Shoulder dislocations and instability
The shoulder is one of the most mobile joints in the body and thus it is not surprising that it is prone to dislocations. A number of factors help the shoulder to stay in joint. Very little stability is afforded by the shapes of the involved bones as the shoulder is essentially composed of a ball (the humeral head) perched on a very flat socket (the glenoid). The socket is deepened somewhat by the presence of a lip of soft tissue (cartilage) found around the periphery of the glenoid. This tissue, which is vital to stability, is called the labrum. The labrum is attached to the capsule of the joint which itself has a number of thickenings (ligaments) which are also important for stability. The other important structures assisting stability are the muscles around the joint itself.
Shoulder instability is often sub-classified by specialists into “Traumatic” and “Atraumatic”, dependent on whether or not the instability started with a significant injury to the shoulder.
In this category of instability, the patient will usually give a history of a significant injury as a precipitating event. With this type of injury, there is usually structural damage. If the bones are significantly damaged, the abnormality may be detected on X-ray. However, the vast majority of people with a symptomatic traumatic dislocation will require a special type of MRI to delineate the damage. This is known as an MRI arthrogram (or ‘MRA’). In such an investigation, some dye is placed in the joint prior to the scan. The dye then leaks into any abnormally torn areas or clefts. One of the most import issues that such an MRA will detect is the presence of a tear in the labrum. This is known as a Bankart tear and will be present in the majority of of traumatic dislocations. Bankart lesions are the most common cause of recurrent instability.
Treatment of traumatic instability
This will be dependent on the demands of the patient. For example, an elite rugby player will almost certainly require surgery without delay as they will have at best about a 30% chance of getting through the rest of a playing season without a further dislocation. For other patient groups, particularly those who have a lower risk of re-dislocation, specialist physiotherapy may be recommended, at least as a first line of treatment.
The two main types of operation are an arthroscopic (keyhole) Bankart repair or a Latarjet procedure.
The best type of operation will depend on a number of factors, but some general rules of thumb are:
Arthroscopic repairs are indicated for people with soft tissue damage i.e. a labral (Bankart tear) with either recurrent instability, or often after a single dislocation e.g. in younger people who engage in contact sports.
An arthroscopic Bankart repair involves refixing the torn labrum to the edge of the glenoid using small implants called anchors. The anchors are fixed into the bone of the glenoid and then the attached stitches are passed through the soft tissues. Tensioning the stitches then brings the soft tissues back to their correct attachment on the bone where they then heal.
Click for post-operative rehabilitation protocol
A Latarjet procedure is more often performed for people who have damaged the bone of the socket, particularly if they engage in contact sports. People who have undergone previous stabilisation surgery, but have dislocated again, may also be considered for this option.
Following either type of surgery, the arm will need to be rested in a sling for two to three weeks. Physiotherapy will commence early in this phase and continue until the patient returns to good function. In elite athletes, return to contact sports can be in as little as eight weeks. Average return to contact would be about three months.
With this type of instability (which often affects both shoulders) there is usually no history of a significant injury as a precipitating event.
Causes of this type of instability may include problems with the muscle control around the shoulder (both under activity and over activity of different muscles can contribute); problems with excessive elasticity of the soft tissues can also contribute (eg patients who are “double jointed” or hyper lax).
Other issues with posture, shoulder blade control, and core stability can also be implicated.
Treatment of atraumatic instability
The mainstay of treatment for this type of problem is specialist physiotherapy. It is imperative that the physiotherapist has experience in dealing with these problems. In some cases, usually after a period of appropriate physiotherapy, surgery may be indicated if symptoms persist. This type of surgery is technically demanding to get right and to avoid causing further problems. Skilled post-operative physiotherapy is equally as important.