Construct Validity and Test Re-Test Reliability of the Forgotten Joint Score

Consecutive patients undergoing knee arthroplasty completed questionnaires: FJS, Knee Injury and Osteoarthritis Outcome Score (KOOS) and WOMAC Score (mean 39 months after surgery), and were mailed a repeat questionnaire after 4 to 6 weeks. The test–retest reliability was almost perfect for the FJS (ICC = 0.97), and the FJS subdomains (ICC > 0.8). Convergent construct validity of the FJS was correlated with the KOOS Subscores of Quality of Life (0.63, P = 0.001), Symptom (0.33, P = 0.001), Pain (0.68, P = 0.001) and ADL (0.66, P = 0.001) and the Total WOMAC (0.70, P = 0.001). The FJS demonstrates high test–retest reliability and construct validity compared to the Normalised WOMAC and KOOS Subscales. The FJS does not demonstrate the ceiling effect of the WOMAC or KOOS pain scores so may have greater discriminatory ability following TKR.