Abstract
Introduction
The impact of pseudotumours associated with metal-on-metal hip resurfacings (MoMHRs) within the second decade is unknown. We investigated: (1) the incidence and risk factors for all-cause and pseudotumour revision following MoMHR at 15-years follow-up, and (2) whether risk factors were gender specific.
Patients and methods
This single-centre prospective cohort study included 1429 MoMHRs (1216 patients; 40% female) implanted between 1999–2009. All patients were contacted in 2010 and 2012 as per national recommendations. Patients with hip problems and/or suboptimal Oxford Hip Scores (<41/48) underwent cross-sectional imaging and blood metal ion sampling. Revisions were performed as indicated with diagnoses confirmed from operative and histopathological findings. Multi-variate Cox proportional hazard models assessed the association of predictor variables on time to all-cause and pseudotumour revision.
Results
Revisions were performed in 180 MoMHRs (111 for pseudotumour; 62%). Incidence and 15-year revision rates were 12.6% and 19.5% (95% CI 16.2%-23.2%) respectively for all-causes, and 7.8% and 14.0% (95% CI 11.0%-17.7%) respectively for pseudotumours.
Smaller femoral head sizes (Hazard Ratio (HR)=0.92 (95% CI 0.88–0.97), p=0.003) and implant design (HR=1.55–3.01, p<0.029) significantly increased all-cause revision risk. Female gender (HR=0.49 (95% CI 0.29–0.84), p=0.009) and young age (HR=0.98 (95% CI 0.96–1.00), p=0.020) also significantly increased pseudotumour revision risk but not all-cause revision risk. Risk factors for all-cause and pseudotumour revision were gender specific. In females, smaller femoral head sizes (p=0.014) increased all-cause revision risk, with young age the only predictor of pseudotumour revision (p=0.019). In males, implant design predicted both all-cause (p<0.015) and pseudotumour revision (p=0.001).
Discussion
Incidence and revision rates for all-cause and pseudotumour revision were high in the second decade following MoMHR. Revision predictors differed for all-cause compared to pseudotumour revision, and were also gender specific.
Conclusion
Current worldwide follow-up recommendations must ensure these factors are appropriately weighted when risk stratifying MoMHR patients for surveillance.
