Importance Given the increasing importance and number of knee-related patient-reported outcome measures (PROMs), it would be desirable to have one PROM for assessing the outcomes of all patients with orthopaedic sports medicine knee conditions.
Objective The purpose of this review was to evaluate whether the existing literature supports the use and interpretation of the International Knee Documentation Committee Subjective Knee Form (IKDC-SKF) and Marx Activity Rating Scale (MARS) as the primary PROMs in the setting of orthopaedic research or clinical practice. We hypothesised that the reported data for the psychometric properties of the IKDC-SKF and MARS would meet accepted standards for interpretation and use of PROMs.
Evidence review A systematic search of MEDLINE was performed using PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines to identify articles reporting the development and psychometric properties of the IKDC-SKF and MARS. References of included articles were hand-searched to identify additional articles for inclusion. The results of these studies were extracted to determine if the reported psychometric properties for the IKDC-SKF and MARS met established standards.
Findings The reported test–retest intraclass correlations (ICCs) for the IKDC-SKF and the MARS respectively range from 0.85 to 0.99 and 0.81 to 0.97 (ICC>0.70 considered acceptable). The reported effect sizes (ES) and standardised response means (SRM) ranged from 0.76 to 2.11 for the IKDC-SKF and from 0.57 to 1.5 for the MARS (ES/SRM >0.5 or >0.8 are respectively considered moderate and large). The IKDC-SKF has been reported to show moderate/excellent correlations with 60/72 (83%) concomitantly administered measures of physical health and poor/fair correlations with 28/31 (90%) measures of mental health, thus demonstrating its convergent and divergent validity. The MARS has shown moderate/excellent correlations with 3/3 (100%) concomitantly administered measures of level of sports activities, which demonstrates its convergent validity. Standards for interpreting the IKDC-SKF, including the minimal detectable change, minimum clinically important difference, normative data and the patient acceptable symptom state, are also summarised.
Conclusions and relevance This review suggests that the IKDC-SKF and MARS have acceptable psychometric properties to support their use and interpretation to assess the clinical response of patients with a variety of knee conditions in clinical practice and research settings.