Orientation of the rotator cuff insertion facets on the humerus: comparison between individuals with intact and torn rotator cuffs.

The purpose of this work has been to compare the orientation of the rotator cuff insertions on the humerus between individuals with intact and torn rotator cuffs, respectively, to look for anatomical factors involved in the pathogenesis of rotator cuff tears. A total of 60 patients evaluated by arthro-computed tomography (CT) were divided into an intact rotator cuff group (31 patients) and a torn rotator cuff group (29 patients). The orientation angles of the lesser humeral tubercle facet and of the superior, middle and inferior facets of the greater humeral tubercle were measured in the sagittal plane between the horizontal line (defined as perpendicular to the diaphysis long axis) and the line tangent to the facet. The orientation angles of the superior and middle facets of the greater humeral tubercle were measured in the coronal plane. The comparison between the two groups showed a significant difference (p=0.009) concerning the orientation of the middle facet of the greater tubercle in the sagittal plane, with a mean angle of 36.0 degrees (S.D., 6.2 degrees) in the intact cuff group versus 31.1 degrees (S.D.,7.2 degrees) in the torn cuff group. There were no other significant differences in regard to the orientation of the facets in the sagittal and coronal planes. A decrease in the dorsal orientation of the middle facet of the greater tubercle, as we observed in the torn rotator cuff group, may reduce the inferior translatory forces generated by the infraspinatus thereby facilitating impingement of the subacromial structures. These additional anatomical data might augment the body of knowledge on rotator cuff pathology.