Purpose: The purpose of this work was to study the radiological outcome more than seven years after implantation of 89 anatomic non-cemented femoral stems with hydroxyapatite coating around the metaphyseal circumference.
Material: These 81 patients underwent primary arthroplasty (89 hips) between 1991 and 1994 for joint degeneration or necrosis: 48 men and 33 women, mean age 59 years (range 41–78). The inclusion criteria for this study were physical examination and complete radiographic work-up in the second half of 2001. Mean follow-up was nine years (range 7–10).
Methods: All x-rays were analysed by four independent surgeons who used the Engh and Massin criteria. The evaluators, who had not participated in patient care, made their assessment on the basis of the last follow-up clinical report and x-rays. They search for radiographic evidence of stem stability and bony integration as well as signs of osteolysis using the Gruen criteria.
Results: At last follow-up only one femoral stem was painful, but stable. This stem was revised at seven years. Six cups had been changed due to polyethylene wear with iliac osteolysis but without femoral participation. There were no other reoperations. Polyethylene wear was observed in about one-half the hips (44 hips) and was considered severe (1–2 mm) in nine cases. There were no lucent lines nor reactive lines in the metaphyseal area (zones 1 and 7) but 16% of the hips presented reactive lines along the lower, smooth, part of the stem. Endosteal ossification was observed in zones 2 and 6 in 72% of the hips, and less often (13%) in zones 9 and 13. Five hips (5.6%) exhibited bony growth at the tip of the stem producing a thickening in zone 5; these were the only cases with cortical thickening excepting the revised stem (thickening in zones 2 and 6). There was no case of cortical narrowing. Calcar atrophy was observed in 42 hips (47%) with five showing a “drop” aspect. Four hips exhibited osteolysis of the proximal femur in zone 1A, but there were no images of distal osteolysis of the femur.
Discussion: This independent analysis of 89 x-ray files demonstrated that endosteal growth is frequent in the isthmic region. The radiological tolerance was good for this stem (no cortical changes) but there were modifications of the calcar which were difficult; it could be speculated that certain of these modifications might correspond to localised osteolysis at the lowest part of the joint, migration point of polyethyene debris. The role of hydroxyapatite in the observed absence of distal osteolysis is noteworthy.
Conclusion: At nine years follow-up, the absence of osteolysis of the distal femur despite usual polyethylene wear allows the conclusion that hydoxyapatite coating of the metaphyseal circumference creates an effective barrier against wear debris.
