The acromioclavicular joint, also known as the AC joint, is located at the top of the shoulder where the clavicle (collar bone) and the acromion of the scapula (shoulder blade) meet. The AC Joint capsule and ligaments surrounding the joint work together to provide it with stability.
The primary function of the AC joint is:
To allow for additional movement of the scapula on the thorax (chest).
To allow the scapula to adjust its position (by tipping or rotating) following the change in shape of the thorax as the arm moves
Allows for forces from the upper extremity to transmit through to the clavicle
Common causes of AC joint pain
Dislocation: An acromioclavicular dislocation is a traumatic dislocation of the joint in which the clavicle gets displaced in relation to the shoulder. Commonly, this happens when falling onto an outstretched hand or elbow, direct blows to the shoulder, or falling onto the point of the shoulder.
Osteoarthritis : Also known as the “wear and tear” arthritis; destroys the articular cartilage resulting in inflammation. As the cartilage wears away and becomes frayed and rough, protective space between the bones decreases.
Overuse : Pain in the AC joint is mostly caused by the overuse of the shoulder. It is quite common between gym goers and body builders. Frequent bench pressing and other heavy lifting activities can lead to inflammation.
Symptoms
Pain is often felt when:
Reaching overhead causing sharp pain on the top of your shoulder
Reaching across your body in front of you,
Pressure is placed over the joint.
AC Joint injuries often radiate into the neck and shoulder. The joint may also become swollen, with the arm held close to the body and acromion depressed, which may cause the clavicle to be elevated.
Management
Treating an AC joint injury will vary depending on its severity. Severity can be classified based on the table shown above. For type I and type II AC joint separation, nonoperative treatment is usually recommended, whereas surgical repair is recommended for type IV and V.
Conservative Management
When managed conservatively, treatment should initially follow the PEACE and LOVE protocol (check out the details in our previous blog). Sometimes a sling may also be used to immobilise the shoulder and maintain it in an elevated position when resting.
Recovery time
For type I injuries, normal activities can usually be resumed in 2-4 weeks. Type II usually takes 4-6 weeks, and 6-12 weeks for type III.
Exercise
Exercise is an important part of the recovery process, whether managed conservatively or surgically. Once initial swelling and pain settles, exercises should be started. Below are some example exercises and how it progresses through a structured rehab program.
Range of motion - aimed at restoring the normal movement of the shoulder
Exercise: active assisted shoulder flexion - the non-injured side is used to assist the injured side with a dowel
Stability - aimed at improving the ability to maintain the upper arm within the centre of the joint and allow the scapula to move properly
Exercise: shoulder stability with ball - weight is put into the ball against the wall while performing up and down movements, while trying to maintain the shoulder and scapula in the correct position
Strength - to improve the physical capacity of the muscles around the shoulder joint to further improve the stability, assist with movements of the shoulder and prevent further injuries and complications
Exercise: single arm row - aimed at strengthening the muscles around the shoulder and upper back
This blog provides an introduction to the AC joint of the shoulder, common causes of pain, and management. Following injury it is important to seek proper medical advice from a physiotherapist, GP or other health professionals. If you are experiencing shoulder pain, book in a session with us for a thorough assessment and tailored plan to get you better.
References
Beim, G. M. (2000). Acromioclavicular joint injuries. Journal of athletic training, 35(3), 261.
Images obtained from Physitrack
Saccomanno MF. Acromioclavicular joint instability: anatomy, biomechanics and evaluation. Joints 2014; 2(2): 87–92.