An acromioclavicular (AC) joint sprain is a common injury, particularly among active people involved in contact sports or those who suffer falls. This injury occurs at the AC joint, which is the connection point between the shoulder blade and the collarbone. A sprain involves the stretching or tearing of the ligaments that stabilize this joint. The severity of the damage can range from a mild stretch to a complete tear of the connective tissues, making it a spectrum of injury with different implications for recovery.
The Anatomy of the Acromioclavicular Joint and Sprains
The AC joint is formed by the lateral end of the clavicle, or collarbone, and the acromion, which is the outermost part of the shoulder blade. This joint is primarily held in place by two sets of ligaments. The acromioclavicular (AC) ligaments surround the joint capsule, controlling horizontal stability.
The second set, known as the coracoclavicular (CC) ligaments, are composed of the trapezoid and conoid ligaments, and they provide the main vertical stability. These CC ligaments connect the clavicle to the coracoid process, effectively suspending the arm from the collarbone.
The most common way this injury happens is through a direct, forceful blow to the tip of the shoulder, such as falling onto the shoulder while the arm is tucked close to the body. This impact drives the acromion downward, forcing the AC joint apart and subjecting the stabilizing ligaments to extreme stress. The force can also be transmitted indirectly by falling onto an outstretched hand, pushing the arm up into the joint.
Recognizing the Signs and Symptoms
Patients typically feel immediate, localized pain right at the top of the shoulder, often directly over the joint where the clavicle and acromion meet. The injured area will likely be tender to the touch, and swelling and bruising are common signs observed shortly after the trauma.
Movement of the arm is often restricted and painful, especially when attempting to lift the arm above shoulder height or reaching across the body. In more significant cases, a visible bump or “step deformity” may appear on the top of the shoulder. This deformity occurs when the collarbone end becomes prominent due to the loss of ligamentous support.
Understanding Injury Grading and Diagnosis
A medical professional begins the diagnosis with a physical examination, assessing the range of motion and checking for tenderness directly over the AC joint. Specific stress tests, such as the AC joint compression test, are performed to evaluate the joint’s stability and identify the precise source of the pain. The definitive diagnosis and classification rely on imaging, typically using X-rays to rule out fractures and visualize any displacement of the clavicle relative to the acromion.
AC joint sprains are classified using a system that ranges from Type I to Type VI, based on the extent of ligament damage and the degree of clavicular displacement. A Type I sprain is the mildest, involving only a stretch of the AC ligaments with no tearing and no visible displacement of the joint.
Type II falls between these two, involving a complete tear of the AC ligament but only a partial tear or sprain of the stronger CC ligaments, leading to a slight misalignment of the joint. A Type III sprain represents a complete tear of both the AC and CC ligaments, resulting in a noticeable superior displacement of the clavicle. Higher grades, Type IV through VI, involve increasingly severe displacement or dislocation, often requiring specialized imaging for full assessment.
Treatment Pathways and Recovery Timelines
The treatment approach for an AC joint sprain is directly guided by the injury grade, with most lower-grade sprains managed without surgery. Non-surgical management, often recommended for Type I, II, and sometimes Type III injuries, typically follows the RICE protocol: rest, ice application, and temporary immobilization in a sling for comfort and support. Over-the-counter or prescription pain medication helps manage discomfort and swelling during the initial healing phase.
Physical therapy is a fundamental component of recovery once the initial pain subsides. Therapy focuses on restoring the full range of motion and strengthening the surrounding shoulder muscles.
Recovery timelines vary significantly by grade. For a mild Type I sprain, recovery is generally swift, often taking only one to two weeks before a return to normal activity is possible. A moderate Type II sprain typically requires a longer period of three to six weeks for healing and rehabilitation.
For a complete tear, such as a Type III sprain, non-surgical recovery can take between six and twelve weeks, with soft tissue pain sometimes lingering for up to three months. Surgical intervention is generally reserved for the more severe, high-grade injuries (Type IV, V, and VI). Surgery may also be necessary for cases of Type III sprains in highly active individuals where non-operative treatment fails to restore function. When surgery is performed to stabilize the joint, the full recovery timeline, including rehabilitation, can extend to four to six months.