In cases of rotator cuff tear, the scapulo-humeral rhythm is usually disturbed, however, the patient is able to elevate the arm to a certain extent. This paper presents an analysis of the scapulo-humeral rhythm and clarifies the function of the cuff during elevation.
Five unilateral cuff tear patients with an average age of 55 years were examined on both sides. The sizes of cuff rupture ranged from 12mm to 40mm which were confirmed at surgery. To analyze the rhythm, two roentgenograms were taken with a distance of 1 and 2 meters between the X-ray source and the film. The three landmarks of the scapula were determined and the tilting angles of the scapula in three dimensions were considered to be the medially tilting angle, downward tilting angle and upward rotation angle and they were calculated. The patient was asked to elevate both arms in the scapular plane in front of the roentgenofluoscopy (field diameter: 31cm). The movements were recorded on a video recorder and then analyzed by micro-computer.
The medial tilting angle remained almost constant at about 35 degrees during elevation, and the downward tilting angle inclined posteriorly as elevation progressed but these angles were not markedly different from those of the sound side. However, the upward rotation angle was different from that of sound side. In a patient who could elevate the arm only 30 degrees, there was only upward rotational movement of the scapula but no gleno-humeral motion. The other four patients could elevate the arm above 100 degrees, but the upward rotational movement of the scapula took the major role in the elevation compared to the sound side. These results suggest that the cuff function in stabilizing the head on the glenoid cavity is disturbed during elevation in patients with cuff tear.
