The acromioclavicular (AC) joint, located in the shoulder, can be torn. These common injuries are often referred to as “shoulder separations” or “AC joint sprains.” The AC joint connects the collarbone (clavicle) to the shoulder blade (scapula), playing a role in arm movement and stability. Injuries to this joint range from mild sprains to complete tears of the supporting ligaments. Such injuries are particularly prevalent in athletes and can result from various types of trauma.
Understanding the AC Joint
The AC joint is formed by the clavicle and the acromion, a projection from the scapula. It helps connect the upper limb to the rest of the skeleton. While it allows only gliding movement, it contributes to the overall range of motion of the scapula and assists in arm movements like shoulder abduction and flexion.
The stability of the AC joint relies on several ligaments. The acromioclavicular (AC) ligaments directly surround the joint capsule, connecting the acromion and clavicle. The coracoclavicular (CC) ligaments also provide stability. These strong ligaments connect the clavicle to the coracoid process of the scapula, preventing excessive vertical movement and rotation of the joint.
How AC Joint Tears Occur
AC joint tears result from forces pushing the shoulder blade away from the collarbone, stretching or tearing the supporting ligaments. A common mechanism is a direct blow to the tip of the shoulder, which can force the acromion downward beneath the clavicle. This often happens during falls directly onto the shoulder.
Injuries also occur through indirect forces, such as falling onto an outstretched hand or elbow. This transmits an upward force through the arm, impacting the AC joint. Sports injuries, especially in contact sports like Australian football, rugby, or cycling, frequently cause AC joint tears. Accidents like car collisions can also lead to these injuries.
Recognizing an AC Joint Tear
Pain on top of the shoulder is a common indicator, which can sometimes radiate to the neck, chest, or back. This pain may feel sharp when moving the shoulder or a dull ache at rest.
Swelling and bruising may occur around the affected joint. Tenderness to the touch over the AC joint is typical. In more severe cases, a noticeable bump or deformity may appear on the top of the shoulder, indicating that the clavicle has shifted upward due to ligament damage. Limited range of motion in the shoulder, particularly when attempting to lift the arm, is another common sign.
Diagnosis and Treatment Options
Diagnosis begins with a physical examination. The doctor will assess the shoulder for tenderness, swelling, and any visible deformity, and evaluates the range of motion. Specific tests, such as palpating the joint or performing maneuvers that apply pressure to the AC joint, can help pinpoint the source of pain.
Imaging studies confirm the diagnosis and determine injury severity. X-rays are taken to rule out fractures and visualize the alignment of the bones, which helps in grading the tear. An MRI may assess soft tissue damage, such as the extent of ligament tearing. AC joint tears are graded based on the severity of ligament damage, ranging from Grade I (mild sprain with stretched ligaments) to Grade III (complete tear of both acromioclavicular and coracoclavicular ligaments) and higher, with increasing displacement of the clavicle.
Treatment approaches vary depending on the grade of the AC joint tear. Non-surgical management is common for lower-grade tears. This involves rest, ice, and a sling for immobilization. Pain medication may be prescribed.
Once the initial pain subsides, physical therapy is initiated to help restore strength, flexibility, and full range of motion to the shoulder. Rehabilitation aims to regain function and prevent stiffness. For more severe tears, such as Grade III and higher, surgical intervention may be considered to stabilize the joint and reconstruct the torn ligaments. Surgery depends on the degree of joint instability and the patient’s activity level. Treatment aims to alleviate pain, restore stability, and allow the individual to return to their normal activities.