Patterns and Risk Factors of Aseptic Loosening in a Hydroxyapatite-Coated Cementless Quadrangular Taper Femoral Stem: A Single-Center Cohort Study

Background There have been several reports of metaphyseal debonding of hydroxyapatite (HA)-coated cementless quadrangular taper femoral stems leading to revisions for aseptic loosening. This study aimed to assess the characteristics and risk factors of this type of revision. Methods A single-center cohort of total hip arthroplasty patients who received a cementless HA-coated Corail stem between 2006-2023 was identified. Cox proportional hazard models were used to estimate the hazard ratios (HRs) and confidence intervals (CIs) of the association between implant/patient characteristics and revision for aseptic loosening. Dorr type and canal fill was assessed for all patients undergoing revision. Results The study identified 3876 patients leading to 27 aseptic loosening revisions and 91 other revisions. Stem size <10 was associated with aseptic loosening, HR=9.1 (95% CI 3.4-24.2). Taller patients, metal-on-metal bearings, and collarless stems were all associated with higher risk. Half of patients with aseptic loosening had Dorr type A femurs and half had undersized stems. Initial radiographs showed little to no radiolucency for these patients. Radiolucency increased after several postoperative years. Only 20% of patients with other reasons for revision had undersized stems and these patients exhibited less radiolucency. Conclusions Smaller, undersized HA-coated cementless quadrangular taper stems appear to be at significantly increased risk of aseptic loosening in midterm follow-up. Surgeons using quadrangle tapered cementless stems should be cautious when broaching suggests a stem size smaller than preoperative templating recommended, especially in patients with narrow femoral canals and should consider using a collar whenever possible with this stem design.