The glenohumeral joint of the shoulder is the most commonly dislocated joint in the human body.
Over 95% of glenohumeral dislocations are anterior. Violent external rotation in abduction levers the head of the humerus out of the glenoid socket, avulsing anterior bony and soft tissue structures in the process (the Bankart lesion). As the final, posterior part of the humeral head exits the joint, it often collides with the anterior rim of the glenoid, creating a bony indentation at the back of the humeral head (the Hill Sachs lesion).
In a large series of patients under the age of 40 years, Hovelius et al. reported that 54% of anterior dislocations were associated with a Hill Sachs lesion. The presence of a Hill Sachs lesion increases the risk of recurrent dislocation.
The presence of an associated greater tuberosity fracture is more common in the older patient. Sparks et al.4 have also reported a strong correlation between vascular injury in shoulder dislocation and a fracture of the greater tuberosity with only 1% of arterial injuries being associated with dislocation without fracture.
Peripheral nerve injuries following anterior dislocation are common with about 10% patients suffering injury to the axillary nerve.
Between 14–65% of anterior dislocations are also associated with rotator cuff tears with the incidence of this complication again increasing in older patients. Many authors recommend ultrasound screening of patients with first-time dislocations over the age of 40 years.
Hovelius et al. found that the risk of re-dislocation varied inversely with the age at the time of primary dislocation with over a third of patients under the age of 20 years requiring eventual surgery.
Simonet et al.,27 in 1984, described a similar recurrence rate. Both age and athletic activity were shown to be important to the risk of recurrence.
|Age at dislocation (years)||Risk of recurrence|
|<20||Up to 95%|
Patients who do not experience repeat dislocation may well suffer from recurrent subluxation of the joint that limits their overall activity levels.
In those patients who suffer recurrent dislocation, arthroscopic visualisation of the shoulder joint would now be regarded as the gold standard diagnostic technique. MRI scanning is an alternative non-invasive investigation for shoulder injury.
In 1996, Hovelius et al.1 reported moderate or severe osteoarthritis in 8.7% of shoulders in patients who had sustained their first dislocation under the age of 40 years. These authors found that moderate-to-severe osteoarthritis occurred regardless of how the patient had been treated or whether recurrence had occurred.
In 2006, Ogawa et al. reported a high incidence of osteoarthritis in patients with traumatic anterior instability for whom surgery was planned. Plain X-ray in this series revealed osteoarthritis in 11% of cases whereas CT scan revealed osteoarthritis in 31% of cases. The ability of CT to detect osteoarthritic changes missed on plain X-ray suggests that some earlier studies may have underestimated the rate of post dislocation osteoarthritis.