Shoulder instability is a term which describes a pathological increase in transalatory movement of the humeral head (ball in the socket) which interferes with function of the shoulder joint. True shoulder instability generally occurs because of structural damage to, or congenital abnormality of the shoulder joint. This is quite different to hypermobility or poor rotator cuff control, although these issues may further compound the symptoms experienced.
Instability is traditionally though of in terms of damage to the ligaments of the shoulder complex, which physically limit the movement of the humeral head. Indeed, damage may occur to the ligaments of the shoulder however it often also involves damage to a combination of; capsule, labrum, cuff tendons and bony elements.
Shoulder instability is really a spectrum of disorders. At one end is recurrent micro instability as a result of loss of humeral head control, in the middle recurrent subluxation of the shoulder, where it starts to dislocate but ‘pops’ back in and at the other end is recurrent frank dislocation of the shoulder joint. Instability tends to be further classified into either unidirectional or multidirectional instability.
Unidirectional instability is the most common form of shoulder instability. It refers to conditions where the shoulder is lax or unstable in one direction only. Commonly this is associated with trauma to the shoulder such as a fall, where the humeral head has been forced in a particular direction and has stretched or damaged the passive constraints of the shoulder designed to limit movement in this direction. Typically, in these conditions pain and dysfunction of the shoulder is associated with quite specific movements and positions.
Conservative management of these conditions is very often successful and should always be the first port of call. In more severe cases and particularly in the case of recurrent dislocation of the shoulder, surgical repair of the damaged structures to stabilise the shoulder may be considered to restore function.
Multidirectional instability of the shoulder is a much less common but more complex condition. In these cases, the shoulder is unstable in multiple directions and is commonly associated with generalised laxity of the shoulder. While onset may be associated with significant trauma, often a minor trauma or period of increased training is enough to lead to a painful and dysfunctional shoulder.
Clinically patients tend to present with pain and dysfunction in a much wider range of movements and positions than those with unidirectional instability. The instability events are usually subluxations rather than dislocations of the shoulder and can generally be reduced by the patient. These events may or may not be painful and often happen several times a day.
Due to the complex combination of directions in which the shoulder can be unstable, these conditions often do poorly with surgery. The mainstay of treatment tends to be quite a structured and gradual rehab program, aimed at maximising strength and control of the stabilising muscles of the shoulder in gradually more provocative positions. Due to the more complex nature of the dysfunction, guidance by an experienced physio is often pivotal to successful outcomes.
Article by Jim Burke
