Instability is one of the more common causes of shoulder problems. The shoulder is the most mobile joint in the body, and that mobility comes at a cost. The ball at the top of the upper arm bone sits against a relatively shallow socket on the shoulder blade, held in position by the labrum, the joint capsule, the ligaments and the surrounding muscles. When those structures are damaged, or when they are naturally looser than usual, the joint can move further than it should.
Instability covers a wide spectrum. At one end are frank dislocations, where the ball comes completely out of the socket and usually has to be put back into place, or reduced, under anaesthetic in hospital. At the other end are subtle subluxations, where the joint slips only partly out of position and settles again by itself, but still causes pain, a sense that the shoulder is giving way, and loss of confidence in the arm.
There are two major categories of shoulder instability: traumatic instability, which follows an injury, and multidirectional instability, which occurs in people whose soft tissues are naturally very loose. The two patterns behave differently and are managed differently, so working out which one is present is the first step in planning treatment.
Types of shoulder instability
Traumatic anterior dislocation
This is the most common pattern of shoulder instability. It follows an injury in which the shoulder dislocates out the front of the joint. It is seen most often in young men who play high-impact sports, although it can affect anyone who sustains a high-energy injury to the shoulder.
The main difficulty after a traumatic anterior dislocation is the risk of it happening again. Published series report that young patients who return to active sport have a high rate of further dislocations, and that recurrent dislocation becomes the usual pattern rather than the exception. The risk falls as the age at the time of the first dislocation increases. Individual results vary.
Because of that recurrence risk, stabilisation surgery is often recommended in young, active patients after a first dislocation rather than after several. This pattern is covered in more detail on the anterior shoulder instability page.
Multidirectional instability
Multidirectional instability usually affects people who are naturally very flexible. Surgeons describe this as ligamentous laxity, meaning the collagen in the ligaments and capsule is more stretchy than normal. In this group the shoulder may come out the back of the joint as well as the front, and many patients describe the shoulder having been loose from the time of their first episode rather than following a single significant injury.
Symptoms
- A dislocation, where the shoulder comes fully out of joint and will not go back without help, usually under anaesthetic in a hospital emergency department.
- Subluxation, where the shoulder slips partly out of position and relocates itself, often with a sudden sharp pain.
- A feeling that the shoulder is about to give way, particularly with the arm out to the side and rotated backwards.
- Pain and loss of function between episodes.
- Loss of confidence in the arm, so that sport, overhead work and some sleeping positions are avoided.
Causes
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Injury. A high-energy force on the shoulder, such as a fall, a tackle, or a heavy load taken with the arm extended, levers the ball out of the socket and tears the structures that hold it in place, most often the labrum at the front of the joint.
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Ligamentous laxity. Some people are born with more stretchy collagen, so the capsule and ligaments allow more movement than usual. In these patients the shoulder can become unstable without any significant injury.
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Repeated episodes. Each further dislocation or subluxation can stretch the capsule, damage the labrum and, in some cases, wear away bone from the rim of the socket, which tends to make the shoulder progressively less stable.
Diagnosis
Assessment starts with the history, covering how the shoulder first came out, in which direction, how often it has happened since, and which positions provoke it, followed by examination of movement, strength and overall joint laxity. Both shoulders are examined, because generalised looseness in other joints points towards a multidirectional pattern rather than a purely traumatic one.
Imaging is then used to show what has been damaged. Plain X-rays show the position of the joint and any injury to the bone. MRI normally shows which of the soft tissue structures have torn, in particular the labrum and the capsule. A CT scan is sometimes added when there is concern about loss of bone from the rim of the socket, because significant bone loss changes which operation is appropriate.
Treatment
Non-surgical treatment
After a first dislocation the shoulder is usually rested in a sling for the first few days, until the pain settles, and movement is then restored gradually. Physiotherapy aids recovery of movement, strength and control of the shoulder blade. For multidirectional instability a well-directed strengthening programme is the mainstay of treatment, and many people in this group are managed without surgery.
For traumatic anterior dislocation the position is different. Physiotherapy helps recovery, but there is no good evidence that it substantially reduces the chance of the shoulder dislocating again, because the structures torn during the dislocation do not reliably heal back in the right position.
Surgical treatment
Surgery for instability aims to repair the structures that were damaged and to restore the normal restraints to the joint. It is usually performed arthroscopically, through keyhole incisions. The procedure chosen depends on what has been injured and whether bone has been lost from the socket.
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Arthroscopic Bankart repair, which reattaches the torn labrum to the rim of the socket and tightens the capsule. Used where there is a labral tear without significant bone loss.
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Latarjet and labral repair, which transfers a block of bone from the coracoid to the front of the socket, together with repair of the labrum. Used where bone has been lost from the front of the socket.
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Remplissage, which fills a defect in the back of the ball of the shoulder so that it cannot engage on the rim of the socket.
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Stabilisation, for general information about stabilisation surgery and what recovery involves.
Any of these procedures carries risk, including the risks of general anaesthetic, a small risk of infection, a small risk of nerve injury, stiffness, and the possibility that the shoulder becomes unstable again. These risks are discussed in consultation before any decision is made.
What to do next
If your shoulder has dislocated, or if it feels as though it is slipping or giving way, an assessment will establish which pattern of instability is present and what is likely to help. You can read more about the structure of the joint on the shoulder anatomy page, about the most common pattern on the anterior shoulder instability page, and about recovery after stabilisation surgery on the rehabilitation page.
To arrange an assessment, see consultation. The consultation FAQs explain what to bring and what to expect, and the surgery FAQs answer common questions about having an operation. Other shoulder conditions are listed under shoulder injuries and conditions.
This page is general information and is not a diagnosis. Individual circumstances vary, and the right treatment for you can only be determined after assessment. Any procedure carries risk; these are discussed in consultation.
