→ a shoulder that is weakened by full or partial dislocation.
The shoulder joint is made up of a ‘ball’ and a ‘socket’ (the glenohumeral joint). It’s surrounded by a rim of tissue (the labrum) that deepens the socket and keeps it stable. Sometimes, however, the ball pops out of the socket, potentially damaging the surrounding tissue (damage to the labrum is known as a Bankart Tear) or even nearby bone (a Bony Bankart lesion) as it does so. If it pops out completely, we call this dislocation. If partially, we call it subluxation.
There are three principle causes. The most common is a traumatic dislocation, where the joint is pulled out of place during an impact, such as a rugby tackle, or after a fall onto an outstretched hand. Epileptic fits and even electric shocks can sometimes also cause traumatic dislocations. Instability can also be caused by long-term, repeated movements. Over time, these movements may stretch and weaken the shoulder muscles, causing the joint to become ‘looser’ and more vulnerable to dislocation or subluxation. A third cause is ‘positional non-traumatic instability’, where an abnormal or lax muscle structure causes the joints to be more easily displaced.
Traumatic dislocations are most common in younger men, particularly sportsmen, and when a shoulder has been dislocated once, weakening of the muscles in the area makes it more vulnerable to being dislocated again in the future. This is known as chronic shoulder instability. Dislocation caused by repeated movements is most common in people whose jobs involve overhead work, or athletes whose sports involve swimming or throwing.
A shoulder dislocation is usually obvious – it will be very painful, and the arm is likely to look and feel physically out of place. Subluxations can be more subtle and gradual; you may feel a sense of looseness in the shoulder, as if something is slipping inside the joint. The pain may be particularly noticeable at night, when lying on the affected shoulder. Shoulder instability can also lead to swelling or redness, or pins and needles in the arm (because the nerves have been stretched).
Shoulder instability can usually be diagnosed after discussion of your history and a physical examination. The doctor will feel for looseness in the shoulder, and look for signs of pain when the arm is gently moved towards its dislocation point. X-rays may be needed to identify damage to bone. MRI scans can help to diagnose soft tissue tears.
Treatment for shoulder instability varies depending on the kind of damage sustained. With a first-time dislocation, the arm will be put back into position (this is known as reduction), then placed in a sling to heal, followed by physiotherapy to strengthen the muscles that keep the shoulder in its joint. Non-traumatic instability may also be treated with physiotherapy and an exercise or ‘muscle re-training’ programme. Maintaining the programme, potentially for several months, is key to a successful recovery. Chronic instability and tissue tears may require surgery. Surgical procedures range from tightening the shoulder capsule to reduce looseness in the arm (although this is rare), to a Bankart Repair to repair labrum damage and restabilise the joint.