Anterior shoulder instability is an injury to the shoulder joint so that the upper arm (humerus) is displaced from its normal position in the center of the socket (glenoid) and the joint surfaces no longer touch each other. The most common dislocation (>90percent) is anterior, where the humerus is in front and below the glenoid. Because the shoulder has more motion than any other large joint in the body, it is the most commonly dislocated large joint.

The shoulder is like a golf ball on a golf tee. A few of the many structures that provide shoulder stability include the cartilage rim (labrum), which helps provide depth to the socket; the capsule, with thickenings that are the ligaments of the shoulder; and the muscles of the rotator cuff, which surround the shoulder.

Shoulder dislocation

To dislocate the shoulder, the rotator cuff muscles need to be stretched or torn, the capsule and ligaments need to be stretched, and often the labrum is pulled off the glenoid. Subluxation of this joint is also common in sports; this is when the ball of the humerus does not stay centered in the socket with shoulder motion and feels like it will to slip out of place.

Subluxation of the shoulder causes overuse of the rotator cuff muscles trying to keep the shoulder in the center of the socket, resulting in rotator cuff symptoms. Further, fatigue of the rotator cuff muscles as the deltoid muscle contracts may push the humeral head up to the roof of the shoulder, pinching the subacromial bursa and supraspinatus tendon (part of the rotator cuff).

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How does anterior shoulder instability occur?

• Direct blow to the shoulder or backward force on an extended arm or elbow
• Repetitive throwing motion or swimming
• End result of a severe shoulder sprain
• Congenital abnormality (you are born with it), such as a shallow or malformed joint surface
• Powerful muscle twisting or violent muscle contraction

Some people can willfully produce a recurrent dislocation.

What increases the risk?

• Contact sports (football, wrestling or basketball)
• Sports that involve repetitive overhead activity, such as baseball, volleyball or swimming
• Sports that require forceful lifting, hitting or twisting
• Previous shoulder dislocations or sprains
• Shoulder fracture
• Repeated shoulder injury of any kind
• Poor physical conditioning (strength and flexibility)

What are the symptoms of anterior shoulder instability?

• Severe pain in the shoulder at the time of injury
• Loss of shoulder function and severe pain when attempting to move the shoulder
• Feeling like the shoulder will to slip out of place
• Tenderness, deformity (fullness in the armpit and prominent roof of the shoulder) and swelling
• Pain upon moving the shoulder, especially when reaching overhead; pain with heavy lifting; pain that awakens at night
• Loss of strength
• Numbness or paralysis in the upper arm and deltoid muscle from pinching, stretching or pressure on the blood vessels or nerves
• Crepitation (“crackling”) feeling and sound when the injured area is touched or with shoulder motion
• Decreased or absent pulse at the wrist because of blood vessel damage (rare)

How is anterior shoulder stability treated?

Non-operative treatment: After reduction (repositioning of the bones of the joint) by trained medical personnel, treatment consists of ice and medications to relieve pain. Immobilization by sling or immobilizer for 3 to 8 weeks is usually recommended to protect the joint while the ligaments heal. After immobilization, stretching and strengthening of the stiff, injured and weakened joint and surrounding muscles (due to the injury and the immobilization) are necessary. These may be done with or without the assistance of a physical therapist or athletic trainer.

Operative treatment: Reduction usually can be performed without surgery; surgery may be needed to restore the joint to its normal position, while also repairing ligaments.

Surgery for shoulder instability is reserved for people who have recurrent shoulder dislocations or subluxations that affect activities of daily living or sports activities; these patients have usually tried an appropriate rehabilitation program for at least three to six months with symptomatic recurrent shoulder dislocation or subluxation. Surgery is occasionally recommended for some individuals after the first dislocation. Traumatic anterior dislocations have up to an 80 percent likelihood of recurrent dislocations, particularly in young patients. The likelihood of success of a rehabilitation program is only 20 percent in this group, whereas older patients or patients with an anterior dislocation that is not associated with trauma may have up to 80 percent success with rehabilitation. Surgery may also be performed in a patient who has had a prior operation for shoulder instability.

The goal of surgery is to stabilize the shoulder to prevent further subluxations or dislocations. One of the reasons the shoulder is the most commonly dislocated major joint is that it has more motion than any other major joint. Tightening the shoulder joint may reduce some shoulder motion. Stabilizing the shoulder is done by reattaching the labrum to the glenoid (socket) and tightening the capsule and ligaments. Less often, other structures may be moved or used to replace or give additional support to the ligaments of the shoulder. Recurrent dislocations or subluxations without fracture are rarely associated with arthritis. Thus, the timing of surgery in relation to the injury is not critical.

Different techniques are in use at this time. There are arthroscopic techniques and open-incision techniques. The overall goal is to reattach the labrum to the glenoid (when it is detached) and tighten the capsule and ligaments. One of the most popular open techniques involves going between the deltoid and pectoralis muscles to get to the subscapularis muscle, which covers and is partially attached to the capsule of the shoulder. The subscapularis muscle-tendon is split either in line with its fibers or all or part of it is removed from the arm bone. The capsule is separated from the subscapularis muscle and tendon. The capsule is then cut and the labrum repaired to the glenoid (when necessary) with sutures (threads), with or without surgical anchors, which are inserted into the glenoid rim. If the capsule and ligament are stretched, the shoulder is tightened by folding the excess capsule underneath itself and stitching it together.

Arthroscopic techniques involve using small incisions (arthroscopy portals) to repair the labrum to the glenoid (when necessary) with sutures (threads), with or without surgical anchors, which are inserted into the glenoid rim. If the capsule and ligaments are stretched, the shoulder is tightened either by folding the excess capsule underneath itself and sewing it together or by using heat to shrink it.

Other techniques do not try to replicate the normal anatomy of the shoulder capsule and ligaments. These include moving muscle to reduce shoulder motion or moving bone from another area and using the bone to prevent shoulder dislocations.

What are the complications of treatment?

Possible complications of operative treatment include:

• Surgical complications not specifically associated with this injury, such as pain, bleeding (uncommon), infection (<1percent), nerve injury (uncommon), stiffness, problems with anesthesia, and inability to return to previous level of pre-injury activity.

When can you return to your sport/activity?

With appropriate reduction (repositioning of the joint) and immobilization for three to six weeks, healing of ligaments can be expected in six weeks. The potential for repeated shoulder dislocations depends on the amount of trauma necessary to cause the first dislocation, age at the time of injury (younger age at the time of first dislocation leads to a higher risk of recurrent dislocations; if you are under 18 years old at first dislocation, there is a more than 90 percent risk of another dislocation of the same shoulder), and associated shoulder injury.

If customary treatment does not prevent a recurrence, athletic activities should be modified until surgery can be performed to fix the problem. Return to sports depends on the type of sport and the position played, as well as the quality of the ligaments and capsule at the time of repair. A minimum of three months is necessary after surgery before return to sports. Full shoulder motion and strength are necessary before returning to sports.

How can anterior shoulder instability be prevented?

• Appropriately warm up and stretch before practice or competition
• Maintain appropriate conditioning:
  • Cardiovascular fitness
  • Shoulder strength
  • Flexibility and endurance
• For participation in contact sports, wear protective shoulder pads