Minimal Clinically Important Differences for Patient-Reported Outcomes After TKA Depend on Central Sensitization

Background: To our knowledge, it is still unknown if central sensitization (CS) influences the magnitude of the minimal clinically important difference (MCID) for patient-reported outcome measures after total knee arthroplasty (TKA). The purpose of this study was to determine the influence of CS on the MCID for the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score in patients who underwent TKA for knee osteoarthritis.

Methods: A total of 422 patients who underwent unilateral TKA and completed a 2-year follow-up were enrolled in this study. CS was measured using the Central Sensitization Inventory (CSI). The WOMAC score was used to evaluate preoperative and postoperative patient-reported outcomes. The measurement of the MCID was performed separately for patients with and without CS using both the anchor-based method and the distribution method. The change difference method defined the MCID as the difference in preoperative-to-postoperative change between the minimal-improvement group and the no-change group. In addition, the MCID was calculated using receiver operating characteristic (ROC) curve analysis. The percentage of MCID achievement in each group was also compared.

Results: According to the change difference method, the MCID for the WOMAC total score was 23.4 points for patients with CS and 14.7 points for patients without CS. The MCID using the ROC cutoff value for the WOMAC total score was 29.5 points for the patients with CS and 26.5 points for the patients without CS. MCID achievement rates in WOMAC pain, function, and total scores were all found to be significantly higher in the patients without CS through the change difference method and the ROC method (all p < 0.05).

Conclusions: The MCID for the WOMAC score of patients with CS after TKA was greater than that for patients without CS. Furthermore, by applying the calculated MCID to the group to which the patients belonged (with or without CS), we determined that patients with CS showed a lower MCID achievement rate than patients without CS.

Level of Evidence: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.