Reconstruction of bone defects after malignant tumor resection if often accomplished with fibular allograft. Fracture and nonunion are known complication of this technique. The following case will illustrate a method for treating a failed structural allograft utilizing autologous bone graft and external fixation. This is an alternative to salvage with a free vascularized fibular autograft.
This is a 30-year-old female who had resection of an osteosarcoma of the distal tibia as an adolescent. The defect was reconstructed with a fibular allograft which fractured and was augmented with bone graft and internal fixation. She presented with a long standing deformity of the lower leg and a nonunion of the tibia.
The strategy was for a staged approach to limb salvage. The first stage was a reconstruction of the nonunion with acute deformity correction, preservation of the allograft as a structural device, removal of the internal fixation, bone grafting with autologous iliac crest bone graft, and fixation with a circular frame that provided constant compression. The second stage was extension of the external fixator to the proximal tibia and osteoplasty of the tibia and fibula for limb length equalization.
Distraction osteogenesis requires adequate blood flow to the site of the osteotomy to ensure adequate regenerate bone formation. The proximal tibia provides an ideal environment for distraction to progress successfully. The distal tibia, in this patient, has been through multiple surgeries and the tibia is in a state of nonunion. These factors make attempting to distract through the same nonunion repair unlikely to heal. In other words an osteotomy through the nonunion with gradual correction and lengthening would likely lead to a persistent nonunion. Therefore, proximal tibia osteotomy is preferred to ensure success.
In order to obtain small morsels of iliac crest bone graft the acetabular reamer was used on the outer table of the iliac crest. The crest was reamed down to the inner table. The reamings were collected and additional cancellous graft was harvested with curettes.
With correction of the varus-procurvatum deformity and debridement of poorly vascularized bone at the nonunion site the extensor tendons became lax and a functional drop foot ensued. Later lengthening of the tibia re-tensioned these tendons and led to a full functional recovery.
Infection of the retained fibular allograft through a pin site infection was a concern unique to this case. To prevent deep infection the pins and wires were placed outside of the graft zone, and the patient was kept on oral antibiotics the duration of the reconstruction.
When the patient developed dorsiflexor tendon laxity the foot was protected with a neutral foot splint to prevent equinus contracture. Daily ankle and knee exercises helped ensure free joint motion during the lengthening.
Rh-BMP (Recombinant human bone morphogenic protein) was avoided due to the history of local bone cancer for fear of recurrence.
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