To describe the ceiling effect for the components of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score and identify preoperative independent predictors for patients who achieve maximal scores (ceiling effect) after total knee arthroplasty (TKA).
A retrospective cohort of 2589 patients undergoing a primary TKA were identified from an established arthroplasty database. Patient demographics, WOMAC and Short Form 12 (SF-12) scores were collected preoperatively and 1 year postoperatively. Logistic regression analysis was used to identify independent preoperative predictors of patients achieving ceiling scores.
The ceiling effect was 26.8% (n = 695) for the pain score, 6.4% (n = 165) for the function score, and 21.2% (n = 548) for the stiffness score. Lower body mass index (P = .001), absence of gastric ulceration (P = .04), absence of anemia (P = .02), absence of depression (P = .004), and absence of back pain (P < .001) and better preoperative WOMAC pain and SF-12 physical (P = .01) and mental (P < .001) scores were associated with a ceiling WOMAC pain score. Male gender (P = .03), lower body mass index (P = .040), absence of gastric ulceration (P = .004), and absence of back pain (P < .001) and better preoperative SF-12 physical (P = .02) scores were associated with a ceiling WOMAC function score. Male gender (P = .001), absence of back pain (P < .001), and better preoperative WOMAC stiffness score (P = .005) and SF-12 mental (P = .001) scores were associated with a ceiling WOMAC stiffness score.
The WOMAC pain and stiffness components demonstrated a high ceiling effect but in contrast the functional score had a low ceiling effect. The absence of back pain was a common predictive factor for all 3 components and had the greatest impact upon the likelihood of achieving a ceiling score.