Three-dimensional relationship of the glenohumeral joint in the elevated position in shoulders with multidirectional instability.

Patients with typical atraumatic multidirectional instability often have symptoms develop, especially when the arm is elevated overhead. To clarify the pathomechanics, we analyzed the glenohumeral relationship with the arm in 135 degrees of elevation in the scapular plane using 3-dimensional reconstructed magnetic resonance imaging. We enrolled 40 normal individuals (23 men and 17 women) and 10 patients with atraumatic multidirectional instability (3 men and 7 women) in this study. The mean ages of the normal volunteers and patients were 23.4 years (range, 14-42 years) and 19.4 years (range, 15-25 years), respectively. The humeral head of normal volunteers was located on the glenoid center. In contrast, the humeral head of patients translated posteriorly from the glenoid center, even though the arm was in more extension in the anteroposterior direction. Three-dimensional computer-generated images of the static position with the arm elevated made the difference obvious between the groups and were useful for evaluating the ability to maintain the head in the glenoid center.