Risk factors for revision of Birmingham Hip Resurfacing arthroplasty. A single-center study with a median 13-year follow-up.

Background: Consensus is lacking regarding follow-up after metal-on-metal hip resurfacing (MoM-HR). This study examines risk factors for revision and evaluates the need for sequential follow-up. Patients and methods: 288 consecutive patients operated on with a unilateral Birmingham Hip Resurfacing (BHR) 2001-2014, having at least one x-ray and one metal ion sampling, were followed until 2022. Hazard ratios (HR) of revision were calculated for sex, age, femoral component head size, implant positioning, serum cobalt (sCo), and serum chrome (sCr) concentrations. The relative risk (RR) of revision if risk factors were present was calculated. Radiologic changes in component positioning were analyzed in 288 patients, and metal ion changes in 147 patients. Results: The median follow-up was 13 years. Factors associated with revision were sCo and/or sCr >5 μg/l at first follow-up, a post-operative anteversion <5 or >25°, and femoral head component size <50 mm. Patients with one or more risk factors at first follow-up had a RR of 10 (95 % CI 2.5-42) to be revised compared to those without risk factors. A ≥10° change in the stem shaft angle was associated with an increased OR of revision (OR 14, 95 % CI 4.4-43). A change in sCo and/or sCr from ≤5 to >5 μg/l between follow-ups was associated with an increased risk of revision (OR 8.5, 95 % CI 1.3-55). Conclusions: Patients with risk factors at first follow-up, a change from serum metal ions ≤5 to >5 μg/l, and a ≥10° change in the stem shaft angle at sequential follow-ups warrant continuous follow-up even if asymptomatic.