Shoulder Instability

What Is Shoulder Instability?

Shoulder instability happens when the ball of the shoulder isn't restrained properly by ligaments or cartilage and slides out of the shoulder socket, either partially or fully.

Types of Shoulder Instability

An unstable shoulder can happen for various reasons. These are the most common types of instability in the shoulder:

• Dislocation or subluxation: When the ball of the shoulder, known as the humeral head, moves out of place, it can be a full dislocation or a partial, known as a subluxation and humerus subluxation. This is most likely to occur during an acute injury.
• Labrum tear: If the labrum, cartilage that helps keep the shoulder head in place, tears or loosens it can lead to a shoulder dislocation. A labrum can tear during an acute injury or impact or because of repetitive overuse.
• Genetic condition: Shoulder instability can happen due to a genetic condition that creates loose ligaments, increasing the chances of a weaker or unstable shoulder.

Shoulder Subluxation vs Dislocation

Subluxation of the shoulder is a partial dislocation of the shoulder. A humeral head subluxation occurs when the ball of the shoulder doesn't fully dislocate from the glenoid fossa but has shifted out of its normal position. In a full dislocation, the humeral head of the shoulder fully detaches from the glenoid fossa or shoulder socket. A dislocation is most common with a sudden impact injury, while a subluxation often happens with repetitive motions that weaken the muscles, ligaments and cartilage.

What Causes Shoulder Instability?

The shoulder joint is a ball and socket joint that connects the bone of the upper arm (humerus) with a shallow socket (glenoid cavity) of the shoulder blade (scapula).

Dislocations or subluxations can occur due to a variety of motions or injuries, such as:

• A fall that puts force on an outstretched arm, pushing the humeral head out of the shoulder socket
• Repetitive overhead motion, such as throwing a baseball, that causes the arm to go too far behind the body

Any event that pulls the humeral head away from the glenoid cavity can stretch or tear the cartilage (labrum), ligaments and muscles designed to keep the humerus from dislocating. When the capsule tears from the glenoid rim, the shoulder can become unstable and dislocate or subluxate repeatedly. Shoulder instability is when your shoulder is especially prone to recurrent dislocation or subluxation.

Chronic Shoulder Instability

Chronic shoulder instability can start to happen at any point. Even people who have no history of shoulder problems can suffer from chronic shoulder instability after an injury. Some people recover fully. Patients whose injuries do not heal properly can end up with chronic shoulder instability due to torn or stretched ligaments, cartilage and muscle.

The causes of chronic shoulder instability include:

• A sudden trauma, whether a hard hit or fall, that forces the shoulder out of its socket and tears or stretches the ligaments. Once loose, the shoulder is more prone to movement and can lead to a chronic state of instability.
• Repetitive motions, such as an overhead throw, loosen the shoulder capsule, resulting in chronic shoulder instability.
• A genetic condition of loose ligaments, known as hyperlaxity, that leads to chronic shoulder instability without an injury.

Shoulder Instability Symptoms

People with shoulder instability can have a variety of symptoms and sensations.

• Looseness. Often described by patients as their shoulder giving out, slight shoulder subluxations can cause the patient to feel a loss of ability to use the joint, even momentarily
• Pain with activity. Shoulder instability can cause pain during certain motions or shoulder positions
• Weakness. An unstable shoulder may feel weaker than before, especially during activity
• Bruising and swelling. At times the shoulder instability can worsen and cause bruising and swelling
• Decreased range of motion. An unstable shoulder may not have the same range of motion as a healthy shoulder

Shoulder Instability Diagnosis

Diagnosing shoulder instability often starts with a physical exam by a doctor. A doctor will check for weakness, range of motion and looseness. They will also ask you about injuries and shoulder instability history.

For a more detailed look at the shoulder, a doctor may use further testing:

• Magnetic resonance imaging (MRI) or computed tomography scan (CT scan)
• MRI or CT scan can be performed after dye is injected into the shoulder joint (arthro-MRI or arthro-CT)
• Examination under anesthesia followed by arthroscopy

Shoulder Instability Treatments

Some patients who dislocate their shoulder fully recover after the injury and do not have recurrent instability, particularly if older and not active in sports. Young people, especially athletes, are prone to have recurrent dislocations and subluxations and often need surgery to correct the shoulder problem. Learn more about how Mass General Brigham specializes in the care of shoulder injuries, including shoulder instability.

Nonsurgical treatments

Before surgery, a doctor may advise exploring one or more nonsurgical shoulder instability treatments:

• Physical therapy and shoulder instability exercises designed to strengthen muscles over the course of multiple weeks
• Activity modification to reduce the stress on the shoulder and avoid symptom-causing motions
• Anti-inflammatory drugs to help with swelling and pain

Shoulder Instability Surgery

An unstable shoulder joint can be repaired by reattaching the torn capsule to the glenoid rim. This is called a Bankart repair. The muscles are separated to expose the shoulder capsule and, if the capsule is found to have torn away from the bone, three holes are made in the glenoid rim. Stitches are passed through each hole and through the capsule and tied, securing the capsule to the glenoid rim. The capsule heals back to the bony rim and prevents the shoulder from re-dislocating. It takes several months for the capsule to heal back to the bone. During this time, extreme shoulder motion should be avoided so that the stitches are not torn.

The torn capsule can also be repaired with the aid of an arthroscope without opening the shoulder. If the size of the tear is small and future physical demands placed on the shoulder are low, this may be a good alternative. If the tear is large and the shoulder is highly unstable, open repair is stronger, especially in athletes.

The success rate of the Bankart repair is approximately 97%. If there is a fracture of the glenoid rim (Bankart lesion) and a compression fracture of the humeral head (Hill-Sachs lesion), there is an increased risk of recurrent instability following repair. Two nerves are at risk during surgery since they are near the operative field, but they are rarely injured. As with any surgical procedure, there are potential risks. The incidence of infection is less than 0.5%. The shoulder can lose some motion after surgery, especially if the shoulder needs to be over-tightened because of excess laxity.

FAQs

Related Conditions and Treatments:

• Shoulder tendonitis
• Rotator cuff injuries
• Shoulder injury FAQs
• Shoulder surgery FAQs