Isolated lesion of the infraspinatus at the myotendinous junction: a new lesion

Purpose We have identified a previously unpublished lesion of the infraspinatus muscle at the myotendinous junction. We describe its presentation and magnetic resonance imaging (MRI) appearance, notably the absence of other tendinous pathology in the rotator cuff. Materials and methods We retrospectively reviewed 25 patients with isolated infraspinatus lesions and associated edema identified on the fat-suppressed T2-weighted images of MRI. Imaging exams and medical records collected over a 7-year period were reviewed by a team of radiologists and surgeons specializing in the shoulder. A presentation of the mechanism of injury, radiological analysis of MRI scans, and other investigations (arthro-computed tomography (CT) and electromyography studies) were carried out; all MRI included at least two fat-suppressed, T2-weighted (transverse and coronal) sequences and one T1-weighted (transverse) sequence. Results The lesion was characterized by tearing or delamination at the myotendinous junction, which was accompanied by edema of the infraspinatus muscle in the initial phase. Over time, the edema was seen to resolve and muscle atrophy, and fatty degeneration became predominant. We identified two groups by the onset of their symptoms. In the “chronic” group (44%), onset was gradual, with these patients frequently having had one or more infiltrations at presentation to us. In the “acute” group (56%), there was an initial traumatic event that was variable in intensity and mechanism. Conclusion This isolated lesion of the infraspinatus at the myotendinous junction has not been previously described. It is recognized by its characteristic MRI appearance and is not generally seen on CT arthrograms, as there is no communication with the joint. Its natural history appears to be of a progression from edema to fatty degeneration with or without myotendinous retraction and scarring. Its etiology has not yet been clearly established.