Shoulder dislocation and AC joint injury

The shoulder is one of the most mobile joints in the body, allowing a wide range of movement for daily activities and sports. However, this flexibility also makes it vulnerable to dislocation and injury, particularly in the shoulder joint and the acromioclavicular (AC) joint, where the collarbone meets the top of the shoulder. Distinguished orthopaedic surgeon Professor Duncan Tennent, who practises at at Cleveland Clinic London Hospital, provides an expert look at understanding the differences between these injuries, how they're treated and details when to seek medical advice.

What is a shoulder dislocation?

A shoulder dislocation occurs when the ball of the upper arm bone (the humeral head) comes out of its socket in the shoulder blade. This can happen due to a fall, sports injury or sudden impact. Because the shoulder joint is shallow, it can dislocate forwards, backwards or downwards, though most dislocations occur at the front of the joint.

Symptoms include:

Severe pain immediately after injury;
Loss of shoulder movement;
A visible deformity or bulge at the front of the shoulder;
Swelling or bruising;
Numbness or tingling down the arm.

A full dislocation means the joint has completely come out of place, while a partial dislocation (subluxation) means it has slipped partway out of the socket.

What is an AC joint injury?

The acromioclavicular (AC) joint is the junction between the collarbone (clavicle) and the top of the shoulder blade (acromion). It can be injured through direct impact, such as a fall onto the shoulder or during contact sports. AC joint injuries are often described as “shoulder separations” rather than dislocations because the damage involves tearing of the ligaments that hold the joint in place, rather than the bone moving out of its socket.

Symptoms can include:

Localised pain at the top of the shoulder;
Swelling or bruising;
A bump or visible separation where the collarbone sits higher than normal;
Pain when lifting the arm or lying on the affected side.

How are these injuries diagnosed?

A physical examination and medical history help to identify the type of injury. Imaging tests, such as X-rays or MRI scans, confirm the diagnosis, and show the extent of damage to bones, ligaments and surrounding tissues.

What treatments are available?

Treatment depends on the severity of the injury and whether it is a shoulder or AC joint problem.

For shoulder dislocations:

The joint is gently repositioned, a process called reduction.
Immobilisation with a sling allows tissues to heal.
Physiotherapy strengthens the muscles around the shoulder to prevent recurrence.
In some cases, particularly with repeated dislocations, surgery may be required to stabilise the joint.

For AC joint injuries:

Mild separations can often be treated with rest, ice and physiotherapy.
More severe separations involving complete ligament rupture may require surgery or reconstruction.

Recovery and long-term care

Rehabilitation plays a key role in both shoulder and AC joint recovery. Physiotherapy focuses on regaining movement, rebuilding muscle strength and improving stability. Most people recover well with proper treatment, although those with recurrent dislocations may benefit from surgical stabilisation to reduce the risk of further injury.

When to see a specialist

If shoulder pain follows a fall, collision or sudden movement, or if there’s visible deformity or weakness, it’s important to seek medical attention as soon as possible. Early assessment by an orthopaedic or sports medicine specialist ensures accurate diagnosis, appropriate treatment and the best chance of a full recovery.

If you're looking for gold-standard surgical treatment for shoulder injuries, make an appointment with Professor Tennent at Cleveland Clinic London Hospital via his Top Doctors profile.