The acromioclavicular (AC) joint connects the collarbone (clavicle) to the shoulder blade (scapula) at the top of the shoulder. An “AC joint bump” refers to a visible prominence or swelling that can appear in this area following an injury. This prominence often results from damage to the ligaments supporting the AC joint. This article explores the nature of AC joint injuries, factors influencing the persistence of a shoulder bump, and available management strategies.
Understanding the AC Joint and Its Injuries
The AC joint is located at the top of the shoulder, forming the articulation between the distal end of the clavicle and the acromion process of the scapula. It is stabilized by several ligaments, including the acromioclavicular (AC) ligaments and the coracoclavicular (CC) ligaments. Injuries to the AC joint commonly result from a direct blow to the top of the shoulder, such as falling directly onto the shoulder or being tackled in sports.
This impact can cause the acromion to be driven downwards, straining or tearing these stabilizing ligaments. When these ligaments are stretched or torn, the clavicle can separate from the acromion, leading to an “AC joint separation.” These separations are classified into grades based on the severity of ligamentous damage and the degree of clavicle displacement. Lower grades involve less significant ligament damage and minimal displacement, while higher grades indicate complete tears and more pronounced separation. The visible bump that often forms after an AC joint injury is a direct consequence of this displacement or associated swelling.
Factors Influencing Bump Persistence
The persistence of an AC joint bump is largely determined by the specific grade of the acromioclavicular separation. Lower-grade injuries, such as Grade I and Grade II separations, typically involve sprains or partial tears of the AC ligaments. In Grade I injuries, ligaments are stretched but not torn, while Grade II injuries show some partial tearing and slight displacement.
For these lower grades, any initial bump is often due to localized swelling and inflammation rather than significant bone displacement. As swelling subsides and ligaments heal, the bump usually diminishes considerably or resolves entirely over several weeks to a few months. The shoulder contour generally returns close to its pre-injury state.
Conversely, Grade III and higher AC joint separations involve more extensive damage to the supporting ligaments. A Grade III injury signifies a complete tear of both the AC and CC ligaments, leading to a noticeable upward displacement of the clavicle. In these cases, the clavicle loses its primary anchors, causing it to elevate and create a prominent, often permanent, visible bump.
For higher-grade injuries, the bump typically does not “go away” on its own because the complete ligamentous disruption prevents the clavicle from returning to its original anatomical position. While the bump may become slightly less prominent over time as initial swelling resolves, the bony protrusion usually remains a permanent feature.
Management and Treatment Approaches
The management of an AC joint injury depends on its grade, the patient’s activity level, and symptoms. Non-surgical approaches are the primary treatment for most AC joint separations, especially Grades I, II, and often Grade III. Initial non-surgical management involves rest, ice to reduce swelling, and pain medication.
A sling may be used for a short period, typically one to three weeks, to immobilize the shoulder and aid healing. Physical therapy is an important component of recovery, focusing on restoring range of motion, strengthening shoulder muscles, and improving overall shoulder function. These conservative treatments aim to alleviate pain, reduce inflammation, and facilitate healing, allowing most individuals to regain full shoulder function.
Surgical intervention is considered for higher-grade AC joint separations, particularly Grade III in highly active individuals, or Grades IV, V, and VI. Surgery may also be an option for patients with persistent pain, significant functional limitations, or cosmetic concerns not resolved with non-surgical management. The goal of surgery is to stabilize the AC joint by realigning the clavicle and repairing torn ligaments.
While surgical repair can reduce the bump’s prominence, it does not always guarantee its complete disappearance. The decision to pursue surgery involves weighing potential benefits against risks and recovery time.
Life After an AC Joint Injury
Most individuals who sustain an AC joint injury can expect a good functional recovery, regardless of whether a visible bump persists. The recovery timeline varies significantly based on the injury’s grade; lower-grade injuries typically allow a return to activities within a few weeks to two months, while higher grades may require several months of rehabilitation. Even with a persistent bump, many people regain full range of motion and strength, enabling them to return to their previous activity levels, including sports.
Long-term outcomes are generally favorable, with the primary goal being the restoration of pain-free shoulder function. However, some individuals may experience chronic issues such as persistent localized pain at the AC joint, especially with direct pressure or overhead activities. There is also an increased risk of developing post-traumatic arthritis in the AC joint over time, which can lead to stiffness and discomfort.
Cosmetic concerns regarding the visible bump can also be a long-term consideration for some individuals. It is important to consult a healthcare professional for an accurate diagnosis and a personalized treatment plan, especially if new or worsening symptoms develop after the initial injury.