Abstract
Bone allografts are used frequently to replace bone stock subsequent to total hip arthroplasty. Revision of the failed hip replacement results in a complex structure of allograft bone, host bone and a metal femoral component. To evaluate the mechanics of the allograft-implant-host bone structure at the time of surgery, a strain gauge study was undertaken with six fresh/frozen human femora. Under defined loading conditions, cortical strain distributions were measured for five different cases: (1) normal bone, (2) bone with a femoral implant, (3) bone with the femoral component and an osteotomy at the mid-stem level of the implant (i.e. to simulate the proximal allograft-host junction around the femoral stem), (4) bone with an osteotomy and an implant cemented into the ‘allograft’ (i.e. the proximal end of the femur), and (5) bone with an osteotomy and the implant cemented into both the proximal ‘allograft’ and the distal host bone. The results showed that, prior to making the osteotomy, proximal femoral strains were decreased with the insertion of a femoral stem. These strains were further decreased when an osteotomy had been made. This strain distribution did not change when the stem was cemented into the proximal ‘allograft’ bone, or cemented into the proximal ‘allograft’ and distal host bone. The decreases in strain for these test cases implied that the discontinuity between the bony segments caused an extended reduction in the tensile or compressive stresses transmitted through the cortices. Since strains in the distal host bone also did not change for all the different test cases, the decreased strains measured for the proximal ‘allograft’ suggested that the presence of the osteotomy causes the implant to undergo higher stresses for an applied load.
Published Version
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