Shoulder dislocation is where the ball of the shoulder (head of the humerus) comes entirely out of the socket (glenoid cavity of the scapula).
Subluxation refers to a partial dislocation of the shoulder. The ball does not come fully out of the socket and naturally pops back into place shortly afterwards.
More than 90% of shoulder dislocations are anterior dislocations. This is where the head of the humerus moves anteriorly (forward) in relation to the glenoid cavity. This can occur when the arm is forced backwards (posteriorly) whilst abducted and extended at the shoulder. Picture someone reaching up and out to try and catch a heavy rock travelling towards them.
Posterior dislocations are associated with electric shocks and seizures.
TOM TIP: Exam questions might challenge you to distinguish between anterior and posterior dislocations. The answer is almost certainly an anterior dislocation unless the patient has had a seizure or an electric shock.
Associated Damage
The glenoid labrum surrounds the glenoid cavity. The labrum is a rim of cartilage that creates a deeper socket for the head of the humerus to fit into. When the shoulder dislocates, the labrum can tear along one edge.
Bankart lesions are tears to the anterior portion of the labrum. These occur with repeated anterior subluxations or dislocations of the shoulder.
Hill-Sachs lesions are compression fractures of the posterolateral part of the head of the humerus. As the shoulder dislocates anteriorly, the posterolateral part of the humeral head impacts with the anterior rim of the glenoid cavity. Part of the humeral head is damaged, making the shoulder less stable and at risk of further dislocations.
Axillary nerve damage is a key complication. The axillary nerve comes from the C5 and C6 nerve roots. Damage causes a loss of sensation in the “regimental badge” area over the lateral deltoid. It also leads to motor weakness in the deltoid and teres minor muscles.
Fractures can occur alongside shoulder dislocations, affecting the:
- Humeral head
- Greater tuberosity of the humerus
- Acromion of the scapula
- Clavicle
Rotator cuff tears may occur with shoulder dislocations, particularly in older patients.
TOM TIP: Axillary nerve damage is a common association with anterior dislocations to remember for your exams. This knowledge may be tested in MCQs, where you are asked to identify the nerve, location of sensory loss or muscle affected by weakness.
Presentation
Patients with a shoulder dislocation usually present after the acute injury. They will almost certainly be aware that the shoulder is dislocated. Shortly after the shoulder is dislocated, the muscles will go into spasm and tighten around the joint.
They will hold their arm against the side of their body. The deltoid will appear flattened, and the head of the humerus will cause a bulge and be palpable at the front of the shoulder.
It is important to assess patients with a shoulder dislocation for:
- Fractures
- Vascular damage (e.g., absent pulses, prolonged capillary refill time and pallor)
- Nerve damage (e.g., loss of sensation in the “regimental patch” area)
Apprehension Test
The apprehension test is a special test to assess for shoulder instability, specifically in the anterior direction. It is likely to be positive after previous anterior dislocation or subluxation of the shoulder. This may be performed after recovery from any acute injuries.
The patient lies supine. The shoulder is abducted to 90 degrees, and the elbow is flexed to 90 degrees. The shoulder is then slowly externally rotated in this position while watching the patient. As the arm approaches 90 degrees of external rotation, patients with shoulder instability will become anxious and apprehensive, worried that the shoulder will dislocate. There is no pain associated with the movement, only apprehension.
Investigations
X-rays may be used in an acute presentation to confirm a dislocation and exclude fractures. They are not always required before reduction, depending on the clinical findings and risk of a fracture (see local policies and ask seniors). X-rays are performed after reduction to confirm the shoulder is reduced and assess for fractures.
Magnetic resonance arthrography is an MRI scan of the shoulder with a contrast injected into the shoulder joint. This can be used to assess the shoulder for damage (e.g., Bankart and Hill-Sachs lesions) and planning for surgery.
Arthroscopy involves inserting a camera into the shoulder joint to visualise the structures.
Acute Management
Ideally, the shoulder should be relocated as soon as safely possible. Muscle spasm occurs over time, making it harder to relocate the shoulder and increasing the risk of neurovascular injury during relocation.
Acute management of a shoulder dislocation involves:
- Analgesia, muscle relaxants and sedation as appropriate
- Gas and air (e.g., Entonox) may be used, which contains a mixture of 50% nitrous oxide and 50% oxygen
- A broad arm sling can be applied to support the arm
- Closed reduction of the shoulder (after excluding fractures)
- Dislocations associated with a fracture may require surgery
- Post-reduction x-rays
- Immobilisation for a period after relocation of the shoulder
There are various options for closed reduction of shoulder dislocations. See local guidelines and get experienced senior input when managing shoulder dislocations and for guidance on relocation techniques.
Ongoing Management
There is a high risk of recurrent dislocations, particularly in younger patients.
Physiotherapy is recommended to improve the function of the shoulder and reduce the risk of further dislocations.
Shoulder stabilisation surgery may be required to improve stability and prevent further dislocations. This may be an arthroscopic or an open procedure. Underlying structural problems are corrected, such as:
- Repairing Bankart lesions
- Tightening the shoulder capsule
- Bone graft using bone from the coracoid process to correct a bony injury to the glenoid rim (Latarjet procedure)
- Correcting Hill-Sachs lesions (Remplissage procedure)
There is a prolonged period of recovery and rehabilitation after shoulder stabilisation surgery (3 months or more).
Recurrent instability and dislocations can occur in up to 20% of patients after surgery.
Last updated August 2021