Acromioclavicular (AC) Joint Injury

What is an AC joint injury?

The Acromioclavicular (AC) joint is a common site of injury, particularly for athletes involved in contact and collision sports such as Australian football and rugby (league and union), and throwing sports such as shot put.

Anatomy: The AC joint forms part of the shoulder structure. It is the point at which the lateral end of the clavicle (collarbone) meets with the part of the scapula (shoulder blade) called the acromion process. It can be identified by sight and touch as the pointy protrusion near the top, outer edge of the shoulder.

The joint is surrounded by a joint capsule and receives additional support from the acromioclavicular and coracoclavicular ligaments (the coracoclavicular ligament is made up of the trapezoid and conoid ligaments). These ligaments are commonly damaged in AC joint injuries.

Risk factors

An AC joint injury often results from a direct blow to the tip of the shoulder – such as from an awkward fall or impact with another player – which forces the acromion process downward, beneath the clavicle.

Alternatively, an AC joint injury may result from an upward force transmitted through the long axis of the humerus (upper arm bone), such as a fall that impacts directly on the wrist of a straightened arm. Typically, the shoulder is in an adducted (close to the body) and flexed (bent) position when this occurs.

Signs and symptoms

• Pain at the end of the collarbone
• Pain may feel widespread throughout the shoulder initially; as the pain settles, it becomes more localised over the joint
• Swelling is common
• Depending on the severity of the injury, a step deformity may be visible—this is a noticeable lump where the joint has been disrupted and is more pronounced in severe injuries
• Pain with shoulder movement, especially when trying to raise the arms above shoulder height or across the body

There are various grading scales for AC Joint injuries as shown below:

Grade 1 (mild)
Tenderness and discomfort on palpation and movement. Partial damage to the joint capsule and AC ligament. Usually no visible bump. Return to play – up to 3 weeks.

Grade 2 (moderate)
Complete rupture of the acromioclavicular ligament and partial tear of the coracoclavicular ligament. This allows the clavicle to move upward, creating a visible bump. Pain is more severe and shoulder movement is restricted. Return to play – minimum 4 to 6 weeks.

Grade 3 (severe)
Complete rupture of both the acromioclavicular and coracoclavicular ligaments. The bump is more pronounced due to complete dislocation of the AC joint. Return to play – dependent on management (e.g. surgery).

Management

Initial treatment of soft tissue injuries should follow the RICER protocol – Rest, Ice, Compression, Elevation and Referral. This should be applied for 48–72 hours to reduce bleeding and damage within the joint. The shoulder should be rested in a sling, and an ice pack applied for 20 minutes every two hours (never apply ice directly to the skin). This may be necessary for as little as two days in mild injuries or up to three weeks in more severe cases.

The No HARM protocol should also be followed – No Heat, No Alcohol, No Running or activity, and No Massage – to reduce swelling and internal bleeding.

A sports medicine professional should be consulted as soon as possible to assess the injury and advise on appropriate treatment. Assessment may include a physical examination and x-rays of the shoulder.

Most AC joint injuries are managed conservatively with a period of immobilisation followed by a rehabilitation program involving strengthening exercises, once pain allows. Surgery is generally reserved for cases involving complete joint dislocation (Grade 3) or where conservative management is unsuccessful.

Most patients can return to their chosen sport following appropriate rehabilitation.

Ways to help prevent and AC joint injury include:

• Wearing protective strapping to support a previously injured AC joint, particularly in contact sports or sports where full elevation of the arm is not essential. Protective padding is also used in sports such as rugby
• Warming up, stretching and cooling down
• Participating in fitness programs to develop strength, balance, coordination and flexibility
• Undertaking training prior to competition to ensure readiness to play
• Gradually increasing the intensity and duration of training
• Allowing adequate recovery time between workouts or training sessions
• Wearing the right protective equipment, including appropriate footwear
• Checking the sporting environment for hazards prior to training and match play
• Avoiding activities that cause pain. If pain occurs, discontinue the activity immediately and commence RICER