Normal and abnormal motion of the shoulder

TLDR

The study measured roentgenographic parameters of shoulder motion—including scapular movement, arm angle, glenohumeral and scapulothoracic angles, humeral head excursion, and instant center of motion—in twelve normal subjects and fifteen patients. Scapular external rotation with abduction, a glenohumeral‑to‑scapulothoracic movement ratio of 5:4 after about 30°, and a center of rotation within six millimeters of the humeral ball’s geometric center were observed, with abnormal values associated with pain and prior injury, indicating diagnostic potential.

Abstract

The roentgenographic parameters of motion in normal and abnormal shoulders, including the movement of the scapula, arm angle, glenohumeral angle, scapulothoracic angle, excursion of the humeral head, and instant center of motion for abduction in the plane of the scapula, were determined in twelve normal subjects and fifteen patients. The scapula rotated externally with abduction. The ratio of glenohumeral to scapulothoracic movement was 5:4 after about 30 degrees of abduction. The center of rotation of the glenohumeral joint for abduction in the plane of the scapula was located within six millimeters of the geometric center of the humeral ball. The average excursion of the humeral ball on the face of the glenoid in the superoinferior plane between each 30-degree arc of motion was less than 1.5 millimeters in normal subjects. Significant previous injury resulting in abnormal mechanics of the shoulder joint was associated with abnormal values for excursion of the instant center and of the humeral head. An abnormal glenohumeral-to-scapulothoracic ratio was associated with significant pain in the shoulder. The fact that these various parameters were sensitive indicators of normal and abnormal motion raises the possibility of diagnostic clinical application.