1. Herein are described twelve instances of traumatic dislocation of the shoulder joint. Eight have been carefully studied: first in the cadaver, next by dissection, and lastly on the macerated skeletons. The other four are known only by the skeletons.
2. These twelve lesions emanate from a collection of 1826 complete skeletons of known individuals. The high percentage is probably due: first, to the class of patient who does not readily seek medical advice for a disability; and, secondly, to the relatively minor degree of disability apparently suffered by most of the twelve.
3. The classic description of the production of traumatic shoulder dislocation is not borne out by these examples.
4. In the original injury the humeral head has been forced over the glenoid margin in the region of the subscapular bursa. This is accompanied by either a stubbing fracture of the ventral glenoid margin or by a functional disability of the subscapularis muscle, or both.
5. In the subluxation or stub, the healed glenoid margin is no disability but the functional damage sustained by the subscapularis becomes the important feature. The humerus is externally rotated and is slightly eroded on its dorsal aspect adjacent to the greater tuberosity, even though the head never leaves the glenoid cavity. This condition may escape notice or be diagnosed as rheumatism.
6. Subscapularis bursitis seems to have some influence in predisposing the joint to traumatic dislocation through thinning of the glenoid margin.
7. In the true luxations the head leaves the glenoid and the final category depends upon the site of glenoid injury. If the mid-ventral margin is damaged, subcoracoid dislocation results; if the lower ventral margin is affected, subglenoid dislocation occurs. In such conditions the humeral erosion is more or less deep, depending upon extent of glenoid damage and muscular action.
8. This humeral erosion apparently continues long after the original pain and muscular spasm have given place to "rheumatism" and muscular contracture.
9. Stubbing fracture of the ventral glenoid margin, old synovitis of the subscapularis bursa, and traumatic functional deficiency in the subscapularis muscle are the three contributing causes to traumatic dislocation of the shoulder, so far as can be ascertained from our material.
10. It may be inferred that many of the cases herein described, especially those classified as stub, were cases of recurring subluxations of the shoulder joint. In view of the fact that we have definitely demonstrated the presence of bony defect, operative correction should be planned with view to correction of the subluxation by check ligaments and boneblock operations rather than by capsulorrhaphies.