BACKGROUND: Both preoperative pain sensitivity and coronal alignment philosophy may influence patient-reported outcome measures (PROMs) after total knee arthroplasty (TKA). This study investigated whether pain sensitivity predicts PROMs in robotic-assisted TKAs randomized to functional alignment (FA) or mechanical alignment (MA) and whether high pain sensitivity obscures differences between strategies.
METHODS: This was a substudy of a prospective, single-blinded randomized controlled trial. A total of 244 patients were allocated to FA (n = 123) or MA (n = 121). Pain sensitivity was assessed preoperatively using the Pain Sensitivity Questionnaire (PSQ). The Forgotten Joint Score (FJS) and Oxford Knee Score (OKS) were collected two years postoperatively. Multivariable stepwise regressions evaluated the influence of PSQ on PROMs, with adjustment for demographic and radiographic factors. Patients were stratified into high (PSQ ≥ 5.2) and low (PSQ less than 5.2) pain sensitivity groups, and FA and MA outcomes were compared. Baseline PSQ did not differ between FA and MA groups (5.7 ± 1.9 versus 5.6 ± 1.8; P = 0.58).
RESULTS: The PSQ was a negative predictor of both FJS (P = 0.02) and OKS (P < 0.01), whereas alignment strategy was not. Among low pain sensitivity patients, FA yielded a higher FJS than MA (74.9 ± 25.8 versus 61.9 ± 31.4; P = 0.03). In high pain sensitivity patients, FJS did not differ (FA 66.8 ± 25.0 versus MA 65.8 ± 29.5; P = 0.80).
CONCLUSIONS: Preoperative pain sensitivity exerted a stronger influence on PROMs than coronal alignment strategy in TKA. Alignment philosophy had no discernible effect on outcomes in patients who have high pain sensitivity, whereas patients who have low pain sensitivity showed higher FJS with FA than with MA. As these findings were derived from exploratory subgroup analyses, they should be interpreted cautiously and require confirmation in future prospective studies. Level of evidence Level I (Prospective randomized study).
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