Shoulder Instability

Shoulder instability develops when the stabilizing structures that hold the shoulder joint in place, the ligaments, labrum, and surrounding muscles, become stretched, torn, or weakened. The rotator cuff muscles and tendons also play a key role in maintaining joint alignment during movement.

When these stabilizing structures are compromised, the ball of the humerus can slip out of position, either partially or fully. Some patients experience this due to an acute injury, such as a fall or sports accident, while others develop instability gradually from repetitive overhead activities or naturally loose ligaments. Shoulder instability can affect people of all ages, but it is especially common in athletes who participate in contact or overhead sports, such as football, baseball, volleyball, swimming, or tennis.

Patients with shoulder instability often describe a feeling that the shoulder is “loose,” “slipping,” or “about to pop out.” The symptoms can vary in severity depending on whether the instability is acute or chronic. Common symptoms include:

• Shoulder pain, especially during movement or activity
• A sensation of the shoulder shifting or moving out of place
• Weakness in the shoulder or arm
• Limited range of motion or difficulty lifting the arm overhead
• Recurrent dislocations or subluxations
• Swelling or bruising after an episode of instability
• A feeling of apprehension when moving the arm in certain positions, particularly overhead or behind the back

Some patients also report numbness, tingling, or temporary weakness in the arm after a dislocation. Repeated episodes can cause ongoing discomfort even at rest and may lead to more significant shoulder damage over time.

Shoulder instability can be caused by trauma, repetitive motion, or inherent looseness of the joint. The causes typically fall into three main categories:

1. Traumatic injury – A sudden force, such as a fall onto an outstretched arm, collision, or direct blow to the shoulder, can cause the ball of the humerus to dislocate. This often results in tearing of the labrum or ligaments, weakening the shoulder’s ability to stay stable in the future.
2. Repetitive stress – Athletes and individuals who perform repeated overhead motions may gradually stretch or wear down the ligaments and joint capsule that stabilize the joint. Over time, this can cause microtears and lead to chronic instability even without a single major injury.
3. Multidirectional or congenital laxity – Some people naturally have looser ligaments or more flexible joints, a condition called hyperlaxity. This can make their shoulders more prone to slipping out of place, especially with repetitive use or minor trauma.

A dislocation can damage several structures, including the labrum (a tear known as a Bankart lesion), rotator cuff tendons, and bone surfaces. Each recurrence increases the risk of further injury and arthritis in the joint.

If shoulder instability is left untreated, it can lead to chronic pain, repeated dislocations, and long-term complications, including damage to the labrum or cartilage wear that can results in degenerative changes in the shoulder and post-traumatic arthritis. The shoulder may become progressively weaker and more difficult to control, affecting daily activities and athletic performance.

Athletes may find that their ability to throw, lift, or perform overhead movements declines. In severe cases, the shoulder may become unstable even during routine daily activities such as reaching or dressing.

Diagnosis of shoulder instability begins with a thorough review of medical history including inquiry about the number and frequency of dislocations and subluxation, and the level of pain and weakness. and a comprehensive physical examination. Dr. Kevin Collon, an orthopedic specialist at Keck Medicine of USC, will perform a comprehensive physical examination carefully evaluating shoulder function and the degree of instability. specific maneuvers are performed to assess joint laxity and safely reproduce symptoms. Diagnostic imaging—such as X-rays, MRI, or CT scans—may also be ordered to identify labral tears, bone loss, or other structural damage contributing to the instability.

Patients should seek professional evaluation if they experience repeated shoulder dislocations, persistent pain, or the feeling that the shoulder could “give out” during activity. Early assessment can help prevent further damage and improve long-term outcomes.