The shoulder is known as a “ball and socket” joint, with a large ball and shallow socket to allow for extensive range of movement. It can be likened to a golf ball sitting on a golf tee. A number of factors help the shoulder to remain stable during normal movement. These include the muscles acting around the shoulder which help centre the head on the socket, the joint capsule and the labrum. The labrum is a cartilage ring that surrounds the glenoid socket, providing the “lip” to the golf tee.
A shoulder can dislocate out the front (most common), back or bottom and usually will require a visit to the emergency department for it to be relocated.
What are the causes?
The majority of first time dislocations occur due to a significant injury, such as falling on an outstretched hand. Many sporting activities and particularly contact sports put the shoulder at risk of dislocating. If the shoulder has dislocated once it has a higher chance of coming out again, particularly if you are young (less than 25 years of age). This type of dislocation will normally damage the labrum and joint capsule.
Some people can dislocate their shoulder with minimal or no trauma. This is more common in adolescent girls and usually relates to a problem in how the muscles are working around the shoulder. It is very unlikely any damage to the joint would have occurred with this type of dislocation.
What are the symptoms?
It is usually very obvious when a shoulder dislocates following trauma. It is very painful and should be treated by the emergency department to ensure that your shoulder is safely put back into joint. You will be treated in a sling following the dislocation but you can get rid of this after one week. Many patients will be able to move their shoulder comfortably within a few weeks following a dislocation. However, it can cause continued pain or continued symptoms of instability.
How is it diagnosed?
X-rays demonstrate a dislocated shoulder well. An MR Arthrogram (where dye is injected into the shoulder and an MRI is performed) is used to look at the internal structures of the shoulder to assess for damage. This does not always have to be done but is useful if surgery is considered. An ultrasound can also be performed to look for muscle damage, particularly in patients over the age of 40.
How is it treated?
Recurrent shoulder dislocations due to trauma are best treated with surgical stabilisation. This is performed through keyhole surgery and is called an arthroscopic shoulder stabilisation. If the dislocations have caused bone loss around the shoulder then a Latarjet procedure can be performed. Shoulder dislocations in patients over 40 years old can cause rotator cuff tears, which may need to be treated in the form of a rotator cuff repair.
Dislocations without a history of trauma are best treated with physiotherapy.