Dr. Peter Johnston

Shoulder Instability

What is shoulder instability?

Shoulder instability refers to the inability of the humeral head (ball) to stay centered on the glenoid (the socket) and is the result of damage to the shoulder ligaments that function to keep the ball centered on the socket. 

Normal shoulder stability requires a complex interplay between bony and soft tissue stabilizing structures. The natural shape of the shoulder joint allows for a wide arc of motion, and therefore only provides a limited amount of inherent stability. As a result, the shoulder relies on soft tissue structures, including the capsule, labrum and glenohumeral ligaments, as well as muscles of the rotator cuff, to maintain stability.

What are common ways the shoulder can become unstable?

Shoulder instability can be caused by a single inciting event, like a dislocation or subluxation, that disrupts the stabilizing soft tissue structures in the shoulder or can be from repeated strenuous use. Violent injuries can be from a football tackle or a motor vehicle accident. In a dislocation the ball comes completely out of the socket.  In a subluxation the ball comes partially out of the socket. Swimming or throwing are examples of instances when repeated use causes laxity within the shoulder joint. 

The soft tissue structures within the shoulder joint that are typically injured include the capsule, ligaments and labrum. The labrum is the fibrous cartilage attachment of the capsule that surrounds the socket.  Injury to these structures alters the soft tissue balance of the shoulder and often results in recurrent dislocations or a sense that the shoulder is unstable. Typically, with one dislocation event, the chances of having another are significantly increased.  Patient who are most likely to have recurrent instability are those under the age of 25, males, and athletes who compete in contact sports. Recurrent instability events increase the change of damaging the bone of the glenoid and humeral head, as well as placing the rotator cuff and crossing nerves at risk for injury.  

Patients can also have what is called multi-directional instability, where they feel the shoulder is unstable in many different directions.  These patients will often have others signs of hyperlaxity, or too much motion of the shoulder and other joints (fingers, wrist, and elbows).  Typically, these patients have been told they are “double-Jointed.” 

Symptoms associated with shoulder instability 

Shoulder instability is a common cause of shoulder pain.  Patient will also complain of weakness in the affect arm. During a dislocation event you may need someone to reduce the joint back in place, such as an emergency room physician. With recurrent instability, the shoulder may intermittently come partially or completely out of sockets. Patients will often become very cautious of using the unstable arm in fear of causing another instability event. 

Diagnosis

Diagnosis is based on physical exam, x-rays, and an MRI. A set of x-rays is usually ordered to make sure there are no fractures (broken bone) in the shoulder. Commonly, a small fracture in the area of the dislocation can occur on the humeral head, called a Hill-Sachs lesion.  A MRI can sometimes be helpful to confirm the tear of the ligament off of the bone (Bankart lesion), and evaluate for other shoulder problems. Usually, the MRI is performed with dye (gadolinium) to help see the ligaments.

Treatment

The treatment primarily depends on the patient’s age, activity level, and number of dislocations of the shoulder. When a patient dislocates their shoulder for the first time, they can commonly be treated in a sling with early rehabilitation. However, for patients with repeat episodes of instability, the usual treatment is surgery to fix the ligaments.

Shoulder instability is usually repaired with arthroscopic techniques. In shoulder instability surgery, the damaged labrum and ligaments are identified and then repaired back to the socket. This is usually performed by using suture anchors (a screw with sutures attached) to sew the ligaments back in place.

Occasionally, if the damage is severe or longstanding or associated with a bony fracture, the surgery needs to be performed with an open incision. This procedure is called a “Latatjet procedure,” and uses the coracoid bone of the scapula as a bone graft to fix the bony fracture on the socket.