Association of interstage timing and prior surgical response with outcomes following staged bilateral total knee arthroplasty: A retrospective cohort study.

PURPOSE: Staged bilateral total knee arthroplasty (BTKA) is increasingly performed, yet the influence of inter-stage timing on complications and patient-reported outcomes (PROs) remains unclear. This study evaluated whether timing between staged BTKA procedures was independently associated with 90-day complications or failure to achieve the minimal clinically important difference (MCID) in 1-year PROs after the second surgery.

METHODS

Retrospective study of 2410 patients who underwent staged BTKA at a high-volume single institution (2014-2024). Timing was assessed using quartiles, a ≤6 versus >6-week cutoff, and as a continuous variable. The primary outcome was any 90-day complication after the second procedure, as defined by The Knee Society Guidelines. Secondary outcomes included failure to achieve MCID at 1-year for the knee injury and osteoarthritis outcome score for joint replacement (KOOS-JR) and veterans RAND 12-item survey (VRS-12) physical (PCS) and mental component scores (MCS). Multivariable regression adjusted for demographics, second-stage preoperative PROs, and complications after the first stage.

RESULTS

Median time between stages was 245 days. Timing was not independently associated with 90-day complications or failure to achieve MCID at 1-year in adjusted models. Prior complications after the first procedure (odds ratio [OR]: 4.01, 95% confidence interval [CI]: 2.21-7.26; p < 0.001) and ASA III-IV (OR: 1.60, 95% CI: 1.05-2.43; p = 0.028) were associated with increased complication risk. Failure to achieve MCID after the first surgery was strongly associated with subsequent MCID failure following the second surgery (KOOS-JR: OR: 26.34; VRS-12 PCS: OR: 31.67; MCS: OR: 8.69; all p < 0.001).

CONCLUSIONS

Inter-stage timing was not independently associated with complications or failure to achieve MCID at 1-year after adjustment for patient-level factors. Prior surgical response and ASA classification demonstrated stronger associations with postoperative outcomes following the second stage than timing alone. These findings support individualised surgical planning and shared decision-making rather than reliance on fixed interval thresholds.

LEVEL OF EVIDENCE: Level III.