Segmental bone loss represents a difficult clinical entity for the treating orthopedic surgeon. This article discusses the various treatment modalities available for limb reconstruction, with a focus on the indications, potential complications, and the outcomes of available treatment options.
Key points
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Critically sized defects are defined as smallest sized defects, in a specific bone and species of animal, which do not heal or undergo 10% regeneration. This condition generally occurs when the size of the defect is 2 to 3 times the diameter of the involved bone.
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The initial assessment of the patient with an injured extremity with bone loss should begin with Advanced Trauma Life Support (ATLS) protocol, focusing initially on resuscitation measures and determining whether the injured limb is salvageable.
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Initial fracture care should focus on thorough irrigation and debridement and fracture stabilization with either temporary external or definitive internal fixation.
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Defects less than 4 cm may be treated with autogenous iliac crest bone grafting. Defects between 3 and 7 cm may be treated with a bone shortening/relengthening procedure. Defects between 2 and 10 cm may be treated with autogenous bone graft obtained via the Reamer-Irrigator-Aspirator (RIA), or with distraction osteogenesis. Defects greater than 10 cm may be treated with vascularized fibular grafting.
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The RIA system allows for the procurement of greater than 50 cm 3 of bone graft rich in several growth factors.
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The Masquelet technique, although a 2-stage procedure, offers advantages such as local antibiotic delivery, mechanical stability, and production of a biomembrane that protects autograft resorption.
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Bone morphogenetic proteins (BMPs) may be used as treatment adjuncts and demonstrate equivalent efficacy and safety as autogenous bone graft. However, nonvascularized autogenous bone graft remains the gold standard for bone grafting.
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.
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.
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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 ).
