Acromioclavicular Joint Separation
The bones that make up the shoulder are the upper end of the arm bone (humerus), the shoulder blade (scapula), and the collarbone (clavicle). Some would describe this joint as a ball and socket joint, but, it is more like a ball sitting on a golf tee, meaning that there is a tiny surface area of bone contact. The stability of the shoulder joint relies heavily on the soft tissues around the bone, including muscles, tendons, capsule, and labrum, that keep the arm centered with the shoulder blade. The collarbone or clavicle is another structure in the shoulder region that attaches to the shoulder blade at the front of the shoulder; this joint is called the acromioclavicular joint (AC joint).
Also called a shoulder separation, an acromioclavicular joint separation is where the clavicle is traumatically pulled away from the highest point of the shoulder blade, called the acromion.
Mechanism of Injury
These injuries usually occur due to a direct, forceful blow to the shoulder or falling directly onto the shoulder. These are also called shoulder separation injuries, where the damage disrupts the soft tissues that hold the bones together; these are known as ligaments. These injuries can also occur concomitantly with a fracture, typically a clavicle fracture. In mild cases, there may be no change or only minimal changes in the position of the bones. In more complex issues with multiple ligaments torn around the joint, the clavicle will appear higher, and the shoulder will pull down due to the arm’s weight. There may be a noticeable bump and the front of the shoulder where the clavicle meets the shoulder blade.
Physical examination and x-ray imaging are generally used to diagnose this condition. On x-ray, the space between the clavicle and the part of the shoulder blade that meets the acromion is evaluated. The amount of upward movement of the clavicle is also noted.
Additional imaging is sometimes ordered, including CT scans and MRIs.
Mild injuries may appear normal on imaging but have symptoms such as pain directly over the joint. This would be considered a sprain or partial tearing of the ligaments.
The severity of the injury increases as more structures are damaged and there is more displacement or separation between the bones.
In rare cases, the clavicle may be inferiorly displaced, meaning the collarbone is below the acromion. This will typically require surgery to reduce or put back into a normal position.
Most cases of AC joint separation can be treated well without surgery. There may be a period of immobilization or resting the shoulder joint, followed by exercises or physical therapy designed to regain the strength of the shoulder and arm. Recent studies show that patients with higher-grade injuries have about the same functional result whether the injury was treated with or without surgery.
Surgery may benefit patients with high-grade injuries with high demand, such as athletes, or with cosmetic concerns. Surgery is also an option for patients who do not recover well from more conservative forms of treatment. Surgery may involve using sutures, screws, wires, or plates to reconstruct the joint. They may be performed in a minimally invasive fashion using cameras, called arthroscopy, or in an open manner where the surgeon will make an incision over the joint, then move the bones to a better position and apply sutures or hardware.
Complications of AC joint separation may include arthritis or joint instability.