Radiologic measurement of superior displacement of the humeral head in the impingement syndrome.

A method for directly measuring the position of the humeral head on the face of the glenoid in different positions of abduction of the arm was developed. We studied three subject groups: 12 patients with normal shoulders (group 1), 15 patients with stage II impingement syndrome (group 2), and 20 patients with rotator cuff tears or stage III impingement (group 3). The study consisted of a series of anteroposterior roentgenograms in the plane of the scapula with the arm in neutral rotation. Roentgenograms were obtained at 20 degrees intervals as the arm was elevated in the plane of the scapula from 0 degree to 120 degrees. Patients held a weight equal to 2 1/2% of body weight in the hand. The parameters measured were excursion of the humeral head on the glenoid face, expressed as the distance that the center of the head lies above or below the center of the glenoid, arm angle, scapulothoracic angle, and glenohumeral angle. For patients with normal shoulders (group 1), there was no significant change in position of the humeral head with arm elevation. In contrast, those with stage II impingement (group 2) had significant (p < 0.05) superior displacement of the center of the humeral head with arm elevation. Patients with rotator cuff tears (group 3) demonstrated a significant rise (p < 0.05) during the first 40 degrees of abduction. The average position of the humeral head in the two pathologic patient groups was superior (p < 0.05) to the average head position in the normal patient group. There was no significant difference in head position between patients with stage II impingement and patients with rotator cuff tear. The ratio of the glenohumeral angle to the scapulothoracic angle during abduction was calculated for our patient groups. In both patient groups, arm abduction had a larger scapulothoracic component than for normal shoulders. The superior migration of the humeral head is a probable result of cuff failure, either partial or complete.