DO COBALT-CHROMIUM FEMORAL HEADS HAVE HIGHER REVISION RISK COMPARED TO STAINLESS STEEL METAL HEADS WITH A SINGLE CEMENTED FEMORAL DESIGN? A NEW ZEALAND JOINT REGISTRY STUDY

Introduction In primary total hip arthroplasty (THA), the Exeter V40 femoral stem (Stryker, USA) can be implanted using either low friction ion treated cobalt-chromium (LFIT-CoCr) or stainless steel (SS) metallic heads. LFIT-CoCr is sometimes favoured by surgeons due to its higher Young's modulus and lower friction that is hypothesised to reduce wear. However, combining different metallic alloys (i.e. LFIT-CoCr head with SS alloy stem) has been associated with either increased corrosion or fretting at the head- neck junction. In addition, there is substantially higher cost with LFIT-CoCr heads. This registry-based study aimed to compare survivorship and reason(s) for revision between Exeter V40 femoral stems implanted using SS or LFIT-CoCr heads. Methods Using New Zealand Joint Registry data collected between 1999 and 2022, we identified 11,040 patients who underwent primary THA indicated for osteoarthritis using an Exeter V40/Trident or Exeter V40/Trident II hybrid combination with a highly crosslinked polyethylene (XLPE) liner and a metallic head. The groups were sub-divided into LFIT-CoCr (13.1%) and SS (86.9%) heads. Revision-free implant survivorship and functional outcomes (Oxford Hip Score [OHS]) were compared using adjusted Cox proportional hazard models. Results Revision-free implant survival at 10 years was 96.3% for LFIT-CoCr and 96.5% for SS heads. When compared with the SS group, there was no difference in the adjusted risk of revision for LFIT-CoCr group (Hazard ratio = 1.17, p=0.32). The most common indications for revision in both groups were firstly dislocation, then secondly deep infection. There was no difference in rates of aseptic loosening. Mean OHS scores were similar between groups at 6 months, 5 years and 10 years. Discussion and Conclusion Overall, survivorship outcomes were similar between LFIT-CoCr and SS metallic femoral heads and revision rates for osteolysis did not differ between groups. However, given the higher costs of the LFIT-CoCr implants, surgeons should consider using a SS head when using a Exeter/Trident hybrid THA with XLPE liner.