ACJ stands for acromioclavicular (AC) joint, which is where your collarbone (clavicle) joins your shoulder blade at the acromion. The AC joint allows you to move your arm above your head and across your body and is used in pushing, pulling and lifting movements.
An ACJ injury – also called a shoulder separation – occurs when the acromion in the shoulder blade and the collarbone are forced apart, causing the ligaments supporting the joint to become overstretched and damaged in the process. Damage can range from a mild strain affecting one or more ligaments to a complete ligament tear.
ACJ injuries or dislocations are normally caused by a fall – such as falling off a bike or landing badly on your shoulder during a tackle – or a direct impact with an object or surface with your shoulder. Less commonly if you fall onto your outstretched arm, the force can be transmitted up your arm causing an ACJ injury.
The symptoms of an ACJ injury include:
- Pain at the top of the shoulder which is aggravated by heavy lifting and moving your arm across your body
- A hard lump at the top of the shoulder caused by displacement of the collarbone
- Loss of shoulder movement
This type of injury is normally diagnosed with both physical examination and an X-ray to establish whether any of the bones are fractured. During the X-ray you may be asked to hold a weight in your hand to show the severity of the injury more clearly.
Initially, we recommend resting the injured area, using ice packs to bring down swelling and taking anti-inflammatory medication to reduce inflammation. Physiotherapy can help to improve the range of motion, strength and alignment of your shoulder and shoulder blade.
In severe cases you may need ACJ reconstruction surgery to stabilise the AC joint and/or repair the damaged ligaments. A rehabilitation programme will be needed following surgery to restore the full range of movement to your shoulder. In rare cases, a degree of instability and stiffness may persist. Your consultant will discuss the full range of possible operations, risks and complications with you.