Factors affecting femoral bone remodeling after cementless total hip arthroplasty

We performed a postmortem comparison of femurs from two patients who had bilateral cementless total hip arthroplasties with femoral prostheses of different stiffness implanted in their right and left hips. Radiographs of transverse sections of the four femurs demonstrated that all the prostheses were bone ingrown with the most ingrowth occurring distally where the porous coating contacted diaphyseal bone. In both patients, dual-energy x-ray absorptiometry analysis revealed that the femur implanted with the stiffer prosthesis had a 65% to 79% greater loss of proximal periprosthetic bone than the femur implanted with the more flexible prosthesis. One patient, however, had a dramatically greater total loss of bone from side to side than the other patient. In this patient, we believe that it was host factors more than the differences in stem stiffness that affected the bone-remodeling pattern. Although the two femurs with the stiffer prostheses had the greatest bone loss, the two femurs with the more flexible prostheses demonstrated radiographic signs of cantilever bending of the prosthetic stem and failure of proximal osseointegration. We are not aware of any other bilateral human postmortem analysis that so clearly illustrates the effect of stem stiffness on bone remodeling.