There are broadly two reasons why we suffer from shoulder instability. In the first, there are structural causes, either because the capsulolabral mechanisms have been damaged by a major injury, or because the capsulolabral structures are already deficient, predisposing the shoulder to develop instability as a result of minor injury or repetitive micro-trauma or as a result of some action such as throwing a ball. The second cause is that of the development of unbalanced muscle recruitment around the shoulder – as opposed to muscle weakness – which result in the h
umeral head being displaced upon the glenoid.
Shoulder instability is when the ball and socket joint is not controlled well. When the ball is sliding around its socket too much it can cause pain and in some cases come out of the socket and dislocate. Sometime the ball does not completely dislocate and is only partially out and can feel locked. With a wiggle it often returns to is normal position. This is called a subluxation.
There are 3 types of shoulder instability.
The most common form of instability is caused by trauma, such as a fall. The large force causes structural damage to the ligaments and socket rim (labrum). This can lead to repetitive dislocations in some people. Shoulder rehabilitation may reduce the chances of this by training the rotator cuff to fully recover and compensate. In the younger population (below 28 years old) the chances of re-dislocation are much higher and they may require surgery.
The second type of instability is caused by excessive laxity of the shoulder ligaments and poor muscle control. This is not only of the rotator cuff, but also the muscles that control the scapula on the rib cage and to the rest of the body. It is difficult to keep the ball in a socket that is not controlled. This instability is known as atraumatic instability. It requires very specialist rehabilitation to achieve the complex muscle control. In some rare cases surgery can aid the muscle retraining process by tightening up the capsule and ligaments.
The third type is very rare and called “abnormal muscle patterning.” This is when the big powerful muscles that attach around the shoulder, activate inappropriately and out of sequence. This causes vary large forces that the rotator cuff simply cannot compete with. This type of instability requires very specialist physiotherapy. We aim to reteach these muscles to activate in a normal way and rewriting their programming. Occasionally, the first 2 types of shoulder instability may develop these characteristics and it is important that this is identified early and addressed.
Due to the complex nature and wide spectrum of symptoms of shoulder instability shoulder surgeons and shoulder physiotherapists work very closely together to manage this condition. Communication is key.