[Shoulder mechanism - study based on cineradiography and radiography with the arm elevated (author's transl)]

In order to better understand the shoulder mechanism and make a clinical assessment of the "zero-position", a study by means of cineradiography and radiography was performed on normal and disordered shoulders with arm elevated. The conception of the "scapular plane" has been widely accepted as the reference plane for the mechanism at the shoulder joint, but practically this plane is not easily defined. Thus, a cineradiographic study of 50 normal joints has been carried out in 7 planes between the frontal and the sagittal plane, during upward and downward movement of the arm. As a result, it was determined that the "scapular plane" should be inclined forward at an angle of 30 degrees to the frontal plane. In evaluating the anatomical relationship between the humeral head and the glenoid during upward and downward movement of the arm, 50 normal shoulders and 22 disordered shoulders composed of 12 loose shoulders and 10 rotator cuff injuries were analyzed in the "scapular plane" using devised method of measurement. Concerning the "zero-position", information was gained mostly from radiographies of 600 normal and 32 disordered shoulder joints. Especially o the disordered joints, a radiographic study of the shoulder with arm elevated was made pre- and postoperatively with the arm elevated. The results obtained are as follows, 1. In the "zero-position", the humerus must be elevated to 150 degrees in the "scapular plane", with individual variations. 2. Regularization of the glenohumeral rhythm of the normal shoulder joints was observed between the end of the "setting phase" and the "zero-position". 3. Glenohumeral mechanism of the normal and disordered shoulders was different between upward and downward movement of the arm, especially more remarkable at the disordered joints. 4. Lateral deviation of the humeral head toward the glenoid was found in the loose shoulder during upward and downward movement of the arm, especially during maximum elevation of the arm. 5. Glenoid osteotomy was determined to be the reasonable procedure for stabilizing loose shoulders, from the aspect of radiographic study with the arm elevated. 6. In rotator cuff injuries, the glenohumeral rhythm was disturbed, and in some patients instability at the glenohumeral joint was observed. From postoperative radiographic evaluation with the arm elevated, it has been observed that the anatomical situations at the glenohumeral joint have recovered to nearly norma conditions. 7. In conclusion the author emphasizes the mechanism of normal and disordered glenohumeral joints, using radiography of the shoulder with the arm elevated.