RESUMO
OBJECTIVE: To describe infraspinatus tendon injuries with associated intramuscular edema in light of more recently elucidated anatomical knowledge. MATERIAL AND METHODS: A retrospective review was performed to identify MRI cases with infraspinatus tendon injury accompanied by muscle edema. MR images were reviewed to evaluate the location of the injury, to assess the degree of tendon retraction, and to assess for muscular changes. Clinical and surgical data were reviewed when available. RESULTS: Twenty-three patients were identified (13 males, 10 females, mean age of 52 years). MRI demonstrated infraspinatus muscle edema in all cases with variably retracted infraspinatus tendon fibers. Three patients (13 %) presented acutely after traumatic falls, 11 patients (48 %) presented after a minor trauma or recalled event, and 9 patients (39 %) presented with more chronic symptoms. Of the nine patients who underwent arthroscopic surgery, six patients (67 %) did not have an identifiable corresponding lesion, despite the findings described on the preoperative MRI. In these six cases, some superficial fibers of the transverse portion of the infraspinatus tendon remained intact on the MRI. Three patients (13 %) had follow-up MRI examinations with one progressing to severe muscle atrophy, one without progression of existing muscle atrophy, and one with no atrophy on the initial or subsequent evaluation. Eighteen of 23 patients had concomitant partial-thickness or full-thickness tears of the adjacent supraspinatus tendon. CONCLUSION: Injuries of the infraspinatus tendon with resultant muscle edema and variable muscle atrophy may, in fact, represent delaminating type injuries with differential retraction of a layered tendon and may be missed on arthroscopy.