OUTCOME OF HYDROXYAPATITE-COATED NON-CEMENTED ANATOMIC FEMORAL STEMS

Abstract

Purpose: The purpose of this work was to evaluate the mid-term behaviour of 228 ABG-1 femoral stems implanted without cement in patients with at least five years follow-up.

Material and methods: The series included 228 ABG-1 (cup and femur) non-cemented hydroxyapatite-coated anatomic total hip prostheses implanted in 210 patients. Mean age was 62.2 years, 116 women, 112 men. Indications were: primary degenerative disease (53.6%), primary necrosis (21.5%), posttraumatic osteoarthritis (11.8%), rheumatoid disease (8.3%) and dysplasia (4.8%). A zincronium-polyethylene bearing was used for 200 hips (87.7%) and metal-polyethylene for 28. We retained for analysis 163 patients with mean 88.6 months follow-up [37 died without revision, 28 lost to follow-up (12.3%), 17 surgical revision]. The Postel Merle d’Aubigné (PMA) and Harris Hip Score (HHS) were noted. Radiographically, the AGORA Engh-Massin and ARA femur scores were determined; osteolysis was evaluated with the Gruen classification.

Results: The seventeen femoral revisions were related to aseptic loosening (n=4), fracture of the femur (n=4), sepsis (n=3), instability (n=3), pain (n=2), and limping (n=1). Overall survival was 92.5% at 88.6 months, relative survival (loosening) was 98.2%. At last follow-up, the PMA score was 17.3 and 92.7% of the patients had an excellent or good outcome (PMA > 14). The mean HHS was 96.4. Ninety-six percent of the patients were pain free. Radiologically, 112 stems were evaluated at last follow-up. The Engh-Massin classification showed that 102 stems presented certain bone ingrowth (85.2%), 15 suspected (12.3%), and two showed fibrous encapsulation with one case of implant instability. The ARA femur score was good or excellent in 70.5%, fair in 13.1%, poor in 16.4%. Hypertrophic cortical reaction was noted in Gruen zones 2–3 or 5–6 in 27.9% and was not correlated with pain. These reactions were however associated in more than half of the cases with a position anomaly in the frontal plan or an oversized stem. There was on incomplete pedestal and no extensive proximal stress shielding. Femoral osteolysis was very limited (mean surface area 145 mm2) in zones 1 and 7 in 21.3% of the cases. There were no cases of distal osteolysis.

Discussion: These data confirm the very good mid-term behaviour of the anatomic stems coated with hydroxyapatite. This metaphyseal coating acts like a barrier preventing diffusion of wear particles along the shaft. Stem migration was minimal, to the order of one millimetre, and did not continue beyond the first year. Over time, a constant trabecular metaphyseal endocortical bone reaction was observed, reflecting stress transmission to the proximal portion of the hydroxyapatite-coated femoral implant.