An AC joint dislocation, commonly referred to as a shoulder separation, is not truly an injury to the shoulder joint. The injury actually involves the acromioclavicular joint (also called the AC joint). The AC joint is where the collarbone (clavicle) meets the highest point of the shoulder blade (acromion). An AC separation is when the clavicle “separates” from it’s normal position adjacent to the acromion.
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. This creates a bump or bulge on the top of the shoulder.
The injury can range from a mild sprain without a bump to a complete tearing of the stabilizing ligaments with a very large bump. Typically, these large bumps above the shoulder are permanent, if left untreated.
- 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 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 above the shoulder.
AC joint dislocations can be diagnosed with an x-ray of the affected shoulder compared with the unaffected shoulder.
This figure shows the intact ligaments around the AC joint. The red arrow points to the ligaments that are around the joint itself (AC ligaments). The gray arrow points out the important stabilizing ligaments, the coracoclavicular (CC) ligaments, underneath the collarbone.
Most AC separations are treated nonsurgically. A sling, ice, and anti-inflammatory medication can often help manage the pain. Sometimes, physical therapy is necessary to rehabilitate your shoulder.
Most people return to near full function with this injury, but it’s possible there may be a persistent bump on the top of the shoulder. Some people may have continued pain in the area of the AC joint, which may be due to abnormal contact between the bone ends when the joint is in motion, or development of arthritis.
Surgery can be considered if pain persists or the deformity is severe, to restore normal alignment to the AC joint. Where there is significant deformity, reconstructing the ligaments that attach to the underside of the collarbone may be considered. When surgery is necessary, it is helpful to address these injuries within 6 weeks of the injury date, but this procedure can be performed even if a period of time longer than 6 weeks has passed. These operations are typically done through an open approach with assistance from an arthroscope.
Whether treated conservatively or with surgery, the shoulder will require rehabilitation to restore and rebuild motion, strength, and flexibility.