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.
