Abstract
Background/Objectives: Same day discharge (SDD) after Total Hip Arthroplasty (THA) is an important outcome in modern arthroplasty, yet no simple, reliable pre-operative prediction tool exists. This study aimed to develop and temporally validate a bedside scoring tool to estimate SDD probability for patients electively undergoing THR. Methods: A retrospective cohort of all elective primary unilateral THAs performed at a single orthopaedic National Treatment Centre between 2023-2024 (n = 1119) were analysed. SDD was defined as length of stay of zero days. Predictors included demographics, frailty, comorbidity, anaesthetic type and knife-to-skin time. Variable selection used complete-case LASSO (n = 804) followed by multiply-imputed pooled logistic regression (20 datasets). A simple 4-factor score of sex, age, anaesthetic type and knife to skin time was derived. Temporal validation was performed on an independent dataset from 2025 (n = 547). Results: The final 4-factor scoring system demonstrated excellent discrimination – AUC 0.83 – which was preserved in temporal validation – AUC 0.81. Calibration was good across both cohorts (Hosmer-Lemeshow p>0.5). Decision curve analysis showed a net benefit across clinically relevant thresholds. The optimal threshold was identified using Youden’s J (-2 points; sensitivity 0.86; specificity 0.64). The strongest indicators of SDD were general anaesthetic, and an earlier knife-to-skin time. Conclusion: This simple 4-factor scoring system gives clinicians an accurate, well-calibrated and clinically useful pre-operative prediction of SDD in elective unilateral THAs. Temporal validation supports its robustness. This scoring system has potential to alter clinical practice, inform list planning, and optimise resource allocation to maximise SDD potential.