Musculotendinous infraspinatus ruptures belong to the category of “muscle strain injuries”. They differ from a classic rotator cuff tear by the following features: tendon attachment remains intact and the acute initial stage typically undergoes an intense muscular edema, replaced, 6 to 12 months later, by complete and permanent fatty infiltration of this muscle.

Between 1993 and 2007, we prospectively identified 59 musculotendinous ruptures of the infraspinatus muscle tendon complex. Fifty-eight percent of these patients were females. The average age at presentation was 50 years old. Onset was non traumatic in 78% of these cases. Twenty-nine patients were seen at the acute lesion stage with pain and, on T2 fat saturated MRI sequences, muscular edema. A second group of 30 patients presented with a stage 4 fatty infiltration of the infraspinatus muscle associated with a musculotendinous disruption. Twenty-three patients underwent EMG testing which was normal in all cases. None of these patients had a full thickness tear of the rotator cuff tendons, 21% of the patients presenting in the acute phase had a partial thickness tear of the supraspinatus, which increased to 70% in patients presenting in the chronic phase suggesting a more degenerative etiology. Calcific tendonitis was seen in 61% of patients.

Twenty-four patients underwent surgery, while the remaining 35 were treated conservatively. The average follow-up, for all of them, was 46 months (12–125). The Constant score increased from 51.7 to 69.4 (p<0.001). There was no significant difference between the operated and the non-operated groups (p=0.325). All the patients seen at the acute painful edematous stage progressed to stage 4 complete fatty infiltrations, irrespective of selected treatment. None of the patients who underwent surgery had any regression of their fatty infiltration.

Early diagnosis of this lesion can be made using T2 fat saturated MRI imaging. We hypothesize that early tendon repair which restores muscle tension in the infraspinatus may halt the progression of this entity and prevent complete functional loss of this muscle.

Level IV: Therapeutic study.