Impact of psychological distress on pain and function following knee arthroplasty.

BACKGROUND Preoperative psychological distress has been reported to be an important risk factor for poor outcome following lower-extremity arthroplasty. We determined the independent impact of preoperative psychological distress on three, twelve, and twenty-four-month WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) pain and function scores and on change scores over those time periods. METHODS Data were obtained from an international group of 952 patients in thirteen centers participating in the Kinemax Outcomes Study. Patients completed the WOMAC and Short Form-36 (SF-36) questionnaires. The mental health (MH) scale of the SF-36 was used to quantify the impact of psychological distress on WOMAC pain and function scores. We also dichotomized patients into groups with and without psychological distress on the basis of evidence-based cut-points. Repeated-measures models were used to derive mean preoperative and three, twelve, and twenty-four-month WOMAC pain and function scores and general linear models were used to derive change scores for patients with and without psychological distress after adjustment for covariates. RESULTS Psychological distress, when examined on a continuous scale, was found to predict pain and function at all time-points. WOMAC pain scores for psychologically distressed patients were 3 to 5 points lower, depending on the time-frame, than the scores for the non-distressed patients, after adjustment for covariates. WOMAC function scores did not differ significantly between the two groups following surgery. The changes in the WOMAC pain and function scores for the psychologically distressed patients were not significantly different from those for the non-distressed patients. CONCLUSIONS Many patients with psychological distress demonstrate a substantial decrease in that distress following surgery. Patients who are distressed have slightly worse pain preoperatively and for up to two years following knee arthroplasty as compared with patients with no psychological distress. With the exception of preoperative scores, these differences are not likely to be measurable at the individual patient level. WOMAC pain and function change scores do not differ between patients with and without distress after adjustment for covariates. LEVEL OF EVIDENCE Prognostic Level I.