AC Joint Injuries


by Dr Marcus Chia - Shoulder and Elbow Surgeon
The AC (acromioclavicular) joint is formed between the end of the collarbone (clavicle) and a specific part (acromion) of the shoulder blade (scapula). Most people can identify their AC joint by feeling the bony lump on top of their shoulder that is typically covered by the bra strap in women. Stability of the joint depends upon multiple ligaments and muscles.

AC joint injuries represent nearly half of all sporting shoulder injuries. They usually occur as a result of a fall on the tip of the shoulder. Injury may damage the ligaments, muscles and cartilage within the joint. The collarbone or acromion can also be fractured. Also, growth plate injuries can occur in children and young adults.

The degree of injury is dependent on the amount of energy transferred to the joint. This results in a spectrum of injuries from mild shoulder sprains to complete joint dislocation. The most common classification system has 6 types:

Type 1: swelling and tenderness but no visible deformity, normal xrays

Type 2: slight widening of joint on xrays

Type 3: complete dislocation of joint but with muscles still intact

Type 4: collarbone (clavicle) dislocated backwards (posteriorly)

Type 5: muscles detached from end of collarbone (clavicle), the collarbone (clavicle) can be felt just under the skin (subcutaneous)

Type 6:
rare, collarbone (clavicle) dislocated downwards (inferiorly)

Symptoms of AC joint injury vary according to the severity of injury. This includes pain, swelling and deformity (lump on top of the shoulder). The skin may be tented. Commonly bruising and skin abrasions are seen. Shoulder movements are painful, particularly lifting the arm or bringing it across the body.

Physical examination helps to assess the severity of the injury and to rule out other concomitant injuries. Xrays are essential to diagnose and classify AC joint injuries. In some cases a CT or MRI scan may be needed.

Initial treatment consists of controlling the pain and swelling with ice and simple analgesics. The shoulder should be rested in a simple sling. Most AC joint injuries can be treated without surgery. An early and graduated rehabilitation program is instituted once the shoulder pain has subsided. This is followed by strengthening and endurance. Contact sports and heavy lifting should be avoided for 2 to 3 months to allow for ligament healing.

Surgery is reserved for more severe injuries and for those that fail non-surgical treatment. The goal of surgery is to reduce the joint dislocation and stabilise the joint. Multiple techniques have been developed to achieve these goals. Dr Chia utilises a key-hole (arthroscopic) technique, where possible, in order to avoid the large incisions necessary for open reconstructions and achieve a faster recovery.

Post-operatively the shoulder will be placed in a sling for comfort. Ice is encouraged to control pain and swelling. Active and passive range of motion exercises (below shoulder level) are commenced under the supervision of a physiotherapist. Lifting anything more than 2 kg should be avoided. Strengthening can be initiated at 3 months. Once full range of motion and strength are obtained, return to sports and manual labour is permitted.
Any surgical or invasive procedure carries risks. The information provided here is for general educational purposes only. For more information on AC joint injuries, or to learn more about arthroscopic AC joint repair, please contact the office of Dr Marcus Chia, Sydney, Australia, Orthopaedic Shoulder and Elbow Surgeon.

(02) 8014 4252

Clinic Locations


Dee Why
Peninsula Orthopaedics
Level 1
812 Pittwater Road
Dee Why NSW 2099

Mona Vale
Mona Vale Rooms
Suite 502, 20 Bungan Street
Mona Vale NSW 2103

Wahroonga
Northside Orthopaedics
San Clinic
Level 4, Suite 403
185 Fox Valley Road
Wahroonga NSW 2076

Bella Vista
HSS Orthopaedics
Hospital for Specialist Surgery
Level 1, Suite 1
17-19 Solent Circuit
Norwest Business Park
Bella Vista NSW 2153