Tendon retraction with rotator cuff tear causes a decrease in cross-sectional area of the supraspinatus muscle on magnetic resonance imaging

Background: Muscle atrophy and fatty degeneration of the rotator cuff muscles have been reported as negative prognostic indicators after rotator cuff repair. Although the Y-shaped view is widely used for measuring the cross-sectional area of the supraspinatus muscle, the contribution of retraction of the torn tendon as well as muscle atrophy must be considered. The purpose of this study was to clarify the relationship between cross-sectional area and tendon retraction or size of the tear. Methods: This study included 76 shoulders that were evaluated arthroscopically for the presence and size of tears. Cross-sectional areas of rotator cuff muscles were measured from the Y-shaped view to 3 more medial slices. The occupation ratio and tangent sign were evaluated on the Y-shaped view. The retraction of torn tendon was also measured on the oblique coronal images. Results: On the Y-shaped view, the cross-sectional area of the supraspinatus and the occupation ratio decreased in conjunction with the increase in tear size. A significant decrease in cross-sectional area was noted only in large and massive tears on more medial slices from the Y-shaped view. Significant decreases in the cross-sectional area of the infraspinatus were observed in large and massive tears on all images. A negative correlation was found between tendon retraction and cross-sectional area, which was strongest on the Y-shaped view. Conclusions: To avoid the influence of retraction of the supraspinatus tendon, sufficient medial slices from the musculotendinous junction should be used for evaluation of muscle atrophy. (C) 2016 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.