The most mobile joint in the body that allows the arm to move in many directions is the shoulder joint. This ability to move makes the shoulder joint inherently unstable and the most often dislocated joint in the body.
The head of the humerus or the upper arm bone sits in the glenoid fossa, which is an extension of the scapula, or shoulder blade. There is a need to maintain stability because the glenoid fossa is so shallow, other structures within and surrounding the shoulder joint.
Within the joint, the labrum, a fibrous ring of cartilage which extends from the glenoid fossa, providing a deeper receptacle for the humeral head. The capsule tissue that surrounds the joint also helps maintain stability, while the rotator cuff muscles that move the shoulder also provide a significant amount of protection for the shoulder joint.
When the head of the humerus is dislocated from its socket dislocations of the shoulder occur. Dislocations in younger people tend to arise from trauma and are often associated with sports or falls, while older patients are prone to dislocations because of gradually weakening of the ligaments and cartilage that supports the shoulder.
When the shoulder is in a vulnerable position anterior dislocations often occur. A common example is when the arm is held over the head with the elbow bent, and a force is applied that pushes the elbow backward and levers the humeral head out of the glenoid fossa. This scenario can occur with throwing a ball or hitting a volleyball. Anterior dislocations also occur during falls on an outstretched hand. An anterior dislocation involves external rotation of the shoulder; that is, the shoulder rotates away from the body.
Posterior Shoulder Dislocation
Posterior dislocations are uncommon. They are often associated with specific injuries like lightning strikes, electrical injuries, and seizures. On occasion, this type of dislocation can occur with minimal injury in the elderly, and often the diagnosis is missed in this case.
Dislocated Shoulder Treatment
Putting a dislocated shoulder back in place can be difficult and painful. Painkillers or anesthetic may be required. Specific exercises for dislocated shoulder and general shoulder strengthening may be recommended by your doctor or physical therapist.