Dimensionality of the Knee Numeric-Entity Evaluation Score (KNEES-ACL): a condition-specific questionnaire

The benefit of anterior cruciate ligament (ACL) reconstruction has been questioned based on patient-reported outcome measures (PROMs). Valid interpretation of such results requires confirmation of the psychometric properties of the PROM. Rasch analysis is the gold standard for validation of PROMs, yet PROMs used for ACL reconstruction have not been validated using Rasch analysis. We used Rasch analysis to investigate the psychometric properties of the Knee Numeric-Entity Evaluation Score (KNEES-ACL), a newly developed PROM for patients treated for ACL deficiency. Two-hundred forty-two patients pre- and post-ACL reconstruction completed the pilot PROM. Rasch models were used to assess the psychometric properties (e.g., unidimensionality, local response dependency, and differential item functioning). Forty-one items distributed across seven unidimensional constructs measuring impairment, functional limitations, and psychosocial consequences were confirmed to fit Rasch models. Fourteen items were removed because of statistical lack of fit and inadequate face validity. Local response dependency and differential item functioning were identified and adjusted. The KNEES-ACL is the first Rasch-validated condition-specific PROM constructed for patients with ACL deficiency and patients with ACL reconstruction. Thus, this instrument can be used for within- and between-group comparisons.