Non-linear association between surgical duration and length of hospital stay in primary unilateral total knee arthroplasty: a secondary analysis based on a retrospective cohort study in Singapore.

Background: The relationship between surgical duration and length of hospital stay (LOS) in total knee arthroplasty (TKA) remains incompletely understood. We investigated the potential associations and modulating factors influencing LOS.

Methods: In this retrospective cohort study, we analyzed 2,394 patients undergoing primary unilateral total knee arthroplasty at Singapore General Hospital (2013-2014). Surgical duration served as the primary exposure, with LOS as the principal outcome. We employed multivariable linear regression models, including piecewise linear regression, to elucidate the relationship between surgical duration and LOS.

Results: A significant non-linear association emerged between surgical duration and LOS. A critical inflection point was identified at 115 min, beyond which LOS increased substantially (adjusted β = 0.047, 95% CI: 0.018-0.076, P = 0.0015). Stratified analyses revealed nuanced effect modifications by anemia status and American Society of Anesthesiologists Physical Status (ASA-PS) scores. Patients with moderate-to-severe anemia and higher ASA-PS scores demonstrated markedly different response patterns, with more pronounced increases in hospitalization duration.

Conclusion: Our findings demonstrate a complex, non-linear relationship between surgical duration and LOS in TKA. Anemia status and physiological reserve significantly modulate this association, suggesting the need for personalized perioperative management strategies. These insights may optimize surgical planning and resource allocation in orthopedic interventions.