Association of surgical timing with 30-day independent ambulation and postoperative sleep disorder in older adult patients undergoing joint replacement: an exploratory secondary analysis of a prospective cohort.

OBJECTIVE

This exploratory study investigated the observational association between surgical timing (morning versus afternoon) and 30-day independent ambulation in older adult joint replacement patients, and whether postoperative sleep disorder (PSD) mediates this association.

METHODS

This was an exploratory secondary analysis of a prospectively registered cohort. Patients aged ≥ 65 years undergoing joint replacement were included. Surgical timing was the exposure, 30-day independent ambulation the primary outcome, and PSD the potential mediator. Propensity score matching (PSM) was used to balance baseline characteristics, and a doubly robust sensitivity analysis was performed to address residual imbalance. Logistic regression and counterfactual mediation analysis were then conducted.

RESULTS

Among 753 eligible patients, PSM balanced most baseline characteristics. Afternoon surgery was significantly associated with higher odds of 30-day independent ambulation (OR = 2.106, 95% CI: 1.407-3.146, p = 0.001). The Natural Direct Effect remained significant (OR = 2.174, p < 0.001), while the Natural Indirect Effect via PSD was not significant (OR = 0.969, p = 0.654). E-value analysis suggested moderate robustness.

CONCLUSION

Afternoon surgery is associated with better 30-day independent ambulation, and PSD does not mediate this observational association. All findings are exploratory, hypothesis-generating, and require validation in randomized controlled trials.