Final answer:
The most common shoulder dislocation is the anterior dislocation, occurring from falls or impacts while the arm is extended and rotated, made possible by the glenohumeral joint's wide range of motion.
Step-by-step explanation:
The most common shoulder dislocation is the anterior dislocation, where the head of the humerus is displaced forward. This usually occurs when a person’s arm is abducted and externally rotated a position common in sports or during an impact from a fall. The structure of the shoulder joint, also known as the glenohumeral joint, permits a wide range of motion, leaving it susceptible to dislocation due to its relatively shallow socket.
To understand how the dislocation occurs, consider it usually results from a fall onto an outstretched hand or a direct blow to the shoulder area. The forces involved override the stability provided by the shoulder’s muscles and ligaments, resulting in displacement. After an anterior dislocation, the arm typically appears squared off, because the head of the humerus is no longer sitting within the glenoid cavity of the scapula.