Injuries of Upper Limb
In an uncomplicated dislocation of the glenohumeral joint, the humeral head usually dislocates primarily in which of the following directions?
a. The glenohumeral joint is bounded posteriorly by the teres minor and infraspinatus muscles and partially by the long head of the triceps.
b. It is bounded laterally by the powerful deltoid muscle; superiorly, the acromion process precludes upward dislocation.
c. However, anteriorly and inferiorly the pectoralis major and the long head of the biceps do not completely stabilize the glenohumeral joint; in this region the articular ligaments and joint capsule provide the major structural support.
d. Thus, the joint is not strongly supported in its anteroinferior aspect, and consequently anterior (or anteroinferior) dislocations are the most common glenohumeral dislocations.
e. The humeral head is driven anteriorly, which tears the shoulder capsule, detaches the labrum from the glenoid, and produces a compression fracture of the humeral head.
f. Most glenohumeral dislocations result from a posteriorly directed force on an arm that is partially abducted. Posterior dislocation is much rarer and should raise the possibility of a seizure as the precipitating cause.