An acromioclavicular (AC) separation is a common shoulder injury, which is distinct from a shoulder dislocation. This injury occurs at the AC joint, the point where the collarbone (clavicle) meets the highest part of the shoulder blade (acromion). The separation involves damage to the ligaments that stabilize this joint, causing the clavicle to shift position relative to the acromion.
The Anatomy of the AC Joint and How Separation Occurs
The AC joint is a gliding joint that connects the shoulder girdle to the rest of the skeleton, allowing the arm to move. Two main groups of ligaments provide stability to this junction. The acromioclavicular (AC) ligaments surround the joint capsule, controlling horizontal motion and anterior-posterior stability.
The coracoclavicular (CC) ligaments, which include the conoid and trapezoid ligaments, provide vertical stability by preventing the clavicle from migrating upward. These ligaments span the distance between the clavicle and the coracoid process, a bony projection on the shoulder blade. An AC separation most commonly happens when a person falls directly onto the point of the shoulder. This direct force drives the acromion downward, stretching or tearing the AC and CC ligaments and causing the clavicle to separate from the acromion.
Grading the Injury Severity
The injury severity is classified using a system based on the extent of ligament disruption and the degree of clavicle displacement. A Grade I separation is the least severe, involving only a mild stretching or sprain of the AC ligaments, with the CC ligaments remaining intact and no visible displacement of the clavicle. Patients experience minimal pain and swelling.
A Grade II injury means the AC ligaments are completely torn, but the CC ligaments are only sprained or partially torn. This results in a slight, partial displacement of the clavicle, which may be noticeable as a small bump on the shoulder. Grade III is a complete separation where both the AC and the CC ligaments are fully torn, causing the clavicle to be significantly displaced upward and creating a prominent deformity.
The classification system includes three more severe, but much rarer, types: Grades IV, V, and VI. These all involve complete tears of both ligament groups and extensive soft tissue damage. A Grade IV injury is characterized by the clavicle being displaced backward (posteriorly) into the trapezius muscle. Grade V involves extreme upward displacement of the clavicle. A Grade VI separation is extremely rare and involves the clavicle being displaced downward (inferiorly) and lodged beneath the coracoid process.
Conservative Treatment Options
Conservative treatment is the standard approach for most AC separations, including Grades I, II, and often Grade III cases. The initial focus is on symptom management, involving rest and the application of ice to reduce pain and swelling at the joint. Pain medication, such as non-steroidal anti-inflammatory drugs (NSAIDs), is often used to manage discomfort.
A sling is commonly used for temporary immobilization to support the arm and reduce tension on the injured joint. For a Grade I injury, the sling may only be needed for a few days, while a Grade II injury might require up to a week or more. The goal of conservative care is to restore full function, though a slight bump may remain after healing, especially in Grade II and III injuries.
Physical therapy begins once the initial pain subsides, starting with gentle, passive range-of-motion exercises to prevent stiffness. The rehabilitation program progresses to active-assisted motion and then strengthening exercises, focusing on the muscles surrounding the shoulder blade and the rotator cuff. This process restores dynamic stability to the shoulder complex for a successful return to activity.
When Surgery Is Required and the Road to Recovery
Surgical intervention is reserved for the most severe AC separations, primarily Grades IV, V, and VI. Surgery may also be considered for certain Grade III injuries, particularly in younger, highly active individuals, overhead athletes, or manual laborers who require maximum shoulder function. The procedure’s goal is to restore the correct anatomical relationship by stabilizing the clavicle back to the acromion and coracoid process.
Stabilization is achieved by surgically reconstructing the torn CC ligaments, often using high-strength sutures, specialized devices, or tendon grafts to hold the bones in place while the body heals. Recovery involves a period of post-operative immobilization, often in a sling for about four weeks. The patient then transitions into an intensive physical therapy program.
Rehabilitation progresses from controlled, early motion to strength training, with limitations on overhead movement often lasting for several weeks. For surgical patients, the full recovery timeline and return to unrestricted activities, such as contact sports or heavy manual labor, typically ranges between four to six months. Delayed surgical reconstruction may be considered if a non-operative Grade III injury causes persistent pain or dysfunction after two to three months.