The acromioclavicular (AC) joint connects the clavicle (collarbone) to the highest point of the shoulder blade, the acromion. A direct blow to the shoulder, such as from a fall, can damage the stabilizing ligaments, leading to a shoulder separation. When these ligaments are injured, the outer end of the clavicle shifts upward, creating a noticeable protrusion on the top of the shoulder referred to as an AC joint “bump.” This prominence is a structural displacement of the bone, not just swelling, and its management depends on the severity of the underlying ligament damage.
Understanding the AC Joint Bump’s Formation
The AC joint is stabilized by two sets of ligaments: the acromioclavicular (AC) ligaments, which span the joint, and the stronger coracoclavicular (CC) ligaments, which connect the clavicle to the coracoid process of the shoulder blade. An injury that drives the shoulder blade downward can stretch or tear these ligaments. The resulting bump occurs when the lateral end of the clavicle shifts upward because the CC ligaments, which normally tether the clavicle down, are no longer intact.
The severity of the injury is classified using a six-grade system, with the visible bump typically appearing in Grade II and higher separations. A Grade II injury involves a complete tear of the AC ligaments and a partial tear of the CC ligaments, causing slight upward displacement. In a Grade III separation, both ligament sets are completely torn, allowing the clavicle to elevate significantly and creating a more pronounced prominence. Grades IV through VI involve even greater displacement and tearing of surrounding muscle attachments.
Conservative Management and Functional Restoration
For the majority of AC joint injuries, including Grade I, II, and often Grade III separations, the initial approach involves conservative management. This strategy focuses on immediate pain control and protecting the joint while the ligaments heal. Initial care includes a brief period of rest, using a sling to immobilize the arm, and applying ice to minimize pain and swelling.
Once the initial pain subsides, typically after several weeks, the focus shifts to a structured physical therapy program. Rehabilitation targets regaining the shoulder’s full range of motion, followed by strengthening the surrounding musculature, particularly the deltoid and trapezius muscles. Strengthening these muscles helps create dynamic stability, compensating for the damaged static ligament structures.
Conservative management is highly effective at restoring full strength and painless range of motion, but it does not physically eliminate the bony prominence. The clavicle remains in its elevated position, stabilized by scar tissue and surrounding muscles. The goal is to achieve a stable, functional shoulder despite the residual bump.
Surgical Procedures for Correcting the Prominence
Surgical intervention is generally reserved for high-grade injuries (Grades IV, V, and VI), cases where conservative treatment failed to restore adequate function, or when the cosmetic deformity is a significant concern. The primary goal of surgery is to reduce the clavicle back into its anatomical position and stabilize it. This allows torn ligaments to heal or facilitates the reconstruction of damaged structures, offering the only definitive way to address the prominence.
A common modern technique is coracoclavicular ligament reconstruction. This is often performed using high-strength suture materials secured with titanium buttons or a suture button system, passed through tunnels drilled in the clavicle and coracoid process. This method pulls the clavicle down, holding it in place while natural ligaments heal or while a tendon graft integrates. For chronic injuries, where ligaments cannot be repaired, a tissue graft is necessary to recreate the missing CC ligament structure.
Another procedure, known as a distal clavicle excision (Mumford procedure), involves removing a small piece of the lateral end of the clavicle. This procedure is not a primary reduction technique for the bump but relieves chronic pain caused by arthritis or bony impingement. While not intended to correct the height, removing the bone end may result in a less noticeable prominence. Even with surgical reduction and stabilization, patients should be aware that some minor residual prominence can still remain post-operatively.