Hip resurfacing arthroplasty at a minimum of 14 years: revision is concentrated among female patients with dysplasia and small components.

INTRODUCTION: Hip resurfacing arthroplasty (HRA) is a bone-preserving option for young, active patients. The influence of the underlying diagnosis on long-term outcome remains unclear, particularly the distinction between primary osteoarthritis (OA), developmental dysplasia of the hip (DDH) and non-OA conditions. MATERIALS AND METHODS: We retrospectively reviewed 104 consecutive metal-on-metal HRAs in 101 patients (three bilateral) performed by one surgeon between 2006 and 2011, stratified into Primary OA (n = 50), DDH (n = 29) and Non-OA (n = 25: avascular necrosis [AVN] n = 15, inflammatory arthritis n = 5, post-traumatic arthritis n = 3, Legg-Calvé-Perthes disease n = 2). AVN was analysed additionally as an independent group, and exploratory analyses restricted to female patients and to cups ≤ 50 mm addressed the collinearity of dysplasia, sex and size. Survivorship used Kaplan-Meier estimation with revision as the endpoint. RESULTS: Implant status was known for all 104 hips; the 91 unrevised assessed hips had a mean follow-up of 16.2 ± 1.5 years. Overall 15-year survivorship was 95.2%. Primary OA, Non-OA and AVN each showed 100%; DDH 82.8% (versus Primary OA p = 0.002, versus Non-OA p = 0.031). All five revisions occurred in female DDH patients with a cup ≤ 50 mm; DDH survivorship remained lower within female patients (p = 0.025) and within small cups (p = 0.006), with no event in any comparator arm. Final HHS was lower in DDH (89.5 ± 8.5) than in Primary OA (93.9 ± 6.8) or Non-OA (95.0 ± 4.9; p = 0.012), a difference below the minimal clinically important improvement threshold of 15.9 to 18 points. The Co/Cr ratio did not differ between groups (p = 0.37). CONCLUSIONS: HRA achieved 100% 15-year survivorship in primary OA and in non-OA diagnoses including AVN. Dysplasia may be associated with an increased risk of revision, but dysplasia, female sex and small component size were too collinear, with no revision outside the dysplastic group, for their independent contributions to be separated.