The keeled acromion: an aggressive acromial variant--a series of 20 patients with associated rotator cuff tears.

This study describes our experience with an unusual type of acromial spur. In the last 7 years, we have treated 20 patients with a previously undescribed "keeled" acromion. The keel refers to a central, longitudinal, downward sloping spur on the acromial undersurface. Patients with a keeled acromion are at significant risk of bursal-sided as well as full-thickness rotator cuff tears. All patients in this series had significant bursal-sided tears, and 12 of 20 patients (60%) had full-thickness rotator cuff tears associated with an acromial "keel." In addition, patients with a keeled acromion are younger (average age, 52.7 years) than would be expected for patients with rotator cuff disease. Often these patients are misdiagnosed, and effective treatment is delayed. Diagnosis of a keeled acromion relies on a high level of suspicion, as well as knowledge of clinical and radiographic signs consistent with an acromial keel. We discuss the clinical presentation, radiographic findings, associated rotator cuff pathology, as well as methods to avoid intraoperative technical errors when treating patients with an acromial keel. The goal is to raise awareness of this relatively uncommon but clinically important entity and to help guide the treating surgeon's therapeutic measures.