The Reliability of the Constant–Murley Shoulder Scoring System

Abstract

Background The Constant–Murley score (CMS) is a widely used scoring system. However, its objective component is open to inter-rater variability. The present study aimed to assess the inter-rater reliability of the objective component of the CMS. Methods Fifteen clinicians of varying experience were given 18 standardized photographs of 10 normal subjects of varying age and build, equating to 24 fixed shoulder positions. Each rater visually estimated the angle of each shoulder and repeated the process at 1 week using a goniometer. These angles were converted to their appropriate CMS. The intraclass correlation coefficient (ICC) was calculated using SPSS (SPSS Inc., Chicago, IL, USA) to assess inter-rater reliability. Results The mean postgraduate experience of our raters was 7.13 years. There were a total of 360 CMS estimated visually. The inter-rater ICC was 0.909 [95% confidence interval (CI) 0.854 to 0.952]. The goniometer-based CMS were similar: ICC 0.950 (95% CI 0.907 to 0.976) (Cronbach's alpha = 0.993). Comparing CM scores between visual estimation and goniometry demonstrated an inter-rater ICC of 0.409 (95% CI–0.0301 to 0.827). Discussion To our knowledge, this is the first attempt to define the reliability of the objective component of the CMS using large numbers of observers and patients. We have shown that the CMS is highly reliable between raters providing that the same method is used. In the present study, visual estimation was found to be as reliable between raters as the goniometer. However, the reliability of the score is dramatically affected if the two methods are interchanged between raters.