Extensibility of the supraspinatus muscle with a rotator cuff tear evaluated by magnetic resonance imaging.

Abstract An estimate of the extensibility of the supraspinatus muscle after a rotator cuff tear is useful in selecting the most appropriate operative procedure and the prognosis after surgery. We studied the relationship between the morphological findings of the supraspinatus muscle on magnetic resonance imaging and its elongation length. Twenty-one shoulders of 20 patients with massive rotator cuff tears were scanned parallel to the long axis of the supraspinatus muscle. 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 was termed the supraspinatus muscle belly ratio. The appearance of linear bands and the degree of retraction of the tendon of the supraspinatus muscle were analyzed. The extensibility of the supraspinatus muscle decreased when the degree of retracted tendon was high, while no correlation was found with the length of the rotator cuff defect, the supraspinatus muscle belly ratio, or the appearance of linear bands.