Do Cobalt-Chromium Femoral Heads Have Reduced Revision Risk Compared to Stainless-Steel Metal Heads with a Single Cemented Femoral Design? A New Zealand Joint-Registry Study

BACKGROUND: In primary total hip arthroplasty (THA), a stainless-steel (SS) femoral stem can often be implanted with either low-friction ion-treated (LFIT) cobalt-chromium or SS metallic heads. An LFIT head is sometimes favored for its higher Young's modulus and lower friction, thought to reduce wear. However, combining different metals (i.e., an LFIT head with an SS alloy stem) may increase corrosion or fretting at the head-neck junction. Furthermore, LFIT heads are more expensive in some markets. This registry-based study aimed to compare survivorship and reason(s) for revision between SS femoral stems implanted using SS or LFIT heads. METHODS: Using New Zealand Joint Registry data (between 1999 and 2022), we identified 11,040 primary THAs indicated for osteoarthritis using a SS polish tapered stem and highly porous titanium cementless cup combination with a highly crosslinked polyethylene (XLPE) liner and a metallic head. The groups were subdivided into LFIT (13.1%) and SS (86.9%) heads. Revision-free implant survivorship and functional outcomes (Oxford Hip Scores [OHS]) were compared using adjusted Cox proportional hazard models. RESULTS: Revision-free implant survival at 10 years was 96.3% for LFIT and 96.5% for SS heads. Compared with SS, the adjusted risk of revision for LFIT was not significantly different (hazard ratio = 1.17, P = 0.32). The most common indications for revision in both groups were dislocation and then deep infection. There was no difference in revision rates for trunnionosis. Mean OHS scores were similar between groups at six months, five years, and 10 years. CONCLUSION: Overall, survivorship outcomes were similar between LFIT and SS metallic femoral heads, and revision rates for osteolysis did not differ between groups. However, given the potential risk of taper junction tribocorrosion, surgeons should consider using an SS head when using a hybrid THA with an XLPE liner.