Final answer:
The question discusses Posterior Shoulder Dislocation, an injury of the shoulder joint where the head of the humerus is backwardly displaced, typically due to trauma when the arm is abducted. It involves the glenohumeral joint which allows extensive movements, and when dislocated, can lead to various complications including 'frozen shoulder'.
Step-by-step explanation:
The question pertains to a Posterior Shoulder Dislocation, a type of injury where the head of the humerus is displaced backwardly, often presenting as internally rotated, resembling the silhouette of a lightbulb on an X-ray image. This type of dislocation is less common than anterior dislocations due to the strength of the supporting muscles and ligaments around the anterior, superior, and posterior aspects of the humerus, which typically lead to dislocations in an inferior direction. The glenohumeral joint, at the articulation between the glenoid cavity of the scapula and head of the humerus, allows for a wide range of movements including flexion/extension, abduction/adduction, circumduction, and medial/lateral rotation. Posterior humeral dislocations can be a result of traumatic forces applied to the humerus when the arm is fully abducted, leading to injuries such as a tear in the glenoid labrum or rotator cuff, inflammation, formation of scar tissue, or adhesive capsulitis ("frozen shoulder"). The scapula and clavicle work together to provide stability for shoulder movements, and any injury to the shoulder joint requires careful examination of these articulations and the muscle attachments associated with them.