The influence of hydroxyapatite coating on continuous migration of a Zweymuller-type hip stem: a double-blinded randomised RSA trial with 5-year follow-up.

Abstract

BACKGROUND AND PURPOSE\nAdding hydroxyapatite to a stem to enhance ingrowth is a matter of debate, even less is known about the long-term effect on stability by adding hydroxyapatite (HA). Continuous migration in the first 2-5\u2009years is an indicator of failed osteointegration or pending failure, enhancing the risk of loosening within 10\u2009years after initial surgery. We performed a double-blinded randomised RSA trial with 5-year follow-up, to compare and analyse migration characteristics of the hydroxyapatite uncoated (HA-) and hydroxyapatite coated (HA+) Zweymuller-type hip stem.\n\n\nPATIENTS AND METHODS\nIn this single-centre prospective randomised controlled trial 51 patients were randomised to receive either a HA- or a HA+ Zweymuller-type hip stem during total hip replacement. After 5\u2009years, 35 patients were still eligible for follow-up evaluation. The migration pattern was measured by use of radio stereometric analysis (RSA) images up to 2\u2009years to evaluate short-term migration, additionally RSA images were obtained 5\u2009years postoperatively to assess late-term and continuous migration. Furthermore, the improvement of clinical outcome was analysed by HSS and HOOS ADL and pain subscales preoperative and after 5\u2009years.\n\n\nRESULTS\nAfter initial settling of the implant, no significant migration occurred up to 5\u2009years post-surgery for HA+ as well as HA- prostheses. Continuous migration within the 2-5\u2009years time interval was not observed for both HA+ nor the HA- group in all directions (p\u2009<\u20090.05). No significant difference between both groups was observed (p\u2009<\u20090.10). In both groups the HHS and HOOS improved significantly at 5\u2009years compared to baseline for both groups. Improvement was not altered by the hydroxyapatite coating. No significant difference between both groups was observed (p\u2009>\u20090.58).\n\n\nCONCLUSIONS\nAddition of a hydroxyapatite coating did not influence the migration 5\u2009years postoperatively for the Zweymuller-type hip stem.Clinical Trial Protocol number: NL 23524.048.08.