Shoulder dislocations and instability
What is instability?
The shoulder joint is a ball and socket joint. Under normal circumstances the ball is sat centrally on the socket, a bit like a golf ball sitting on a golf tee. When the shoulder joint becomes unstable the ball has a tendency to slide off the socket, either to the front, the back, or downwards. The shoulder is the most flexible joint in the human body. This flexibility comes at the expense of stability and, as a result, the shoulder joint is the most commonly dislocated joint in the body.
What causes shoulder instability?
The stability of the shoulder is dependent upon the shape of the ball and socket joint, ligaments connecting the ball to the socket, and muscles surrounding the joint. Damage to, or abnormalities of, one or more of these structures may compromise the stability of the
Current thinking describes shoulder instability of three varieties:
1. Shoulder dislocations most commonly occur as a result of a traumatic event. A great deal of force is required to dislocate the shoulder, and often the shoulder has to be put back into joint (reduced) in hospital under sedation. As a result of the dislocation there may be tearing of the ligaments or tendons of the shoulder and/or fractures of the bones.
2. Some individuals are inherently more flexible than others, sometimes referred to as being "double jointed". These people can develop instability of the shoulder without precipitating trauma.
3. A third type of instability, termed "muscle patterning" exists. In these cases instability of the shoulder joint is caused by a lack of muscle coordination as the shoulder joint moves. Certain muscles may be working too hard, or muscles may be activated in the wrong
An individual may have more than one type of instability contributing to their shoulder problem to varying degrees. This makes the assessment and treatment of shoulder instability very complex. It is vital that treatment is tailored to the individual patient. Treating a patient who has a predominantly muscle patterning problem as if they had a traumatic shoulder dislocation is unlikely to be successful.
What problems does shoulder instability cause?
Some people may sustain a traumatic dislocation to their shoulder and, after it has been reduced, the shoulder joint goes on to function normally and does not give rise to further episodes of instability. Certain groups of patients, however, are at an increased risk of further dislocations or symptomatic instability after a first traumatic dislocation. It is well established that male gender, age less than 25, participation in contact sports such as rugby and bone damage all increase the risk of recurrent instability and dislocations.
Symptomatic instability without dislocation
Even if a shoulder does not come fully "out of joint", it may be unstable to the extent that certain movements of the shoulder are difficult due to a sensation of impending dislocation (apprehension). This often accompanied by pain and a feeling of weakness.
Wear and tear (arthritis)
It is likely that patients who have had shoulder dislocations have an increased risk of developing shoulder arthritis later in life. It is logical that the greater the number and frequency of dislocations, the greater the damage is done to the joint surface and the greater the risk of arthritis. Similarly, if a shoulder can be prevented from having ongoing episodes of instability, it seems logical that the damage will be less. Having said this, no scientific study has demonstrated that treatment of instability reduces the incidence of arthritis.
What can be done to treat shoulder instability?
As mentioned above, shoulder instability is very complex and can be due to more than one cause, or a combination of causes. There is no treatment for shoulder instability that is 100% effective in every case. Your surgeon will help you decide which treatment is likely to be most effective.
Treatments can be divided into those involving surgery and those not involving surgery:
Irrespective of the cause of shoulder instability, physiotherapy is a vital component of treatment. In cases of atraumatic and muscle patterning instability, physiotherapy is effective in strengthening and coordinating groups of muscles to work effectively and thus reducing episodes of instability. Many cases of traumatic instability are also effectively treated with physiotherapy.
In cases of traumatic instability where there is a high risk of further episodes or when a patient has suffered repeated dislocations surgery may be effective in improving symptoms. Through a series a small keyholes, arthroscopic surgery allows the repair of torn ligaments deep inside the shoulder joint. Small plastic plugs attached to sutures are inserted into the bone. The sutures can be passed through the ligaments to reattach them to the bone. Although relatively rare, sometimes the damage to the bones of the shoulder joint is so severe that keyhole ligament repair is not appropriate. In these instances a piece of bone from the shoulder blade is moved to the front of the shoulder socket, making it wider and
therefore more difficult for the shoulder to dislocate. This is most commonly performed through a more traditional open incision, rather than a keyhole. Patients with atraumatic or muscle patterning instability do not generally respond well to surgery. In rare cases keyhole surgery can be used to tighten the shoulder joint lining. The effects of this are temporary and only when combined with intensive physiotherapy can this procedure durably improve symptoms