AN IN-VITRO STUDY OF PROXIMAL FEMORAL ALLOGRAFT STRAINS IN REVISION HIP-ARTHROPLASTY

Bone allografts are used frequently to replace bone stock subsequent t o total hip arthroplasty. Revision of the failed hip replacement resul ts in a complex structure of allograft bone, host bone and a metal fem oral component. To evaluate the mechanics of the allograft-implant-hos t bone structure at the time of surgery, a strain gauge study was unde rtaken with six fresh/frozen human femora. Under defined loading condi tions, cortical strain distributions were measured for five different cases: (I) normal bone, (2) bone with a femoral implant, (3) bone with the femoral component and an stem), (4) bone with an osteotomy and an implant cemented into the 'allograft' (i.e. the proximal end of the f emur), and (5) bone with an osteotomy and the implant cemented into bo th the proximal 'allograft' and the distal host bone. The results show ed that, prior to making the osteotomy, proximal femoral strains were decreased with the insertion of a change when the stem was cemented in to the proximal 'allograft' bone, or cemented into the proximal 'allog raft' and distal host bone. The decreases in strain for these test cas es 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 n ot change for all the different test cases, the decreased strains meas ured for the proximal 'allograft' suggested that the presence of the o steotomy causes the implant to undergo higher stresses for an applied load.