[Long term bone behavior in total primary hip arthroplasty with a fully hydroxyapatite-coated femoral stem: a continuous series of 120 cases with twelve years follow-up].

PURPOSE OF THE STUDY: Cementless hydroxyapatite-coated total prostheses have proven their reliability for more than twenty years. The intimate contact between the receiver bone and the implant allows "union" between the inert and living material. Osteointegration is maintained over time. The purpose of this work was to study the long-term reaction of femoral bone to wear debris after insertion of cementless hydroxyapatite implants.
MATERIAL AND METHODS: One hundred twenty implants constituted a continuous series of total hip arthroplasties performed since 1989 for primary joint degeneration in patients followed for at least twelve years. The same femoral implant totally coated with hydroxyapatite was used for all patients in combination with a metal cup and a polyethylene insert. Twelve years later, twenty-seven patients had died, five were contacted by telephone, and three were lost to follow-up, giving a study population of 85 total hip arthroplasties with complete review and radiographic data. Clinical and radiological findings are reported with a measure of polyethylene wear and femoral bone behavior in contact with femoral implants.
RESULTS: At twelve year follow-up, there were no cases of implant loosening. Clinical outcome was satisfactory, 90% of the hips were pain free. Radiologically, mean polyethylene wear was 0.1 mm per year with calcar changes (zone VII) in 27% and trochanter changes (zone I) in 14%. There was no evidence of osteolysis extension or granuloma formation in the shaft zone. Implant survival at twelve years was 99.1% (97.2-100%). DISCUSSION: Hydroxyapatite-coated cementless implants resist well to polyethylene wear debris. At twelve years, osteolysis caused by macrophage activation remained limited to zones I and VII. There appeared to be an intimate plug between the implant and the living bone preventing wear debris migration along the implant as was visualized along the entire length of the implant. Polyethylene wear was however real and the risk of osteolysis remains a threat to implant stability. Improved survival of hydroxyapatite-coated total hip implants will thus depend on improvements in the weight-bearing couple.