Understanding Shoulder Dislocations and Rotator Cuff Injuries

Shoulder dislocations account for almost 50% of all joint disorders in Singapore. Most commonly, these dislocations are anterior and occur because of trauma.

A shoulder dislocation is a painful and disabling injury joint. Most fractures are anterior (forward), but the shoulder can dislocate posteriorly. Doctors usually identify the type of dislocation based on the position of the humeral head to the glenoid (shoulder socket) at the time of the diagnosis.

Anatomy of the Shoulder

The shoulder has unique anatomy that allows a wide range of movements needed for stretching, reaching lifting, throwing, and other motions. It comprises of the humerus found on the upper arm bone, the scapula on the shoulder blade, and the clavicle (the collarbone). The roof of the shoulder is formed by acromion, a part of the scapula.

Four joints make up the shoulder. The primary shoulder joint, called the glenohumeral joint, is formed where the ball of the humerus fits into a shallow socket on the scapula.

The acromioclavicular (AC) joint is where the clavicle meets the acromion. The sternoclavicular (SC) joint supports the connection of the arms and shoulders to the main skeleton on the front of the chest. The scapulothoracic joint is formed where the shoulder blade glides against the thorax (the rib cage). This joint is important because it requires that the muscles surrounding the shoulder blade work together to keep the socket lined up during shoulder movements.

There are several important ligaments in the shoulder. Ligaments are soft tissue structures that connect bones to bones. A joint capsule is a watertight sac that surrounds a joint. A group of ligaments that connect the humerus to the glenoid forms the joint capsule. These ligaments are the primary source of stability for the shoulder. They hold the joint in place and keep it from dislocating.

The labrum is a cartilaginous structure inside the shoulder that is attached almost entirely around the edge of the glenoid. The labrum creates a deeper cup for the ball of the humerus to fit into and helps prevent dislocation.

The Rotator Cuff

Four rotator cuff tendons connect the deepest layer of muscles to the humerus. This group of muscles lies just outside. The rotator cuff muscles and tendons also help keep the shoulder joint stable by holding the humeral head in the glenoid socket.

Another crucial muscle is the deltoid muscle that is found on the outer layer of the shoulder muscle. The deltoid is the largest, strongest muscle of the shoulder. The deltoid muscle takes over lifting the arm once the arm is away from the side.

Being a very mobile joint, the shoulder is more vulnerable to dislocation than other joints. Forceful motions that cause soft tissue structures to tear or rupture lead to dislocation. Once the shoulder has been dislocated the first time, there is a high probability of a second shoulder dislocation. It’s essential for the patient to get rotator cuff treatment immediately and after that do exercises to strengthen the injured shoulder and prevent another occurrence of damaging the joint. 

Vanessa Shelton is a 21-year-old local activist who enjoys bridge, listening to music and cycling. He is intelligent and caring, but can also be very lazy and a bit untidy.

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