Reliable Internal Consistency and Adequate Validity of the Forgotten Joint Score-12 after Primary Anterior Cruciate Ligament Repair

PURPOSE: To validate the Forgotten Joint Score-12 (FJS-12) as a subjective outcome metric for patients undergoing arthroscopic primary anterior cruciate ligament (ACL) repair. METHODS: In this retrospective study, all patients undergoing primary ACL repair for complete isolated proximal tears between 2008 and 2018 were eligible for inclusion. Patients were contacted and asked to complete the FJS-12, Lysholm Knee Score, modified Cincinnati score, Single Assessment Numeric Evaluation (SANE), Subjective International Knee Documentation Committee (IKDC), and Anterior Cruciate Ligament Return to Sport after Injury (ACL-RSI) scale at a minimum of 1 year of follow-up. Internal consistency, convergent validity, and ceiling effects were analyzed. RESULTS: Ninety-six patients could be included (62%), with a mean FJS-12 score of 86.9 ± 14.0 (range, 31.3-100). The FJS-12 showed reliable internal consistency (Cronbach’s alpha = 0.89). Construct validity was moderate to strong (r = 0. 621-0.702). Ceiling effect for the FJS-12 was 21.9%, which was lower than for the Lysholm (44.6%), modified Cincinnati (45.1%), equal to the IKDC subjective (21.9%), and SANE score (22.0%) but higher compared to the ACL-RSI (12.8%). Furthermore, internal consistency for the other scores was also good to excellent (range Cronbach’s alpha = 0.627-0.953). CONCLUSION: The FJS-12 shows high internal consistency and construct validity after primary ACL repair. Furthermore, this metric showed equal or less ceiling effect than most other scores, although still notable. This study suggests that the FJS-12 is an easy and validated outcome metric to evaluate subjective primary repair outcomes. LEVEL OF EVIDENCE: Level III, diagnostic study.