• The shoulder is one of the most mobile joints in the body
• Instability of the shoulder can occur for a variety of reasons
• Depending on the instability pattern treatment may require surgery, physiotherapy or both

What is shoulder instability?

The shoulder performs a vital role in allowing us to position our hands in the space around us, in order to perform the variety of tasks that we perform during our daily lives. As the ball and socket joint of the shoulder (known as the glenohumeral joint) is so mobile, this makes it one least stable joints in the body.

Why does it happen?

The ball and socket joint of the shoulder (known as the glenohumeral joint) can be come unstable after high energy trauma, such as during a fall or a tackle, where the structures that normally control its stability are torn. In individuals with a high degree of flexibility (sometimes known as generalized hypermobility) the shoulder may be inherently lax or become more troublesome after minor or more repetitive injury.

X-ray of an acute anterior shoulder dislocation

What structures are damaged in shoulder instability?

To provide stability, the shoulder relies on the labrum (the lip liner that deepens the socket); joint capsule and ligaments, as well as the co-ordinated action of the muscles around the shoulder. In a traumatic shoulder dislocation, the humeral head (ball) is usually dislocated anteriorly (to the front) out of the glenoid (joint socket). This commonly results in tearing of the labrum and damage to the ligaments.

Labrum and glenohumeral ligaments

In certain arm positions, this may result in these structures becoming unable to help contain the head in the glenoid. In some cases, the anterior rim of the glenoid can become fractured and this can make the symptoms of instability worse.

What treatments are available for shoulder instability?

The appropriate treatment for shoulder instability is dependant on a number of factors including the type of instability; the pattern of structures injured, and the anticipated types and levels of activity that the individual wishes to undertake. In a traumatic instability, it may be necessary to repair the damaged structures, with either an arthroscopic stabilisation (keyhole surgery), or open procedure. Physiotherapy is also necessary following surgery to rehabilitate the shoulder.

If the dislocation has occurred without trauma, or with only minor trauma, or if the age and activity levels of the individual make further dislocation unlikely, it may be that the instability can be treated successfully with physiotherapy.