The AC joint is located at the top of the shoulder and is the joint that connects the outer end of your collarbone (clavicle) to the shoulder blade (acromion). There are important ligaments that hold the collarbone to the shoulder blade called the coracoclavicular ligaments. Both these ligaments and the AC joint itself can be injured when falling on your shoulder.
What are the causes?
ACJ injury occurs due to a traumatic event where direct force is applied to the joint. It is commonly seen in people who have fallen off their bicycle or rugby players as both sports commonly cause impact to the ACJ.
What are the symptoms?
ACJ injury causes pain specifically over the joint itself localised at the outer end of the collarbone. If the pain is felt elsewhere then this may be due a different cause such as a rotator cuff tear.
The joint can dislocate due to rupture of the coracoclavicular (CC) ligaments. The end of the collarbone will become much more pronounced. This can be associated with a feeling of weakness in the arm, particularly when carrying heavy items.
How is it diagnosed?
Your surgeon can usually make the diagnosis by asking about the symptoms you have and examining your shoulder. An X-ray will confirm the diagnosis.
How is it treated?
If you have suffered an ACJ sprain, symptoms should settle with rest and physiotherapy with or without an injection. If symptoms persist then surgery in the form of ACJ excision can be done.
Symptoms from a dislocated ACJ can also settle although the appearance of the joint will remain the same. If symptoms don’t settle an operation to reconstruct the ligaments can be performed called a coracoclavicular ligament reconstruction.
Coracoclavicular ligament reconstruction