MODELING OF BONE AROUND HYDROXYAPATITE-COATED FEMORAL STEMS

Two hundred and twenty-four total hip arthroplasties were performed in 201 patients with use of a femoral component with hydroxyapatite coat ing of the proximal portion of the stem, Tile mean duration of follow- up was seventy-one months (range, fifty-eight to eighty-seven months). Of the 224 arthroplasties, 208 (93 per cent; 190 patients) yielded a good or excellent clinical result, Four patients (2 per cent) reported mild-to-moderate activity-related pain in the thigh, and two (1 per c ent) had aseptic loosening, The radiographic findings of progressive n ew-bone formation (cancellous condensation and cortical hypertrophy) t hroughout the zones adjacent to the middle and distal portions of the stein Were evidence of early, extensive proximal fixation of the impla nt, with distal stress transfer through tile implant, which is stiffer than the surrounding bone, Remodeling of the femur began early was:pr edictable, and progressed throughout the follow-up period, Cortical hy pertrophy about the middle and distal portions of the stem occurred pr edominantly in the mediolateral plane (in 105 hips [47 per cent], comp ared with thirteen hips [6 per cent] in the anteroposterior plane), an d it was more common in patients who had had poorer bone quality preop eratively, Intramedullary osteolysis was present in one femur (0.4 per cent) at five years; the osteolytic area was less than Five millimete rs in ifs greatest dimension and had not progressed at the time of the six-year follow-up evaluation, This low rate of osteolysis suggests-t hat a circumferential coating of hydroxyapatite may effectively minimi ze migration of wear debris along the femoral stem. The progressive re modeling of the femur about the middle and distal portions of the stem , as evidenced by cancellous condensation and cortical hypertrophy, ha s not, to our knowledge, been described previously to this magnitude i n association with proximally coated (porous or hydroxyapatite-coated) femoral implants.