Patient Acceptable Symptom State Thresholds for IKDC-SKF and KOOS at the 10-Year Follow-up After Anterior Cruciate Ligament Injury: A Study From the Delaware-Oslo ACL Cohort

Abstract

Background: Clinicians need thresholds for the Patient Acceptable Symptom State (PASS) and Treatment Failure to interpret group-based patient-reported outcome measures after anterior cruciate ligament (ACL) injury. Validated thresholds that are crucial for accurately discerning patient symptom state and facilitating effective interpretation have not been determined for long-term follow-up after ACL injury. Purpose: To calculate and validate thresholds for PASS and Treatment Failure for the International Knee Documentation Committee Subjective Knee Form (IKDC-SKF) and the Knee injury and Osteoarthritis Outcome Score (KOOS) subscales at the 10-year follow-up after ACL injury. Study Design: Cohort study; Level of evidence, 3. Methods: A total of 163 participants with unilateral ACL injury (treated with reconstruction or rehabilitation alone) from the Delaware-Oslo ACL Cohort were included. Thresholds for PASS were calculated for IKDC-SKF and KOOS subscales using anchor-based predictive modeling and receiver operating characteristic (ROC) analysis. Too few participants had self-reported Treatment Failure to calculate thresholds for that outcome. Nonparametric bootstrapping was used to derive 95% CIs. The criterion validity of the predictive modeling and ROC-derived thresholds were assessed by comparing actual patient-reported PASS outcome with the calculated PASS outcome for each method of calculation and calculating their positive and negative predictive values with respect to the anchor questions. Results: A total of 127 (78%) participants reported satisfactory symptom state. Predictive modeling PASS thresholds (95% CIs) were 76.2 points (72.1-79.4 points) for IKDC-SKF, 85.4 points (80.9-89.2 points) for KOOS Pain, 76.5 points (67.8-84.7 points) for KOOS Symptoms, 93.8 points (90.1-96.9 points) for KOOS activities of daily living, 71.6 points (63.4-77.7 points) for KOOS Sports, and 59.0 points (53.7-63.9 points) for KOOS quality of life (QoL). Predictive modeling thresholds classified 81% to 93% of the participants as having satisfactory symptom state, whereas ROC-derived thresholds classified >50% as unsatisfied. The thresholds for IKDC-SKF, KOOS Sports, and KOOS QoL resulted in the most accurate percentages of PASS among all identified thresholds and therefore demonstrate the highest validity. Conclusion: Predictive modeling provided valid PASS thresholds for IKDC-SKF and KOOS at the 10-year follow-up after ACL injury. The thresholds for IKDC-SKF, KOOS Sports, and KOOS QoL should be used when determining satisfactory outcomes. ROC-derived thresholds result in substantial misclassification rates of the participants who reported satisfactory symptom state.