Convergent Validity of the Constant-Murley Outcome Measure in Patients with Rotator Cuff Disease

Abstract

Despite the popularity of the Constant-Murley score (CMS), a combined patient-report and objective (health professional administered) shoulder outcome measure, minimal information exists on its reliability or validity. The purpose of this study was to examine (1) internal consistency and convergent validity of the CMS and (2) the degree to which other shoulder measures explain variation in range of motion and strength components of the CMS. In this cross-sectional study of outcome measures, 45 patients undergoing conservative or surgical treatment for rotator cuff disease participated. Two disease-specific outcome measures, one shoulder-specific measure, and one upper extremity outcome measure were compared to the CMS. Correlations between competing measures and relative total CMS were moderate (0.56 to 0.75). The American Shoulder & Elbow Score, the Upper Extremity Functional Index, the Western Ontario Rotator Cuff Index, and the Rotator Cuff Quality of Life index explained 38%, 28%, 26%, and 10% of variance of the objective component of the CMS respectively. The patient-report component of the CMS measures a multidimensional concept. The strength component had moderate correlations with isometric strength measures of the shoulder external rotators and abductors. The total CMS appears to measure a construct that is not totally captured by competing measures. The unexplained variance may be due, in part, to the lack of importance of the patient's physical impairment to symptoms or activity limitations as measured by other instruments.