Prevalence of Early Knee Osteoarthritis Illness Among Various Patient-Reported Classification Criteria After Anterior Cruciate Ligament Reconstruction

Objective: To compare the prevalence of participants meeting different patient-reported criteria for early osteoarthritis (OA) illness after anterior cruciate ligament reconstruction (ACLR). Methods: Participants completed the Knee Injury and Osteoarthritis Outcomes Score (KOOS) at a single time point 5.0–7.9 months post-ACLR. We used established KOOS subscale criteria (i.e., Luyten original and Englund original) to define patient-reported early OA illness. A two-by-two contingency table and McNemar's test were used to compare the prevalence of participants who met the Luyten original versus Englund original KOOS criteria for early OA illness. These analyses were repeated using KOOS subscale thresholds based on established population-specific patient acceptable symptom state (PASS) within the Luyten and Englund KOOS criteria (i.e., Luyten PASS and Englund PASS). Results: A greater prevalence of participants with ACLR met the Luyten original criteria (n = 165 [54%]) compared to those who met the Englund original criteria (n = 128 [42%]; χ² = 19.3, P < 0.001). When using the KOOS subscale PASS as thresholds, a significantly greater prevalence of participants with ACLR met the Luyten PASS criteria (n = 133 [43%]) compared to those who met the Englund PASS criteria (n = 85 [28%]; χ² = 48.0, P < 0.001). When combining the Luyten and Englund KOOS criteria and using the original/PASS subscale thresholds, respectively, 40%/57% of participants met neither, 24%/15% met only 1, and 36%/28% met both KOOS criteria. Conclusion: Regardless of the classification criteria used to define early OA illness, it is concerning that 28–54% of patients report considerable symptoms ~6 months post-ACLR. Our findings will improve the classification criteria to define early OA illness, which may raise awareness for the need of population-specific criteria.