Determining Maximal Outcome Improvement Thresholds for Patient-Reported Outcome Measures After Primary ACL Reconstruction: A Mid-Term Follow-up Study Using the Anchor Method

Background: The clinical interpretation of patient-reported outcome measures (PROMs) after anterior cruciate ligament (ACL) reconstruction (ACLR) can be challenging. This study aimed to establish the clinical relevance of PROMs by determining maximal outcome improvement (MOI) thresholds at mid-term follow-up after primary ACLR.

Methods: A total of 343 patients who underwent primary single-bundle ACLR using hamstring tendon autograft at our institute were included. Patients were queried with a 2-option anchor question regarding satisfaction with their current knee symptom state. The MOI of a PROM was calculated for each patient as the percentage of improvement normalized by the maximal possible improvement. The MOI threshold for each PROM was determined as the optimal cutoff value for predicting patient satisfaction based on receiver operating characteristic curve analysis. Multivariable logistic regression analyses were performed to identify predictors of achieving these thresholds. Subgroup analyses that stratified the time from injury to surgery within the cohort were performed, and MOI thresholds were recalculated within each of these subgroups. The PROMs evaluated in this study were the modified Lysholm Knee Score and the International Knee Documentation Committee Subjective Knee Evaluation Form (IKDC) score.

Results: The calculated MOI threshold was 35.1% for the Lysholm score and 46.7% for the IKDC score. A longer time from injury to surgery reduced the odds of achieving the MOI threshold for the Lysholm score (odds ratio [OR] per time bracket = 0.7114, p < 0.0001) and IKDC score (OR = 0.8038, p = 0.0003). Male sex was associated with higher odds of achieving the MOI threshold for the IKDC score (OR = 1.9645, p = 0.0143). For patients with chronicity of ≤6 months, the MOI threshold was 35.1% for the Lysholm score and 57.9% for the IKDC score, and for patients with chronicity of >6 months, the thresholds were 24.5% and 27.1%, respectively.

Conclusions: The calculated MOI thresholds for the Lysholm and IKDC scores at mid-term follow-up after primary ACLR were 35.1% and 46.7%, respectively. Greater chronicity of the ACL injury was associated with lower odds of achieving the MOI thresholds for the PROMs at mid-term follow-up.

Level of evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.