Radius of proximal femur curvature as a significant predictor for long stem-canal match in total hip arthroplasty: a retrospective cohort study

BACKGROUND: The match between femoral stems and the medullary canal is crucial for successful total hip arthroplasty (THA), particularly for long stems often used in complex primary and revision surgeries. This study aimed to investigate the association between the radius of proximal femur curvature (RPFC) on long stem-canal match in THA. METHODS: In this retrospective study, 65 patients who underwent revision or complex primary THA using a 200 mm long stem between June 2019 and June 2024 were analyzed. Preoperative CT scans were used to measure RPFC and bone volume fraction (BV/TV). Stem-canal match was assessed using postoperative radiographs. Multivariate logistic regression and ROC curve analyses were performed to evaluate the predictive value of RPFC for stem-canal match. RESULTS: Significant differences in RPFC were observed between the match and mismatch groups (656.0 ± 198.9 mm vs. 401.4 ± 73.3 mm, p < 0.001). Height and gender also differed significantly between groups in univariate analysis. After adjusting for height and gender in a multivariate logistic regression model, RPFC remained an independent protective factor against stem-canal mismatch (OR = 0.98, 95% CI: 0.97-0.99, p < 0.001). ROC analysis revealed an optimal RPFC cut-off value of 496.4 mm for predicting good stem-canal match (sensitivity: 94.4%, specificity: 85.1%, AUC = 0.923). Compared to height (AUC = 0.725) and gender (AUC < 0.7), RPFC demonstrated superior predictive value for stem-canal match. CONCLUSION: RPFC is a significant predictor of long stem-canal match in THA. An RPFC < 496.4 mm is associated with a higher risk of mismatch for the implant used in this study. While these findings are promising, this is a single-center study with a limited sample size. Further, larger prospective studies are needed to validate these conclusions before widespread clinical adoption can be recommended. Preoperative RPFC measurement shows potential to improve implant selection and reduce mismatch-related complications in THA.