FIRST REVISION TOTAL HIP ARTHROPLASTY FOR INSTABILITY: TEN-YEAR OUTCOMES AND RISK FACTORS ASSOCIATED WITH FAILURE

There is conflicting data on the long-term survivorship following revision THA for instability. The aim of this study is to assess the survivorship of the first revision THA when undertaken for instability and identify patient and surgical factors associated with failure. Institutional Review Board approval was obtained for this retrospective cohort study from a tertiary referral centre in an academic hospital. There were 678 patients undergoing revision THA for instability during the period 01/01/2000 to 01/01/2022 identified from an institutional database. Of these cases, 290 (42.8%) were the index revision procedure (median age 65.9 years (inter-quartile range (IQR) 57–76); females 180 (62.1%); median body mass index (BMI) 28.1 (IQR 24.3–32.2)). The primary outcome of interest was re-revision surgery for instability. The mean time from surgery to the last follow-up date was 11.4 years (min 2 years to max 22 years). Re-revision was defined as addition or exchange of implants. Implant survivorship at 10 years, with censoring for death and loss to follow-up, was calculated using Kaplan-Meier estimates with 95% confidence intervals (CI). Multivariable Cox proportional hazard regression modelling was used to assess variables associated with 10-year survival and are reported as hazard ratios (HR) with 95% CI. The main patterns of hip instability were classified as malposition of the acetabular component (27.7%), impingement (36.7%) or late polyethylene wear (19.4%). The majority of revisions involved either modular exchange (liner + femoral head) (44.5%) or acetabular component revision with modular exchange (39.4%). At latest follow-up, there were 82 (28.3%) deaths, and 84 (29%) hips underwent at least one re-revision. The majority of failures (77.8%) occurred within 5 years of the initial revision surgery and the indications for re-revision were recurrent instability (66.7%), periprosthetic joint infection (13.3%), pseudotumour formation (8.9%), loosening and wear (6.7%) and periprosthetic fracture (4.4%). Ten-year Kaplan-Meier survivorship estimates were 80.0% (95%CI 73.4–87.3) for instability as the primary end-point (Figure 1) and 70.7% (95%CI 63.2–79.2) when considering all indications for re-revision THA. Modular component exchange alone was significantly associated with re-revision THA for instability compared to procedures which included revision of the femoral stem, acetabular component or both (HR 1.89 (95% CI 1.1–4.1), p = 0.02). Factors associated with increased re-revision risk within 10 years for any cause were younger age at surgery (HR 0.39 95%CI 0.19–0.75, p = 0.005) and using a constrained liner (HR 3.0 95%CI 1.3–7.3, p = 0.04). There is a high rate of recurrence within 10 years when the first revision THA is undertaken for hip instability. The risk of re-revision THA for instability was highest in patients undergoing modular component exchange alone. Use of a constrained liner was significantly associated with an increased all-cause re-revision risk within 10 years; however this may reflect unmeasured confounding as these implants are typically used in the highest risk patients. For any figures or tables, please contact the authors directly.