Final answer:
Posterior shoulder dislocations are often caused by a force applied from the front, or a forceful internal rotation and adduction of the arm. Key structures supporting the shoulder joint include the rotator cuff muscles, glenoid labrum, ligaments, and the joint capsule.
Step-by-step explanation:
The mechanism of injury (MOI) for posterior dislocations of the shoulder typically involves a force applied from the front or a forceful contraction of the muscles that internally rotate and adduct the arm. This can happen during seizures, electric shocks or falls onto an outstretched hand. In terms of associated findings, one might observe a limited external rotation, prominence of the acromion, and fullness or bulging at the posterior aspect of the shoulder joint. The clinical presentation often includes pain and the arm held in internal rotation. Posterior dislocations can be associated with injuries to the axillary nerve or the labrum, leading to a reverse Hill-Sachs lesion.
When addressing the stability and support of the shoulder joint, structures such as the rotator cuff muscles, glenoid labrum, and the surrounding ligaments and bony anatomy play crucial roles. The rotator cuff is a group of four muscles that not only move the arm but also cinch down the humeral head into the glenoid, providing stability. The bony congruence of the glenoid fossa with the humeral head, though shallow, is deepened by the fibrocartilaginous glenoid labrum, increasing joint stability. Ligaments and the joint capsule also contribute to stability by limiting excessive movement.