2004 Volume 28 Issue 3 Pages 437-440
Throwing shoulder has subclinical joint laxity, but quantitative evaluation of laxity is very difficult and has not been established yet. We designed a new “shoulder positioning device” and attempted to evaluate the joint laxity of the throwing shoulder using of this device.
Bilateral shoulders of 14patients with a throwing shoulder were evaluated in this study. The average age was 21.5 years old. The subjects were seated in the device. Both scapulas were fixed on the back, and the shoulder was positioned in 90 degrees abduction with 90 degrees external rotation. A stress radiogram was filmed under a 5 kg of load on the proximal site of the humerous toward anterior and antero -inferior, and the amount of the humeral head against the glenoid were measured.
We found a significant difference between the dominant and nondominant shoulder joint in the amount of the antero-inferior humeral translation. The most significant difference was found in the direction of the anteroinferior at 60 degrees. The force given to the shoulder from the cocking phase to the acceleration phase of throwing directs toward antero-inferior, and the repetitive stress placed on the anterior capsular structure of the glenohumeral joint. Our device made the position of the arm similar to the real throwing position, and could take pictures of 2 directions. Therefore it was possible to measure the direction of the joint laxity of the throwing movement. As a result the direction of the joint laxity at the antero-inferior 60 degrees was confilm.
