Extracortical Bone-Bridging Fixation with Use of Cortical Allograft and Recombinant Human Osteogenic Protein-1

Abstract

Prosthetic reconstruction with extracortical bone-bridging fixation is an effective method for the treatment of massive bone loss. We evaluated the effect of the use of recombinant human osteogenic protein-1 (rhOP-1) combined with allogenic cortical bone strips as a substitute for an autogenous bone graft for extracortical bone-bridging. Eight skeletally mature adult male dogs underwent a bilateral resection of a 6-cm segment of the femoral diaphysis and reconstruction with a porous segmental prosthesis. On the experimental side, an allogenic cortical onlay graft in the form of bone strips combined with rhOP-1 mixed with bovine type-I-collagen putty (OP-1 putty) was applied. On the control side, allogenic cortical bone strips augmented with autogenous cancellous bone chips and bone marrow were used. The reconstructions were followed for twelve weeks with biweekly evaluations of load-bearing gait and radiographs. The animals were killed twelve weeks after the surgery, and the reconstructed femora were studied biomechanically, histologically, and with microradiographs. One animal was excluded from the analysis because a fracture of the proximal part of the femur on the control side was observed radiographically twelve weeks after the surgery. There were no significant differences in load-bearing gait between the experimental and control sides throughout the experimental period. Serial radiographs revealed a 1.9-fold (p<0.04), 2.7-fold (p<0.01), and 2.4-fold (p<0.03) increase in mineralized area on the experimental side at two, four, and six weeks, respectively. The torsional stiffness and strength of the fixation attributed to the extracortical bridging bone alone were 2.3-fold (p<0.03) and 2.2-fold (p=0.058) greater on the experimental side, respectively. The allograft porosity on the experimental side was 3.8-fold (p<0.02) greater than that on the control side. With the number of samples available, there was no significant difference in mineral apposition rate between the experimental and control sides. In an animal model of segmental bone-replacement prosthetic fixation with use of the extracortical bone-bridging principle, an allogenic onlay cortical graft combined with rhOP-1 was an effective substitute for autogenous bone graft.