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

Patient-related outcome measures (PROMs) are commonly used to gauge treatment effects in patients with anterior cruciate ligament (ACL) deficiency. Valid measures of specific conditions depend on relevant item content. While item content can be derived either from clinicians (face validity) or from patients, item relevance and comprehensiveness can only be confirmed by the patient (content validity). Focus group and single interviews were conducted with patients' pre- and post-ACL reconstruction in order to construct a condition-specific PROM for the target patients. One hundred fifty-seven items from a previously conducted literature search were used as a basis for content genesis. Content saturation was achieved after three focus groups and seven single interviews. Thirty-eight items from the literature search were directly endorsed, and five modified items were endorsed. Twelve new item themes with verbatim content emerged. Thus, a 55-item pilot PROM consisting of six conceptual domains was assembled. We have constructed a condition-specific PROM for measurement of surgical and non-surgical treatment effects on ACL deficiency. The instrument possesses face and content validity. A pilot survey to assess the psychometric properties will be performed using Rasch measurement theory.