Study evaluates minimal important difference for WOMAC and FJS-12 in total knee arthroplasty patients

The PROMs (Patient-reported outcome measures) help to capture the patients’ perception of the success of an intervention. The MID (minimal important difference) is a crucial characteristic of the PROMs that helps to accurately elucidate the results. A study examining MID in a TKA patient cohort depicted that MIDs can be utilized for improving the FJS-12 and the WOMAC Pain and Function scales. This can be utilized to accurately interpret meaningful differences in scores. For both scores, more advanced statistical methods were found to result in smaller MID values.

The prospective cohort study aimed to calculate the MID for the WOMAC (Western Ontario and McMaster Universities) osteoarthritis index and FJS-12 (Forgotten Joint Score-12) in a TKA patient cohort. 

Data from 199 TKA patients were collected and analyzed. The mean age was 72.3 years, 58% were females. To calculate the MID, patients were requested to complete the FJS-12, WOMAC osteoarthritis index, and transition items assessing change over time. An anchor-based methodology was employed relating score change to the response categories of the transition items utilizing both ROC (receiver operating characteristic) analysis and binary logistic regression.

Using binary logistic regression, the MID for the FJS-12, WOMAC pain score, WOMAC function score was found to be 10.8 points, 7.5 points, and 7.2 points respectively. ROC analyses illustrated a MID of 13.0 points for the FJS-12, 12.5 points for WOMAC pain and 14.7 points for WOMAC function as depicted in the following table: 

The MIDs can be used for the improvement of the FJS-12 and the WOMAC Pain and Function scores in TKA patients.