Background: Normative data are essential to the evaluation of shoulder function. The purposes of this study were to establish a normative database of isometric shoulder strength measured in asymptomatic individuals verified to have intact rotator cuffs and to determine the effect of asymptomatic rotator cuff tears on shoulder strength.
Methods: Two hundred and thirty-seven volunteers with no shoulder pain or history of shoulder injury were screened with ultrasonography bilaterally for rotator cuff tears and then underwent isometric strength measurements for abduction in the scapular plane and external rotation. Statistical analysis was performed to evaluate the effect of age, body habitus, hand dominance, and the presence of a rotator cuff tear on shoulder strength.
Results: Of the 237 volunteers, forty-one were found to have a torn rotator cuff in at least one shoulder. The prevalence of rotator cuff tears was 0% for the subjects between forty and forty-nine years old; 10%, between fifty and fifty-nine years old; 20%, between sixty and sixty-nine years old; and 40.7% for those seventy years old or older. Both abduction strength and external rotation strength in the male subjects showed an age-dependent decrease, whereas only abduction strength showed an age-dependent decrease in the female subjects. In multiple regression analysis, age and weight were the most important predictors of abduction strength and external rotation strength, respectively. In the shoulders with a large-to-massive full-thickness rotator cuff tear, abduction strength was significantly decreased (p = 0.007). Additionally, the ratio of abduction strength to external rotation strength was significantly decreased in the shoulders with a large-to-massive full-thickness tear compared with the shoulders with an intact rotator cuff (p < 0.001).
Conclusions: There is a high prevalence of rotator cuff tears in elderly asymptomatic individuals. Asymptomatic shoulders with a large-to-massive full-thickness rotator cuff tear have significantly decreased abduction strength. When there is a substantial decrease in abduction strength in relation to external rotation strength, the presence of an asymptomatic full-thickness tear should be suspected in that shoulder. Previous studies establishing normative values for isometric shoulder strength may have been skewed by the presence of asymptomatic rotator cuff tears in elderly subgroups.
Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from the National Institutes of Health (R01 AR051026-01A1). Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
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Investigation performed at the Department of Orthopaedic Surgery, Barnes-Jewish Hospital, Washington University School of Medicine, St. Louis, Missouri
- Copyright © 2009 by The Journal of Bone and Joint Surgery, Incorporated
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