, West Chester, PA, USA) was originally designed as a simultaneous reaming, irrigation, and aspiration system to reduce the IM pressure, cortical heat generation, and systemic effects during IM nailing. The RIA device now offers an additional source of bone to treat traumatic bone defects ( Fig. 4 ).

Reconstruction of a skeletal defect with the use of the Reamer-Irrigator-Aspirator (RIA) in a grade IIIB open tibia-fibula fracture in a pedestrian stuck by an automobile. The injury was managed initially with irrigation and debridement and external fixation. ( A ) Clinical photograph and radiograph demonstrating temporary stabilization with an external fixator. Note both the degree of soft-tissue injury and bone loss. Three days after initial presentation, repeat irrigation and debridement was performed and the area of bone loss was managed with antibiotic beads. ( B ) Repeat irrigation and debridement procedures were performed during a 1-week period, and the injury was stabilized definitively with an intramedullary nail and syndesmotic screws. An antibiotic cement spacer block was also used. ( C ) After 7 weeks, the cement spacer was removed and autogenous femoral canal bone graft was harvested with the RIA system. ( D ) Postoperative radiograph after autogenous femoral canal bone grafting. ( E ) Postoperative radiograph 18 months after autogenous femoral canal bone grafting demonstrating union at the area of bone loss.

This method of obtaining bone graft is quite practical, as the IM canals of the femur and tibia are easy to access and contain large amounts of cancellous bone graft. In addition, the biological content of the RIA graft has been shown to be superior to iliac crest bone graft (ICBG), and the volume available is regularly 50 cm ³ or more. Research comparing the quantitative levels of growth factors from RIA aspirate, ICGB, and platelet preparations found higher levels of 5 of 7 growth factors obtained from IM reamings compared with iliac crest graft. These growth factors included fibroblast growth factor, platelet-derived growth factor, insulinlike growth factor, BMP, and transforming growth factor (TGF).

Studies have shown the utility of RIA bone graft in treating bone defects. McCall and colleagues reported on large segmental bone defects treated with RIA bone graft. The average defect size in their study population of 21 patients was 6.6 cm, and 85% of the defects were healed at 11 months. However, 7 of the 17 healed defects required additional surgery. Stafford and Norris treated 25 patients with 27 segmental defect nonunions with RIA graft. The overall average segmental defect measured 5.8 cm in length, and at 6 months and 1 year postoperatively, 70% and 90% of the nonunions were healed both clinically and radiographically.

Although there are many reports on the potential benefit of the RIA graft, there are concerns about the mechanical changes that occur in the donor femur after graft harvesting. For example, its use in the elderly is one that should be exercised with caution because of reduced cortical thickness and potential for postoperative fracture. Lowe and colleagues reported a case series of postoperative fractures that occurred after RIA graft harvesting and suggested the following:

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  Preoperative assessment of cortical diameters at long-bone harvest sites

  
  
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  Careful monitoring during intraoperative reaming

  
  
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  Avoidance of RIA bone graft harvesting in patients with a history of osteoporosis or osteopenia unless postharvest IM stabilization is considered

Others have demonstrated that attention must be paid to technique as eccentric femoral reaming either proximally or distally may result in catastrophic failure.