Pre-operative two-step test predicts reciprocal stair-climbing performance one week after total hip arthroplasty

Purpose The aim of this study was to identify pre-operative physical function and muscular factors that predict reciprocal stair-climbing performance 1 week after total hip arthroplasty (THA). Methods This retrospective cohort study included consecutive patients who underwent primary unilateral THA via a posterior approach between June 2024 and July 2025. At 1 week post-operatively, patients were classified into two groups based on stair-climbing performance: the reciprocal stair-climbing and the impaired stair-climbing groups. Pre-operative assessments included the two-step test (2ST), 30-second chair-stand test (CS-30), one-leg stance time, and computed tomography-based muscle cross-sectional area (CSA) and density [Hounsfield units (HU)]. The multivariable logistic regression model identified independent predictors of reciprocal stair-climbing performance. Results Of the 302 patients screened, 110 were eligible for analysis (38 in the reciprocal group and 72 in the impaired group). The reciprocal group demonstrated better CS-30, 2ST, and one-leg stance times. Although CSA did not differ between groups, the reciprocal group showed higher HU values in several muscles. Multivariable analysis identified the 2ST as the only independent predictor of reciprocal stair-climbing performance (per 0.1 unit increase, odds ratio 0.65, 95% confidence interval 0.48–0.88; p = 0.005). Receiver operating characteristic analysis identified an optimal 2ST cutoff value of 0.96 (AUC 0.76; sensitivity, 75.0%; specificity, 69.5%). Conclusions The 2ST is a simple and clinically useful tool, and a pre-operative cutoff value of 0.96 may help predict reciprocal stair-climbing performance 1 week after THA. Future longitudinal studies are needed to evaluate the relationship between early 2ST performance and long-term functional outcomes after THA.