Normalization of the Constant Score
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The Constant score is a widely used shoulder-specific scoring system. In 1992 the European Shoulder and Elbow Society mandated the use of the Constant score in all peer-reviewed papers, making it the most widely used shoulder evaluation instrument in Europe. First described by Constant and Murley in 1986, it proposes a scoring system directed exclusively toward a numeric description of the quality of function of the shoulder. Instead of relying on tests of specific functional movements (eg, brushing one’s hair, removing an object from a shelf, and throwing a ball), it uses subjective and objective measures to determine whether a certain functional movement is possible (eg, forward elevation, external rotation, and internal rotation of the shoulder). It is separated conceptually from the diagnosis of the shoulder, thereby making it applicable regardless of diagnosis. As an outcomes tool, the Constant score includes an analysis of pain, shoulder motion, strength, and function. From a perfect score of 100, it reserves 35 points for patient-reported subjective assessment, including the presence of pain and the ability to perform basic activities of daily living, and 65 points for objective measurement. For the latter, 40 points are allocated to range of motion and 25 points are allocated to strength. The relative weight of subjective and objective findings is based on statistical analysis correlating subjectively perceived disability with the results of a combined objective and subjective evaluation.
Because the strength of the normal shoulder may differ by gender and deteriorate with age, the Constant score will also decrease, although the score may still be normal for the patient’s age and gender. To account for age-and gender-related differences, normal results for this scale must be determined across a large population of patients without shoulder disease. Unfortunately, to date, there are no peer-reviewed, large population studies to provide normalization data for the Constant score despite the fact that numerous publications suggest they are using an adjusted or normalized score.
A careful distinction in terminology must be made between validation and normalization. The former seeks not only to determine test-retest reliability of an outcomes measure but also to assess the correlation between a variety of outcomes instruments. The latter seeks to provide a standard, derived from a large population of individuals without joint-specific com- plaints, against which measurements are compared and adjusted. The purpose of this investigation is to normalize the results of the Constant score based on age and gender in patients without shoulder symptoms.
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