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

Background and purpose: Adding 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 years is an indicator of failed osteointegration or pending failure, enhancing the risk of loosening within 10 years 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. Patients and methods: In 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 years, 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 years to evaluate short-term migration, additionally RSA images were obtained 5 years 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 years. Results: After initial settling of the implant, no significant migration occurred up to 5 years post-surgery for HA+ as well as HA- prostheses. Continuous migration within the 2-5 years' time interval was not observed for both HA+ nor the HA- group in all directions (p < 0.05). No significant difference between both groups was observed (p < 0.10). In both groups the HHS and HOOS improved significantly at 5 years compared to baseline for both groups. Improvement was not altered by the hydroxyapatite coating. No significant difference between both groups was observed (p > 0.58). Conclusions: Addition of a hydroxyapatite coating did not influence the migration 5 years postoperatively for the Zweymuller-type hip stem. Clinical Trial Protocol number: NL 23524.048.08

Automated summary

This study compared the migration characteristics of hydroxyapatite coated (HA+) and uncoated (HA-) Zweymuller-type hip stems through a double-blinded randomised RSA trial with a 5-year follow-up. The results showed that the addition of a hydroxyapatite coating did not influence the migration of the hip stem after 5 years, and there were no significant differences in clinical outcomes between the two groups.