Alterations in the supraspinatus muscle belly with rotator cuff tearing: Evaluation with magnetic resonance imaging.

We studied the supraspinatus muscle in patients with full-thickness rotator cuff tearing by analyzing its architecture on magnetic resonance imaging. Forty-six shoulders with rotator cuff tears requiring surgical repair were scanned parallel to the long axis of the supraspinatus muscle. We calculated the ratio of the largest width of the supraspinatus muscle belly to the distance from the greater tuberosity to the proximal end of the supraspinatus muscle. We classified the linear bands in the supraspinatus muscle, variation in its signal intensity, and irregularity and vagueness of its margins. The larger the rotator cuff tear, the more atrophic the supraspinatus muscle became. With increased atrophy, linear bands in the suprosupinotus muscle belly increased, muscle signal intensity became less uniform, and its margins became more irregular and vague.