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Infraspinatus Muscle Atrophy: Implications?¹

¹ From the Department of Radiology, National Institutes of Health, Bldg 10, Rm 1C640, 10 Center Dr, Bethesda, MD 20892-1182 (L.Y.); and Department of Radiology, Georgetown University Medical Center, Washington, DC (U.M.). Received November 13, 2001; revision requested January 28, 2002; final revision received April 30; accepted May 14. Address correspondence to L.Y. (e-mail: yaolawrence@yahoo.com).

PURPOSE: To evaluate associated findings in patients who exhibited atrophy of infraspinatus muscle at magnetic resonance (MR) examination of their shoulders to clarify implications of this abnormality.

MATERIALS AND METHODS: With an electronic database search, cases of advanced infraspinatus muscle atrophy in patients who underwent MR imaging during a 1-year period for evaluation of shoulder pain or dysfunction were identified. The analysis was restricted to cases interpreted by one reader who applied a standardized method of reporting. Associated MR imaging findings in these cases were tabulated.

RESULTS: Advanced infraspinatus muscle atrophy was encountered in 51 (4.3%) of 1,191 MR examinations of the shoulder. Tears of the infraspinatus tendon were present in only 27 (53%) of 51 cases. In 46 (90%) of 51 cases, a full-thickness tear was present in the anterior portion of the rotator cuff. In 10 (20%) of 51 cases with infraspinatus muscle atrophy, cuff muscle atrophy was confined to the infraspinatus muscle. Cuff muscle atrophy was isolated to the infraspinatus muscle in four (17%) of 24 cases in which atrophy of the infraspinatus muscle was present despite an intact tendon. In none of the 51 cases was there a mass in the suprascapular or sphenoglenoid notch.

CONCLUSION: Infraspinatus muscle atrophy typically occurs with tendon tears in the anterior aspect of the rotator cuff. Concomitant atrophy in the supraspinatus muscle often is present, but infraspinatus muscle atrophy can occur in isolation, and this finding does not imply that the infraspinatus tendon is ruptured.

© RSNA, 2002

Index terms: Muscles, injuries, 41.4813 • Muscles, MR, 41.121411, 41.121412, 41.121413, 41.4813 • Shoulder, injuries, 41.4813 • Shoulder, MR, 41.121411, 41.121412, 41.121413, 41.4813

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