Multi-Directional Instability of the Shoulder

Unstable shoulders that slip in their sockets

The shoulder joint is a complex joint that is structured to allow more motion than any other joint in the body. This joint mobility is generally well-controlled and stable, but it can be too mobile in some people, which may predispose to shoulder dislocation. People whose shoulder does not sit as tightly as it should within the joint are said to have shoulder instability.

Shoulder instability is a condition where the ball of the ball-and-socket shoulder joint can come out of the socket. Sometimes the ball comes partially out of the socket—a condition described as a shoulder subluxation. And if the ball comes completely out of the socket, this is a shoulder dislocation.

There are two general types of shoulder instability:

  • Traumatic Instability: Traumatic shoulder instability occurs due to an acute injury to the shoulder, such as a fall or sports injury. The shoulder is forcefully pulled out of its socket, and often must be placed back into position with special maneuvers, sometimes requiring anesthesia. A traumatic dislocation can damage the ligaments that hold the ball in the socket, making the shoulder prone to dislocating again in the future.
  • Multi-Directional Instability: Multi-directional instability (MDI) occurs when the shoulder joint is loose within the socket. There is not necessarily a traumatic event that causes the instability, but rather the shoulder has a tendency to shift excessively, causing pain and limited function in the joint. Often, people who have symptoms of multi-directional instability complain of clunking or shifting of the shoulder with overhead movements.
Chiropractor treating patient’s shoulder
ADAM GAULT / SPL / Getty Images

Three Factors of Shoulder Stability That Contribute to MDI

There are three factors that contribute to the stability of any joint in the body. These include:

  • Bone anatomy: The bones of the shoulder contribute very little to the stability of this joint. The shoulder socket is very shallow, and without other structures to hold it in place, the ball would not stay in position. Compare this to the hip joint, which has a very deep socket, a shape that contributes to the stability of the ball in the socket.
  • Static stabilizers: The static stabilizers are the ligaments that surround the joint. Ligaments connect two bones together. Ligaments are flexible (they can bend), but not elastic (they do not stretch). Shoulder instability is associated with torn ligaments of the shoulder joint. Multi-directional instability is often caused by loose ligaments. In fact, there are genetic conditions that can affect the ligaments and cause severe multi-directional instability.
  • Dynamic stabilizers: The dynamic stabilizers are the muscles and tendons around the shoulder. These muscles include the rotator cuff, a group of muscles that surrounds the ball of the shoulder. Dynamic stabilizers are flexible, and they are also elastic. Many people with multi-directional instability can strengthen the dynamic stabilizers to compensate for loose ligaments.

Symptoms of multi-directional shoulder instability include pain and instability with overhead activities. Most people who have symptoms related to multi-directional instability participate in athletics that involve overhead movements, including swimming, gymnastics, and softball. Young women are most commonly affected by multi-directional instability.

Treatment

The treatment of MDI is different from treatment for traumatic instability of the shoulder. Most often, people can recover from multi-directional instability with non-surgical treatments; this includes high-level, competitive athletes.

Treatment should be focused on strengthening the dynamic stabilizers of the shoulder joint. In addition, multi-directional instability is associated with inadequate shoulder mechanics—specifically, the scapular (shoulder blade) movements are not well-coordinated with the shoulder movements. Shoulder joint function can often improve by restoring normal scapular motion and strengthening the dynamic stabilizers, including the rotator cuff.

Numerous studies have shown that, with effort, the vast majority of patients can recover from multi-directional instability with a focused shoulder rehabilitation program. About 85% of patients who undergo such a program will report good results. However, some people don't improve, and may ultimately decide to have shoulder surgery.

Surgery

Surgical procedures for MDI are considered for patients who have persistent symptoms of shoulder instability despite non-surgical treatments. Most often, the surgery involves tightening the ligaments that surround the shoulder. This can be done with a minimally invasive arthroscopic surgery or with standard surgical incisions.

The best surgery for multi-directional instability is a capsular shift or capsular plication, which are procedures that tighten the shoulder capsule. And a rotator interval closure is a procedure that closes the gap between two of the rotator cuff muscles.

Thermal shrinkage, using heat probes to cauterize soft-tissue in the shoulder to tighten the joint capsule, is a procedure that is no longer used but was popular not long ago. Thermal shrinkage procedures had very poor results and often required further surgical treatment. If you have had thermal shrinkage treatment, you might need surgery if your symptoms recur.

Rehab following surgery for multi-directional instability usually lasts for several months. Initially, after surgery, the shoulder is immobilized to allow the tightened tissues to heal. Then motion is started to regain mobility, followed by strengthening exercises. Most athletes are allowed to resume full activity within 6 months.

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