Jeffrey D. Placzek

Background: Several shoulder function scores are used in research, with no universally adopted standard. This study compares 6 shoulder outcome scales. Hypothesis: Correlations exist between shoulder outcome scales, allowing conversion between scales. Shoulder scales are correlated with age. Study Design: Regression and correlation study. Methods: Seventy subjects with shoulder pain completed 6 shoulder outcome scales. Pearson correlations were calculated between the total scores of the 6 instruments, between the components of the scales, and with age. Regression equations were calculated between scales. Results: The range of r values for total scores was 0.495 [.lessequal] r [.lessequal] 0.770, P [.lessequal] .01. In general, a scale's components were themselves highly correlated and added little new information to the scale (0.260 [.lessequal] r [.lessequal] 0.705, P [.lessequal] .05). Most of the scale scores were highly correlated with age (0.291 [.lessequal] r [.lessequal] 0.582, P [.lessequal] .05). Constant's reported corrections for age reduced (from r = -0.582 to r = -0.250, P < .05) but did not eliminate age as a confounding variable. Conclusions: Correlations exist between shoulder outcome scales, but existing shoulder scales are not equivalent in their assessments of function; they contain redundant information and, in some cases, may reflect a patient's age better than his/her shoulder function. The utility of conversion equations is minimized as a result of low to moderate correlations between scales.

Introduction: Shoulder strength is an integral component of shoulder function. In assessing shoulder function many functional scales rely on direct or indirect measures of strength. Strength, and thus these scales, is often highly correlated with age. We propose an allometric method for assessing shoulder strength. Allometric modeling has provided accurate predictions of biologic growth and physiologic function in both human and animal studies. Allometry utilizes the relationship between the two homologous structures on the left and right sides of the body, providing in effect an internal control and thus eliminating many confounding effects, e.g. age and level of activity.Methods: Twenty patients with unilateral shoulder dysfunction underwent strength testing of their affected and unaffected shoulder. Strength testing of the bilateral shoulders was also assessed in twenty people without shoulder pain in order to delineate the effect of hand dominance on strength in those without shoulder pain. Absolute and predicted strength deficits of the involved shoulder were calculated via regression analysis. Pearson's correlation coefficients were computed between age and strength.Results: Utilizing the contralateral extremity as an internal control eliminates age as a confounding variable in predicting strength outcomes (r = 0.093).Conclusion: Allometric concepts, applied to shoulder strength assessment, eliminates age as a confounding variable. Strength testing of both shoulders should be considered in the development of future shoulder outcome scales in order to eliminate the strong influence of age. © 2003 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.