Autogenous onlay grafting for enhancement of extracortical tissue formation over porous-coated segmental replacement prostheses

Background: Prosthetic reconstruction,vith extra-cortical bone-bridging is an effective method of limb salvage after resection of a malignant or local ly invasive benign bone tumor. Use of cancellous bone graft alone is less e ffective in achieving extracortical bone-bridging. The present study was pe rformed to investigate the effects of a corticocancellous onlay graft on bo ne and soft-tissue formation over a porous-coated replacement prosthesis in the mid-diaphyseal region of canine femora, Methods: Bilateral resection of a six-centimeter segment of the femoral dia physis and reconstruction with a porous-coated segmental prosthesis was per formed in six mongrel dogs, In one limb (the experimental side), eight stri ps of corticocancellous bone were evenly placed around the junctions betwee n the femur and the prosthetic surface. Cancellous bone was placed under an d between the strips of cortical bone. No graft was used in the other limb (the control side). The animals were followed for twelve weeks, with sequen tial assessments of load-bearing and radiographic evaluation, Biomechanical , histological, and microradiographic analyses of the specimens were perfor med after death. Results: On the control side, load-bearing at four weeks postoperatively wa s significantly decreased compared with the preoperative value (p < 0.05); no difference in these values could be detected on the experimental side, B oth the area of the callus and the contact area between the bone and the pr osthetic shoulder were greater on the experimental side (p < 0.05), The mec hanical stiffness and the maximum torque at failure of the extracortical br idging tissue across the junction between the bone and the prosthetic shoul der were eighteen (p < 0.007) and five times greater (p < 0.05), respective ly, on the experimental side. Conclusions: Extracortical bone-bridging was accomplished with corticocance llous onlay bone-grafting. Without bone-grafting, bone formed only occasion ally. Bone-grafting also enhanced the formation of a soft-tissue capsule ar ound the prosthesis.