Radiographic analysis of the acromion in the loose shoulder.

To investigate the contribution of bony stability to the pathogenesis of the loose shoulder, geometric parameters of the acromion by use of cineradiography were evaluated in patients with a loose shoulder and compared with those in the normal shoulder. One hundred twenty healthy individuals and eighty-two patients were enrolled. To evaluate the size of the acromion and the coverage of the humeral head by the acromion, the anterior width of the acromion and three angle parameters were measured. The findings demonstrated that the loose shoulder had a relatively smaller and more upwardly inclined acromion that was against the glenoid and provided less coverage of the humeral head. These characteristics of the acromion may contribute to the hypermobility and functional instability of the shoulder joint observed in patients with a loose shoulder. Therefore, a radiographic evaluation of the geometry of the acromion is important to determine the pathogenesis of the loose shoulder.