What is acromioclavicular joint separation?
Acromioclavicular (AC) joint separation (or dislocation) is an injury where the ligaments that stabilise the connection between the collarbone (clavicle) and the highest point of the shoulder blade (acromion) are stretched or torn, leading to partial or complete displacement of the joint. When the ligaments are damaged, the clavicle may shift upward while the shoulder blade drops slightly, creating a visible bump on the top of the shoulder in more severe cases. This injury can cause pain, swelling, and reduced shoulder function, particularly with lifting or cross-body movements.
Causes
Acromioclavicular (AC) joint separation is most commonly caused by a direct impact or force applied to the top of the shoulder. This often occurs when an individual falls directly onto the shoulder, such as during cycling accidents, contact sports like rugby or football, or slips onto a hard surface. The force drives the shoulder blade downward while the collarbone remains relatively fixed, placing stress on and potentially tearing the ligaments that stabilise the AC joint. Less commonly, the injury can result from a fall onto an outstretched arm or repetitive stress in overhead or heavy lifting activities, which may weaken the surrounding structures over time and make the joint more vulnerable to injury.
Symptoms
Shoulder pain (top of shoulder): Sharp or aching pain located directly over the AC joint, often worsening with movement or pressure
Visible bump or deformity: In moderate to severe cases, the collarbone may appear raised, creating a noticeable “step” or bump on the shoulder
Swelling and bruising: Inflammation and bleeding around the injured ligaments can cause swelling and discolouration around the top of the shoulder
Tenderness to touch: The area over the AC joint is often very sensitive, and even light pressure can be painful
Reduced shoulder movement: Pain and instability can limit the ability to lift the arm or move it across the body
Weakness in the arm: Shoulder instability and pain may reduce strength, making it difficult to lift or carry objects
Pain with cross-body movement: Bringing the arm across the chest often increases pain due to compression of the injured joint
Diagnosis
Your surgeon will taking a detailed history of how the injury occurred, often focusing on a direct blow to the top of the shoulder and the onset of pain, swelling, or visible deformity.
This is followed by a physical examination, where the surgeon assesses tenderness over the AC joint, checks for a visible bump or step, and evaluates shoulder movement and strength, particularly with cross-body adduction which often reproduces pain.
Imaging
To confirm the diagnosis and determine the severity of the injury, imaging is used. X-rays are the primary investigation and may show displacement of the clavicle relative to the acromion, while comparison views of both shoulders can help highlight subtle differences. In more complex cases, CT or MRI scans may be used to assess associated soft tissue damage and guide treatment planning.
Treatment
Conservative (non-operative)
The decision between conservative and operative management of acromioclavicular (AC) joint separation depends on the severity of the injury, the patient’s functional demands, and the presence of associated damage. Lower-grade injuries (Types I and II), where the ligaments are stretched or partially torn but the joint remains largely aligned, are typically managed conservatively with rest, sling immobilisation, pain control, and gradual physiotherapy. Many Type III injuries may also be treated non-operatively, especially in individuals with lower physical demands, as good functional outcomes are often achieved without surgery.
Conservative management of acromioclavicular (AC) joint separation focuses on pain relief, protection of the joint, and gradual restoration of shoulder function. Initially, the arm is usually supported in a sling to reduce movement and allow the injured ligaments to begin healing, along with the use of ice and analgesics to control pain and swelling. As symptoms improve, physiotherapy is introduced to restore range of motion through gentle exercises, followed by progressive strengthening of the rotator cuff and scapular stabilising muscles to improve shoulder control and stability. Activity modification is important during recovery, avoiding heavy lifting, overhead movements, or contact sports until adequate strength and comfort return. Most patients with low- to moderate-grade injuries recover well with this approach and regain good shoulder function without the need for surgery.
Surgical treatment
Surgical management is more commonly considered in higher-grade injuries (Types IV–VI), where there is significant displacement of the clavicle, complete ligament disruption, or instability. Surgery may also be recommended for younger, active individuals, overhead athletes, or manual workers who require optimal shoulder strength and stability, particularly if persistent pain, weakness, or functional limitation remains despite rehabilitation.
The goal of surgery is to realign and stabilise the clavicle in relation to the acromion and reconstruct the damaged ligaments that support the joint. This can be achieved using techniques such as ligament reconstruction with grafts, fixation devices, or suture-based systems that hold the joint in its correct position while healing occurs. In some cases, minimally invasive arthroscopic methods are used, while others may require open surgery depending on the severity of the injury. After the procedure, the arm is usually immobilised in a sling for a period of time, followed by a structured rehabilitation program to restore range of motion, strength, and full shoulder function.
Recovery
When can I return to daily activities?
This depends on the activity, the exact nature of your surgery and your progress with your rehabilitation.
Most people can:
- Return to office or light duties (no use of the arm at chest height or above, no repetitive duties, no heavy lifting) at 10-14 days. Sling should be worn when using a computer / doing admin work
- Walking for exercise from 3 weeks
- Driving – approximately 3-6 weeks, 15-30 minutes as you feel safe and confident. When you are no longer using the sling and have full control of the vehicle. No truck driving until 4 months
When can I participate in leisure activities?
Your ability to start these will be dependent on the range of movement and strength that you have in your shoulder following the operation. Please discuss activities in which you may be interested with your physiotherapist or surgeon. Start with short sessions, involving little effort and gradually increase.
General examples are:
- Cycling – 4 to 6 weeks
- Jogging – 12 weeks
- Swimming – gentle breast-stroke 12 weeks, freestyle variable
- Light sports/racquet sports using non-operated arm – 10 weeks
- Racquet sports / golf using operated arm – 16 weeks
- Contact or collision sports which includes horse riding, soccer, martial arts, football and rock climbing – 6 to 9 months