Defining Patient Acceptable Symptom State Thresholds for the IKDC Subjective Knee Form and KOOS for Patients Undergoing ACL Reconstruction

OBJECTIVES: In clinical practice and research, the magnitude of change in patient-reported outcome (PRO) is often used to assess outcome of treatment. However, a clinically meaningful change in PRO may not be associated with an acceptable state that corresponds to “feeling well”, which is also called the Patient Acceptable Symptom State (PASS). Thresholds for common PRO measures for achieving a PASS after ACL reconstruction have not been determined. The purpose of this observational cross section study was to determine thresholds for the International Knee Documentation Committee Subjective Knee Form (IKDC-SKF) and the Knee Injury and Osteoarthritis Outcome Scale (KOOS) that indicate achievement of the PASS. METHODS: Patients 1 to 5 years after primary ACL reconstruction completed a survey that included the IKDC-SKF and KOOS. Patients assessed satisfaction with their current state by answering the question “Taking into account all the activity you have during your daily life, your level of pain and also your activity limitations and participation restrictions, do you consider the current state of your knee satisfactory?” The IKDC-SKF and KOOS scores associated with a positive and negative response to this question were determined. Additionally, receiver operator characteristic (ROC) curves and the Youden Index were used to determine the PASS thresholds with the best sensitivity and specificity for each PRO that differentiated patients with an acceptable versus an unacceptable symptom state. RESULTS: One hundred and sixty seven patients (mean age, 28.8±10.9 years) completed the survey. One hundred and forty six patients indicated they were in an acceptable symptom state (PASS-Y) and 21 were not (PASS-N) (Table 1). All PROs were significantly different between the PASS-Y and PASS-N groups (p<.001). Based on ROC curve analysis, threshold values that best distinguished an acceptable versus an unacceptable symptom state, with values of sensitivity and specificity, are reported in Table 1. CONCLUSION: Patients who did not achieve a PASS have worse IKDC-SKF and KOOS scores, indicating limitations in function, sports participation, and knee-related quality of life (QoL). The differences between PASS-Y and PASS-N for the KOOS pain, symptoms and activities of daily living (ADL) subscales were smaller than differences for sports & recreation, knee-related QoL, and the IKDC-SKF. This indicates that after ACL reconstruction, achieving an acceptable symptom state is more dependent on the ability to participate in sports than on the absence of symptoms or participation in ADL. The threshold values identified will aid in determining if patients after ACL reconstruction have achieved an acceptable symptom state based on their IKDC-SKF and KOOS scores.