Purpose
The purpose of this study was to investigate the glenohumeral movement in throwing motion by using cineradiography, particularly from the cocked up phase to the ball release phase in the horizontal plane.
Materials and Methods
The subjects were 48 shoulders in 48 baseball players who had throwing pain relieved by distension arthrography and 35 healthy shoulders in 42 volunteers. In the sitting position, they went through the throwing motion from the cocked up phase to the follow-through phase and usually finished the whole throwing phase in 6 seconds. The axial view of the glenohumeral joint during the whole phase of throwing was observed with the aid of an image intensifier and recorded on a video tape. The motion was analysed with an image analyzing system. From the records obtained, images were reviewed at every 10 degrees between 40 degrees and 150 degrees by measuring the glenohumeral angle. A coordinate axis was determined and the center of the humeral head was obtained.
Results
The center of the humeral head moved posterior to the line bisecting the width of the glenoid and tended to translate its position concentrically at the phase of abduction in the horizontal plane and moves its position eccentrically from 20 degrees of adduction in normal shoulders. In pathological shoulders on the other hand, the anterior translation occurred in both adduction and abduction and significant eccentric translations were also observed from 30 degrees of adduction to 60 degrees of abduction in the horizontal plane.
Conclusion
Throwing motion disorders of the shoulder are associated with anterior and eccentric shifts of the humeral head.
