What is it?
Shoulder instability occurs when the structures surrounding the joint are compromised, and the ball is not secure within the socket. The joint feels loose and becomes unreliable, which can lead to partial dislocation (subluxation), or total dislocation. The shoulder joint is susceptible to instability due to its large range of movement.
Why does it occur?
There are a number of reasons why should joints can become unstable, the most common being as result of the shoulder being forced out of its joint during some kind of trauma. The force of such an injury can result in damage to the soft tissues around the joint, such as the ligaments and labrum (known as a Bankart tear), or the bony head of the shoulder (Hill-Sachs). Any of these types of damage leave the shoulder vulnerable to dislocation in the future.
Some people, however, may suffer what is known as atraumatic dislocation. This is instability within the shoulder when only a small force is applied, and occurs when the surrounding structures are lax because of overuse or due to a congenital condition, such as being double-joined. In these cases, the joint will often relocate without assistance.
There is additionally a further group of patients who suffer with inappropriate muscle recruitment; the stability of the shoulder joint comes in part from precise synchronised muscle contractions and relaxations during movement. Each of the 30 muscles moving and stabilising the shoulder need to be activated at specific times. When there is imbalance in this function, what is known as instability muscle patterning can occur.
What are the symptoms?
You may feel pain within the joint, long after an initial injury, or that your shoulder gives way easily. You can also experience numbness around the top of the arm.
How is it diagnosed?
A detailed history and examination is essential to determine the mechanism of injury and therefore appropriate treatment modality. X-rays and magnetic resonance imaging can then be used to confirm the suspected diagnosis.
How is it treated?
Lifestyle changes and modifying the activities that provokes symptoms are key. Medications that reduce inflammation, such as non-steroidal anti-inflammatories like Aspirin and Ibuprofen, can be beneficial. Most importantly, physiotherapy exercises that aim to improve strength in the muscles supporting the shoulder, can improve shoulder stability. With non-surgical treatment, it can take a few months before you feel any benefit.
This is most commonly performed using arthroscopy; a type of surgery in which, using a special instrument, a very small hole or holes are made in order to look at a joint, and sometimes to repair the joint at the same time.
The One Orthopaedics team specialists
Consultant Orthopaedic Specialist FRCS (Tr & Orth)