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The shoulder is the most commonly dislocated joint in the human body. The incidence of shoulder dislocation is increasing.1 Recurrence is common and occurs in as many as 67% of cases.2 Patients often mention a painful, weak arm and a shoulder that readily dislocates with trivial movements. These disabling symptoms can lead to multiple hospital admissions, decreased ability to participate in high level activities, fewer employment opportunities, and a reduction in overall health.3 The “unstable shoulder” has therefore become a relatively common problem seen in primary healthcare, with a reported incidence rate of 2.8%.4
The aim of this review is to provide a simple framework for the clinical assessment, investigation, and treatment of the unstable shoulder for non-specialists and to highlight key patient groups that benefit from early specialist input.
How does a shoulder become unstable?
When a shoulder joint is dislocated by external force (a traumatic dislocation), the structures that normally provide stability stretch, tear, or detach from the glenoid or the humeral head, or both (box 1). These structures either heal in a non-anatomical position or fail to heal. This increases the risk of future episodes and further damage to these structures.5
Dislocation—complete loss of contact between joint surfaces that requires a reduction manoeuvre to restore normal anatomy. This may be acute (first time), recurrent (any subsequent event), or persistent (locked)
Subluxation—partial loss of contact between joint surfaces
Shoulder instability—abnormal movement of the humeral head resulting in subluxation or dislocation from the glenoid cavity. This may be associated with varying degrees of pain
Shoulder joint laxity—asymptomatic movement of the humeral head on the glenoid cavity at the upper end of the normal physiological range
Several classification systems have been developed for shoulder instability, but a lack of supporting evidence has prevented any one of them …
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