Coverage of the humeral head by the coracoacromial arch: relationship with rotator cuff tears

The pathogenetic roles of the coracoacromial arch in the development of rotator cuff tears are still controversial. This study compared the anteroposterior coverage of the humeral head by the coracoacromial arch between shoulders with and without full-thickness rotator cuff tears. Forty-two shoulders from 21 embalmed cadaveric specimens were macroscopically examined. Specimens were divided into 2 groups:shoulders with full-thickness cuff tears (tear group) and those with intact cuff tendons (normal group). The coverage angle of each component of the coracoacromial arch was measured using true lateral photographs. We also measured the angle of the total arc of the coracoacromial arch, as well as the angle of the anterior acromial projection. These data were compared between the tear group and the normal group. Although no significant differences were observed in the total arc of the coracoacromial arch between the groups, the tear group had significantly less coverage by the coracoacromial ligament than did the normal group (p＜0.05). Moreover, greater anterior acromial projection was observed in the tear group (p＜0.05). These results suggest that greater coverage of the bony structures on the rotator cuff may correlate with the development of rotator cuff tears.