Shoulder instability means that the structures in and around the shoulder are unable to fix the head of the upper arm bone (humerus) in the socket in the correct manner. Particularly in the case of fully extended movements, the ball threatens to dislocate from the socket, which is accompanied by significant symptoms.
People with hypermobility and athletes involved in overhand sports are at increased risk of developing instability symptoms of the shoulder.
Description of the condition
The shoulder is a very mobile joint. The head of the humerus is very big compared to the small socket in which it rests. As a result, it is very important that the surrounding tissues fix the ball in the socket correctly. If this does not happen, we are at risk of shoulder dislocation.
The upper arm is attached to the socket of the shoulder blade by capsules and ligaments. Together, they provide passive stability. The labrum also contributes to this. This is the boney ring of cartilage located around the edge of the socket.
The rotator cuff muscles play an important role in the active stability of the shoulder. They provide good fixation of the head of the humerus in the shoulder socket. Poorly functioning rotator cuff muscles allow for too much movement in the joint, allowing for easier dislocation of the joint.
The result of poorly functioning rotator cuff muscles is that the joint capsule, the ligaments and the labrum have to absorb the forces of the fully extended movements. If these movements are too forceful or occur too often, these tissues can become damaged.
Cause and origin
Shoulder instability can develop gradually or in one go as a result of an accident or injury.
If the symptoms develop gradually, the cause is often a sport or activity involving a lot of overhand (explosive) movements. The frequent fully extended movements of overhand throwing, tennis, volleyball and swimming can damage the capsules and ligaments of the shoulder.
A traumatic cause of the symptoms results in (sub)luxation of the shoulder following an accident or fall. The shoulder dislocates partially or completely. This is referred to as acute shoulder luxation. Luxation can damage the capsules, ligaments and the labrum.
Signs & symptoms
Instability of the shoulder is characterised by pain with elevation or outward rotation of the upper arm. The patient experiences a feeling of instability in the shoulder joint, particularly with fully extended movements.
Training of the rotator cuff muscles usually has a favourable effect on the stability of the shoulder joint.
Nugteren, K. van & Winkel, D. (2007). Onderzoek en behandeling van de schouder. Houten: Bohn Stafleu van Loghum.