Shoulder Instability / Shoulder Dislocation

Shoulder instability refers to the condition where the glenohumeral shoulder joint is too loose; allowing the humeral head to move or slide around too much within the socket. This can result in frequent dislocations or subluxations, where the shoulder partially slips out of place.

A shoulder dislocation occurs when the humeral head comes out of the shoulder socket (glenoid). A shoulder dislocation typically happens when there is a significant force that forces the ball of the humerus out of the socket. When the shoulder dislocates, it can damage both the glenoid and the humeral head, causing small fractures or dents in the bone or injuries to the surrounding soft tissue. Most commonly, dislocations result in damage to the labrum. In addition, dislocations can stretch out and damage the joint capsule, making it more likely that the shoulder will dislocate again.

There are three types of shoulder dislocations:

Anterior Shoulder Dislocation:

This is the most common type of shoulder dislocation. It occurs when the humerus is forced forward out of the shoulder socket. Anterior dislocations often result from trauma such as a fall on an outstretched arm or a direct blow to the shoulder.

Posterior Shoulder Dislocation:

Less common than anterior dislocations. In posterior dislocations, the humerus is forced backward out of the shoulder socket. This type of dislocation can occur due to specific trauma or as a result of muscle imbalances, particularly weakness in the muscles at the front of the shoulder.

Inferior Dislocation (Luxatio Erecta):

This is a rare type of dislocation where the humerus dislocates downward, below the shoulder joint. It is often caused by a significant force applied to the arm when it is in an abducted position (arm raised sideways). Inferior dislocations are less common than anterior and posterior dislocations but can result in severe nerve and vascular complications.

Shoulder instability can be caused by traumatic injuries, repetitive overuse of the shoulder, or a genetic predisposition. Instability may arise from ligament or labral tears, weakening of the shoulder muscles, or anatomical factors, such as a history of Ehlers Danlos, contributing to an inherently unstable joint. Athletes competing in sports with high shoulder demands, such as baseball pitchers, tennis players, or swimmers are at a higher risk of shoulder instability due to the repetitive shoulder motion required for the respective sport.

Common symptoms of shoulder dislocation include:

• Significant shoulder pain
• Weakness
• Swelling
• Loss of range of motion.
• Popping sensation with arm movement.
• Inability or difficulty moving the arm.
• Potential numbness of the arm.
• Apprehension with extreme shoulder positions.

If you experience a shoulder dislocation or instability, you should seek medical attention right away, regardless of if the shoulder remains dislocated or not. Even if the shoulder goes back into place by itself, there may be damage to the surrounding structures that need treatment.

The combination of a detailed history, comprehensive physical examination, x-rays, an MRI, and sometimes a CT scan is the key to a successful diagnosis of a shoulder dislocation and shoulder instability.

Dr. Chahla and his team will ask you several questions to gather a history of your shoulder symptoms, including how you injured the shoulder, how many dislocations you have had in the past, activities that make your symptoms worse, and what activities you would like to be able to do in the future.

Dr. Chahla and his team will next perform a physical exam of the shoulder that will include an evaluation of strength, range of motion, and a thorough assessment to make sure there are no injuries to the nerves or blood vessels in your arm. In addition, there are several specific tests that Dr. Chahla can perform to determine if there is any increased motion or laxity (load and shift test, sulcus sign), or sensations of instability (apprehension and relocation tests).

An MRI is an important diagnostic imaging test to evaluate the full extent of the injury, including damage to the labrum and cartilage of the shoulder. The MRI also allows Dr. Chahla to fully assess surrounding shoulder structures, including the biceps tendon and rotator cuff.

A CT scan of the shoulder may be ordered to better assess for any potential injury to the bone of the glenoid that may have occurred as the humeral head dislocated and relocated into the shoulder socket.

These bone injuries include:

Hill-Sachs Lesion:

This is a depression or divot in the head of the humerus that can occur when the humeral head impacts against the glenoid during a dislocation. It is more common in anterior dislocations. Hill-Sachs lesions can contribute to instability and may be a factor in recurrent dislocations.

Glenoid Fracture:

The force of a shoulder dislocation can sometimes cause a fracture in the glenoid, which is the socket of the shoulder joint. Glenoid fractures are more likely to occur in high-energy traumas and may require surgical intervention for stabilization.

Greater Tuberosity Fracture:

The greater tuberosity is a bony prominence on the humerus where the rotator cuff muscles attach. A shoulder dislocation can result in a fracture of the greater tuberosity, especially in cases of significant trauma.

Lesser Tuberosity Fracture:

This type of fracture involves the smaller bony prominence on the anterior aspect of the humerus where the subscapularis muscle attaches. Lesser tuberosity fractures are not as common but can occur in association with shoulder dislocations.