What is an AC joint shoulder injury?
The acromioclavicular joint (AC joint) is where the collarbone (clavicle) meets the highest point of the shoulder blade (acromion). The joint is held together by three strong ligaments and possesses cartilage that covers the ends of both bones. An injury to the AC joint can result in a sprain of these ligaments or a shoulder separation. Boulder, Colorado, orthopedic shoulder and sports medicine specialist, Dr. Austin Chen specializes in treating AC joint injuries.
Shoulder separations occur on a spectrum ranging from a sprain or partial tear (Grade I) of the ligaments, to complete tearing of all major ligaments that support the joint (Grade IV).
- Grade I: Sprain of the joint without complete tear of either ligament
- Grade II: Tear of AC ligament. Coracoclavicular (CC) ligament intact. No elevation of lateral end of clavicle
- Grade III: Tear of AC ligament and CC ligament. >5mm elevation of lateral clavicle.
- Grade IV: Tear of AC ligament and CC ligament. Elevation and Posterior displacement of clavicle into trapezius muscle.
What is the cause of a AC joint injury?
The most common cause for a separation of the AC joint is from a fall directly onto the shoulder. The fall injures the ligaments that surround and stabilize the AC joint. If the force is severe enough, the ligaments attaching to the underside of the clavicle are torn. This causes the separation of the collarbone and the shoulder blade. The shoulder blade (scapula) actually moves downward from the weight of the arm. This creates a bump or bulge above the shoulder.
The AC joint injury can range from a mild sprain without a bump to a complete disruption with a very large bump. Good pain-free function often returns even with a very large bump. The greater the deformity, the longer it takes for pain-free function to return.
- A mild shoulder separation involves a sprain of the AC ligament that does not move the collarbone and looks normal on X-rays.
- A more serious injury tears the AC ligament and sprains or slightly tears the coracoclavicular (CC) ligament, putting the collarbone out of alignment to some extent with a smaller bump.
- The most severe shoulder separation completely tears both the AC and CC ligaments and puts the AC joint noticeably out of position, with a larger bump.
What are the symptoms of a AC joint injury?
Symptoms of an injured AC joint range from tenderness and mild swelling, to severe pain and a prominent visual bump protruding from the top of the shoulder.
What is the treatment for a AC joint injury?
Nonsurgical treatment for an AC joint injury include a sling, cold packs, and medications to manage the pain. Most people return to near full function with this injury, even if there is a persistent, significant deformity/bump. Some people have continued pain in the area of the AC joint, even with only a mild deformity.
This may be due to:
- Abnormal contact between the bone ends when the joint is in motion
- Development of arthritis
- Injury to a disk-like piece of cushioning cartilage that is often found between the bone ends of this joint
For more severe injuries, shoulder instability and susceptibility to future separations and dislocations, Dr. Chen may suggest surgery. Numerous surgical techniques are available to repair and stabilize the joint. Minimally invasive arthroscopic surgery is often used to return the joint to its proper position, repairing any damaged structures and re-establish a full range of motion.
