A novel lesion of the infraspinatus characterized by musculotendinous disruption, edema, and late fatty infiltration.

Isolated, atraumatic rupture of the infraspinatus (IS) with associated edema of its muscle is a previously undescribed lesion. We retrospectively identified 19 patients with MRI detected, isolated lesions of the IS tendon or musculotendinous junction with associated muscle edema. The average age at the time of presentation was 47.7 years (range, 30-66). There were 15 females and 4 males. Fourteen patients were treated nonoperatively; 5 underwent an open repair. All patients underwent clinical and MRI follow-up at an average of 50.3 months (range, 24-79) after the initial MRI. Constant scores were recorded as was a detailed physical examination. Two patients had a clear history of trauma with no preceeding shoulder problems; 17 had a history of chronic shoulder pain. We identified disruption occurring within the IS tendon in 9 patients and at the level of the musculotendinous junction in 8, while the level of disruption was inconclusive in 2. No patient had other full thickness tears. Electromyographic studies were normal, as were nerve conduction velocities in the suprascapular nerve in the 15 patients tested. There was a significant improvement in the Constant score comparing the score at presentation (53 points; range, 24-69) with the score at final follow-up (67.2 points; range, 28-95; P = .009). There was no significant benefit seen comparing the gain in the Constant score between those treated operatively and nonoperatively (P = .61). All 19 patients had progressed to stage 4 fatty infiltration of the IS muscle at latest follow-up.