Acromioclavicular Joint Problems
What is the acromioclavicular joint?
Often referred to as the ACJ, the acromioclavicular joint is the point where the collar bone (clavicle) meets the flat bone at the top of the shoulder blade, known as the acromion. The joint is located on the tip of the shoulder and moves when your arm is overhead or stretching across your chest. The ACJ is held in position by two ligaments (the coracoclavicular ligaments) and cushioned by a thick pad of cartilage, known as the meniscus.
What are the common acromioclavicular joint problems?
The three most common conditions that can affect the acromioclavicular joint are arthritis, stress fractures (osteolysis) and dislocations.
- ACJ arthritis is a degenerative disease that can cause a loss of cartilage around the joint. This can lead to irritation, the development of bony spurs, inflammation and pain around the joint.
- Stress fractures of the ACJ (also known as ACJ osteolysis) can happen at the outer end of the collar bone, at the point where it joins the shoulder blade.
- The acromioclavicular joint can dislocate, just like the shoulder can. It normally happens due to a traumatic injury which causes the ligaments holding the bones of the joint in place to break.
Why do acromioclavicular joint problems happen?
The most common cause of acromioclavicular joint arthritis is wear and tear through over use. For this reason it is most common in people who are aged 50 or older and in athletes who place a lot of stress on the joint – such as rugby players and weight lifters.
The acromioclavicular joint can be dislocated by trauma such a fall directly onto the tip of the shoulder, or by a fall onto an outstretched hand. The degree of dislocation is determined by how many of the ligaments are torn and how far the collar bone has been moved. The severity of the injury can be graded from I-VI
Grade I injury
This involves damage to the joint itself with a ‘sprain’ of the capsule. The lateral end of the clavicle is not displaced and other than some swelling at the time of injury there is no cosmetic deformity
A Grade II injury is a partial dislocation of the ACJ with disruption to the joint and possibly damage to the intra-articular meniscus
A Grade III injury involves complete separation of the ACJ. The Conoid and trapezoid (coracoclavicular) ligaments are damages and the end of the clavicle dislocates upwards with a cosmetic deformity
ACJ stress fractures
Repetitive overhead activities that put an excessive weight on the edge of the collar bone can lead to erosion or stress fractures (osteolysis). ACJ stress fractures are most commonly seen in athletes such as rugby players
and weightlifters and in people whose work includes heavy overhead activities, such as builders and plasterers.
How common are acromioclavicular joint problems?
Acromioclavicular joint injuries are most common in athletes who have to carry weight on their shoulders, such as weightlifters, wrestlers and rugby players. This type of injury is also more common in builders and plasterers, who may carry weights overhead, and in older people who may suffer from additional wear and tear and arthritic change to their joints.