Second-Stage Knee Pain is Not Increased After Staged Bilateral Total Knee Arthroplasty: A Retrospective Linear...

Pain perception following staged bilateral total knee arthroplasty (TKA) remains controversial, with previous studies suggesting increased pain after the second knee attributed to central sensitization. This retrospective observational study aimed to compare postoperative pain between first- and second-stage TKA using a linear mixed-effects model adjusted for opioid consumption and peripheral nerve block type.

This retrospective observational study included 155 patients who underwent staged bilateral TKA under spinal anesthesia between 2015 and 2020 at Prince of Songkla University Hospital, Hat Yai, Thailand. Pain was assessed using a verbal numerical rating scale (VNRS) every 4 hours for 72 hours postoperatively. A linear mixed-effects model with a random intercept for each patient was used for the primary analysis, with last observation carried forward (LOCF) as sensitivity analysis.

Among the 155 patients included, no significant difference in pain was found between the first and second TKAs (β = -0.027; 95% CI, -0.139 to 0.085; P = 0.638). Pain decreased significantly over time (β = -0.073 per 4-hour interval; 95% CI, -0.083 to -0.063; P < 0.001). Femoral nerve block was associated with reduced pain (β = -0.321; 95% CI, -0.509 to -0.133; P = 0.001). Higher opioid consumption was associated with increased pain (β = 0.018; 95% CI, 0.014 to 0.022; P < 0.001). The LOCF sensitivity analysis confirmed no significant difference between stages (β = -0.051; 95% CI, -0.147 to 0.045; P = 0.300).

Within the first 72 hours, pain following second-stage TKA was not significantly different from that following first-stage TKA. These findings do not support central sensitization as an inevitable cause of increased second-knee pain and suggest that previously reported increases may have been confounded by uncontrolled opioid exposure. As an observational analysis, these results cannot establish causation.