Updated December 04, 2014.

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Shoulder instability is a condition that can lead to dislocation or subluxation of the shoulder joint, meaning that there is too much mobility of the shoulder joint, and the ball can come out of the socket. In general, there are two categories of shoulder instability:

• Traumatic Shoulder Instability
  Traumatic shoulder instability occurs most often in sports or an injury, such as a fall or car crash. When the shoulder is forcefully dislocated from the joint, the ligaments or tendons can tear; the most common injury pattern after a shoulder dislocation is called a Bankart tear. Traumatic shoulder instability occurs in people who have a normal shoulder joint that's pushed too far, causing damage when the shoulder comes out of joint.

• Multidirectional Instability (MDI)
  Multidirectional instability is different because the should joint is too loose, causing symptoms with even normal activities. The shoulder may dislocate or sublux (come partially out of joint) with even simple movements, not traumatic events. In these situations, the instability is the underlying problem, not a trauma or injury.

Upon diagnosis of multi-directional instability of the shoulder, people typically first try non-surgical treatments. Most often, these treatments will help prevent further episodes of instability by strengthening the muscles surrounding the shoulder to better stabilize the joint. In some individuals, however, even prolonged efforts at therapy may prove unsuccessful. In these patients, shoulder surgery may be recommended.

Shoulder Capsule Surgery

The shoulder capsule is the envelope that surrounds the shoulder joint. It contains several specific thickened parts, or ligaments, that stabilize the shoulder. Typically, patients who have multi-directional instability have laxity of the ligaments, and looseness of the capsule.

The shoulder capsule in these patients is described as having pouches.
Surgery to correct multidirectional instability is aimed at tightening the ligaments and decreasing the overall size of the shoulder capsule. In general, there are two surgical approaches to accomplish this. The traditional surgery happens via an incision over the front of the shoulder, called a capsular shift. A more recent approach is performed arthroscopically, through small incisions with the aid of a camera inserted into the joint.

Open Capsular Shift

An open capsular shift is the more traditional surgery performed to tighten the shoulder joint. In this procedure, an incision is made along the front of the joint, and the muscle in front of the shoulder, called the subscapularis (part of the rotator cuff), is detached to allow your surgeon to see inside the joint. The shoulder capsule is then identified and split; the bottom part of the shoulder capsule is pulled up; and then the top is pulled down to decrease the volume of the shoulder joint.
The advantage of this technique is that it's tried and true. Surgeons have a good ability to visualize the extent to which they tighten the joint, and can significantly reduce the volume of the shoulder capsule. The downside is that recovery is longer, in part because the detachment of part of the rotator cuff.

Capsular Plication

A capsular plication is surgery that is performed arthroscopically. The surgeon inserts a camera into the shoulder joint, and through other small incisions uses sutures to "grab" part of the shoulder capsule and sew it upon itself to tighten the capsular tissue. Some surgeons feel they can see the results of their work better by watching this through the camera, and can more precisely place the sutures that are used to tighten the shoulder.

Best Surgery?

It's not clear if one of these techniques is better than the other; the choice probably depends primarily on your surgeon's preference, since most doctors will feel that they can perform one procedure more reliably. This doesn't mean that his preference is the better one — it just means it's the one your surgeon is most comfortable performing.
We do know that one procedure, called a thermal capsular shrinkage — or thermal capsulorrhaphy — should not be performed. This procedure, popular in the 1990s and even in to the 2000s, uses a heat probe to cauterize and shrink the capsule of the shoulder. A number of bad outcomes resulted from this surgery, so thermal capsular shrinkage is no longer recommended.

<sub>Sources:

Gaskill TR, et al. "Management of Multidirectional Instability of the Shoulder" J Am Acad Orthop Surg December 2011 ; 19:758-767.</sub>