An acromioclavicular (AC) separation is a common injury affecting the shoulder joint where the collarbone meets the shoulder blade. Often called a shoulder separation, it involves damage to the acromioclavicular joint, which connects the clavicle (collarbone) to the acromion (the highest part of the scapula or shoulder blade). This injury should not be confused with a shoulder dislocation, which affects the main ball-and-socket joint.
Understanding the AC Joint and Injury Causes
The acromioclavicular joint is a small, gliding joint stabilized by a complex network of ligaments that prevent excessive movement. Primary support comes from two distinct sets: the acromioclavicular (AC) ligaments and the coracoclavicular (CC) ligaments. The AC ligaments surround the joint capsule, providing horizontal stability and preventing the clavicle from moving relative to the acromion.
The CC ligaments, composed of the trapezoid and conoid ligaments, connect the clavicle to the coracoid process on the shoulder blade. These ligaments are responsible for the joint’s vertical stability, preventing the clavicle from riding up above the acromion. Injury is most frequently caused by a forceful, direct blow to the point of the shoulder, often during a fall onto the shoulder when the arm is tucked close to the body.
This mechanism drives the acromion downward while the clavicle remains in place, forcing the ligaments to stretch or tear. Injuries may also occur from a fall onto an outstretched hand, though this is less common. The resulting pain, swelling, and possible visible bump at the top of the shoulder are consequences of the damaged ligaments and the instability of the clavicle.
The Grading System for AC Separations
AC separations are classified using the Rockwood classification system, which categorizes the injury into six types based on the severity of ligament damage and the degree of clavicle displacement. This grading helps determine the appropriate course of treatment. The most common injuries are Grades I, II, and III, which represent a sequential increase in damage to the supporting structures.
A Grade I separation is the mildest form, involving only a sprain or stretch of the AC ligaments without significant tearing or joint displacement. The clavicle remains in its correct position, and symptoms are limited to localized pain and tenderness. A Grade II injury involves a complete tear of the AC ligaments, but the deeper CC ligaments remain intact, though they may be stretched. This damage results in a partial separation and a slight, noticeable upward displacement of the clavicle.
A Grade III separation represents a complete disruption of both the AC and CC ligaments, leading to a definite, visible superior displacement of the clavicle. The distance between the coracoid process and the clavicle is increased by 25% to 100% compared to the uninjured shoulder. Grades IV, V, and VI are rare, severe injuries that involve complex displacement of the clavicle, often requiring specialized surgical planning. Grade V is a gross separation where the clavicle is markedly displaced upward, tearing through muscle attachments.
Treatment Approaches Based on Severity
The chosen treatment pathway for an AC separation depends directly on its Rockwood classification grade. Grades I and II separations are typically managed non-operatively, focusing on pain management and protection of the injured joint. Treatment includes a short period of rest, application of ice to reduce swelling, and the use of a sling for comfort and temporary immobilization for up to a few weeks.
The decision for Grade III injuries is often patient-specific, considering factors such as age, occupation, and athletic demands. Many Grade III injuries are successfully treated non-operatively with rest and rehabilitation. However, athletes involved in overhead or contact sports, or individuals who perform heavy manual labor, may benefit from surgery. Long-term studies suggest non-operative management often yields comparable functional results to surgery after one year, though a noticeable bump may persist.
Surgical intervention is generally reserved for high-grade separations (Grades IV, V, and VI) due to significant displacement and disruption of surrounding soft tissues. The primary goal of surgery is to anatomically realign the clavicle with the acromion and restore the stability provided by the torn CC ligaments. Techniques often involve strong sutures or grafts to reconstruct the ligaments and temporarily fix the joint with plates or screws while soft tissues heal.
Rehabilitation and Long-Term Recovery
Recovery from an AC separation is a phased process that varies based on the injury’s grade and whether surgery was performed. For non-operative Grade I and II injuries, a return to full activity is typically expected within two to six weeks, starting with gentle range-of-motion exercises once pain subsides. Grade III separations treated non-surgically may require up to 12 weeks before a return to full, unrestricted activity.
Physical therapy is a structured progression that begins with passive and active-assisted range of motion exercises to prevent stiffness. Once motion is regained without pain, the focus shifts to strengthening the muscles surrounding the shoulder blade, including the rotator cuff and scapular stabilizers. This strengthening phase is crucial for providing dynamic stability to the joint, compensating for any residual ligamentous laxity.
Following surgical fixation for higher-grade injuries, the recovery timeline is considerably longer, often requiring four to six months before a full return to contact sports or heavy lifting. The rehabilitation program is more protected initially, involving longer immobilization. However, it follows the same sequence of restoring motion before progressing to focused strengthening. Full function, even after the most severe separations, is the expected outcome for most individuals who commit to a comprehensive rehabilitation plan.