Forgotten Joint Score Thresholds for Forgotten Joint Status and Patient Satisfaction after Unicompartmental Knee Arthroplasty in Chinese Patients

The Patient Acceptable Symptom State (PASS) and “forgotten joint” represent 2 treatment goals that arthroplasty surgeons often pursue. However, the actual Forgotten Joint Score (FJS-12) that corresponds to the PASS and forgotten joint in unicompartmental knee arthroplasty (UKA) patients remains unknown.

One hundred ninety-three patients who underwent a medial UKA for knee osteoarthritis with a minimum of 1-year follow-up were included. Patients were asked to complete the FJS-12 and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaires. We used patient-reported satisfaction and the Patient’s Joint Perception questions as anchors to determine the achievement of PASS and the forgotten joint, respectively. FJS-12 thresholds for PASS and the forgotten joint were calculated using the anchor-based receiver operating characteristic curve analysis. The ability of the FJS-12 and WOMAC scores to detect the PASS and forgotten joint was compared with DeLong’s test.

Based on the answers to the anchor questions, 176 (91.2%) of the 193 total patients achieved the PASS and 34 (17.6%) patients achieved a forgotten joint after UKA. The FJS-12 outperformed the WOMAC with respect to detecting a forgotten joint ( P = .008), but they performed equally well in terms of detecting PASS ( P = .950). The FJS-12 threshold for PASS was 40.63 (sensitivity: 84.1%, specificity: 76.5%) and for the forgotten joint was 84.38 (sensitivity: 97.1%, specificity: 88.1%).

For UKA patients, the FJS-12 score has a superior ability to detect a forgotten joint when compared to the WOMAC. The FJS-12 threshold for the PASS is 40.63, while a score above 84.38 can be interpreted as having achieved a forgotten joint.