To assess the influence of baseline score on concordance between the Minimal Clinically Important Difference (MCID) and Patient Acceptable Symptom State (PASS) estimates obtained on persons following total knee arthroplasty (TKA).
Patients scheduled for TKA in 15 hospitals in Spain were recruited and provided pre-operative and 1-year postoperative Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) Pain and Function scores. 1 year following surgery, patients completed questionnaires that determined the importance of any changes in status since surgery as well as the extent of satisfaction with the 1-year outcome. Kappa (κ) was used to determine the extent of concordance between MCID and PASS measures for the entire sample and after splitting the sample based on quartiles of the baseline WOMAC scores.
A total of 923 patients participated in the study. The extent of concordance between MCID and PASS without regard to baseline score was κ = 0.41 (95% Confidence Interval (CI) = 0.36, 0.47) for WOMAC Function and after stratifying baseline scores into quartiles, κ = 0.72 (95%CI = 0.68, 0.77). Similar estimates were obtained for WOMAC Pain.
Baseline score has substantial influence on the extent of concordance between MCID and PASS for patients undergoing TKA. Clinicians should account for baseline score when interpreting either MCID or PASS and the extent to which these measures agree. These findings have potential to influence the interpretation of outcome following TKA.