Shoulder joint instability can manifest as a feeling that the joint will dislocate or can manifest in actual repeated dislocations of the shoulder. Often there is a particular position or movement which individuals suffering with shoulder instability are aware of which causes these problems.
Commonly, shoulder instability is caused by a significant trauma to the stabilising structures of the joint. However, shoulder instability can develop without trauma. This is known as atraumatic shoulder instability.
Several causes of atraumatic shoulder instability are seen in clinical practice and it is often a mixed presentation with more than one potential underlying cause:
Flexibility of soft tissue structures across the body is on a wide spectrum. Some individuals are inherently very stiff with their joint and muscle flexibility and others are very flexible. Hypermobility describes a syndrome where an individual can develop various secondary musculoskeletal and sometimes medical problems due to their inherent genetics producing soft tissue which is at the upper end of flexibility. Under normal circumstances, the shoulder joint is held stable by soft tissue capsule, ligaments and tendons. Thus, the shoulder is particularly vulnerable to developing instability secondary to hypermobility of these structures.
Bony abnormalities to the shoulder socket (dysplasia)
During development, all of our joints grow in size and develop a particular shape and contour to their bony structure. Under normal circumstances, the shoulder socket (glenoid) is small and flat to allow a greater degree of movement at the shoulder. In some circumstances, this socket may develop a shape with even less surface area to hold the upper arm bone in the socket rendering the joint susceptible to instability.
Acquired shoulder instability (through repeated sporting activities)
Rather than a congruent bony structure, the shoulder joint is kept stable by several soft tissue structures. The joint capsule at the front and a fibrous deepening to the shoulder socket known as the glenoid labrum as well as the long head of biceps tendon can all become gradually lax with repeated activity. Normally, the activities involve overhead activity with a degree of rotation of the shoulder. Throwing is the most common example of a sporting activity giving rise to atraumatic instability over time.
Specific treatment strategies for atraumatic shoulder instability are similar for those directed at traumatic shoulder instability. However, due to the insidious nature of onset and no large structural defects being present in the majority of cases, rehabilitation exercises can play a large role in cases of atraumatic instability.
Due to the increased frequency of atraumatic shoulder instability being seen in certain types of athletes. Namely, those involve in throwing activities and certain types of sports involving contact shoulder tackling may be prescribed a program of shoulder stability exercises in prior to complaining of symptoms. These proactive shoulder programs are aimed at maintaining optimal muscle patterning and power to the shoulder blade muscles and rotator cuff to prevent any excess movement of the upper arm bone in the shoulder socket. This ensures no laxity will develop to the joint capsule over time.
Rehabilitation exercises for those individuals with current symptoms will generally involve three components. The first is a program of exercises known as proprioceptive exercises which develop the shoulders ability to recognise its current location and joint angles. This is extremely important as when this is optimised muscle co-ordination and timing improve when the shoulder is placed in positions of vulnerability making it less likely to dislocate.
The second exercise component is to optimise the strength of the muscles which support the shoulder blade. The shoulder socket (glenoid) is part of the bony anatomy of the shoulder blade and if these muscles are able to position and stabilise the position of the shoulder socket optimally then this allows the rotator cuff muscles to work to stabilise the shoulder joint more efficiently.
Finally, rehabilitation of the rotator cuff muscles themselves allows the shoulder joint to be able to control the centring of the upper arm bone in the shoulder socket and also resist any rotational forces in an optimal way to help to prevent dislocation.
Depending on patient choice, age (the younger the patient the more likely the need for surgery to adequately stabilise the shoulder) and activity level, If there are continues symptoms following a period of rehabilitation, surgery to correct the any structural fault may be considered.
Many variations of surgery are available and if necessary, a shoulder surgeon will provide more information on any particular options to be considered. In the vast majority of cases the surgery will be completed using a keyhole technique (arthroscopy).
Depending on the structural problems present surgery will repairing the glenoid labrum and then tightening the shoulder joint capsule across the region of instability, securing it to keep it tight. If required various forms of bony block grafts may be used to rebuild a more secure shape to the glenoid.
Shoulder braces may be used as part of a post-surgical strategy to ensure no laxity develops when getting the shoulder moving initially and on initially returning to sports specific activities.