An acromioclavicular (AC) tear, often called a shoulder separation, is a common injury resulting from trauma to the shoulder. The AC joint is located at the top of the shoulder, where the collarbone (clavicle) meets the acromion (part of the shoulder blade). An AC tear involves damage to the supporting ligaments of this joint, leading to instability or displacement of the clavicle relative to the acromion.
Understanding the AC Joint and How Tears Happen
The stability of the AC joint is maintained by two primary sets of ligaments: the acromioclavicular (AC) ligaments, which run horizontally, and the coracoclavicular (CC) ligaments, which run vertically between the clavicle and the coracoid process. The AC ligaments primarily resist horizontal movement, while the stronger CC ligaments provide the majority of the vertical stability. Disruption of these ligaments defines the severity of an AC tear.
The most frequent mechanism of injury is a direct blow to the point of the shoulder, typically from falling directly onto the shoulder tip during sports or an accident. This force drives the acromion downward while the clavicle is held in place, creating shear stress on the ligaments. The sequential tearing of the ligaments—first the AC, then the CC—is directly related to the magnitude of the force applied. When the ligaments tear, supporting muscles like the deltoid and trapezius may also be damaged, contributing to clavicle displacement.
The Grading System for AC Tears
AC tears are classified into six grades based on the degree of ligament damage and resulting clavicle displacement, which guides treatment decisions. Grade I is the mildest injury, involving only a sprain or stretching of the AC ligaments without significant tearing or joint displacement. The CC ligaments remain intact, and the joint appears normal on X-ray.
A Grade II tear involves a complete rupture of the AC ligaments, though the CC ligaments are only sprained or partially torn. This results in a slight widening of the AC joint and minor upward displacement of the clavicle, which may create a small, visible bump. Grade III signifies a severe tear where both the AC and CC ligaments are completely ruptured. This failure allows for marked upward displacement of the clavicle, with the distance between the clavicle and coracoid process increasing by 25% to 100% compared to the uninjured shoulder.
Grades IV, V, and VI represent increasingly severe and complex injuries that are less common. Grade IV involves the clavicle being displaced backward into the trapezius muscle, a posterior displacement often difficult to see on standard X-rays. Grade V is a more severe version of Grade III, featuring extreme superior displacement (often more than 100% elevation) due to the complete detachment of the deltoid and trapezius muscle fascia. Grade VI is extremely rare and involves the clavicle being displaced downward, lodging under the coracoid process.
Diagnosis and Initial Management
Diagnosis typically begins with a thorough physical examination and a patient history detailing the mechanism of injury. A physician checks for localized tenderness and swelling directly over the AC joint. For higher-grade injuries, a visible deformity or “step-off” sign, where the clavicle appears prominent above the acromion, may be observable.
Imaging studies are necessary to confirm the diagnosis and accurately classify the grade of the tear. Standard X-rays, often including an angled Zanca view, are used to visualize the joint space and the vertical relationship between the clavicle and the acromion. In some cases, a “stress view” X-ray (where the patient holds a weight) may be performed to better assess clavicle displacement, though the routine use of this technique is debated.
Initial management focuses on pain control and preventing further injury. Immediate care includes rest of the injured arm, application of ice to reduce swelling, and temporary immobilization in a sling. Over-the-counter or prescription pain and anti-inflammatory medications are used to manage discomfort in the acute phase. The goal is to settle acute symptoms before determining the definitive treatment pathway.
Treatment Pathways and Recovery
Treatment for AC tears is directly correlated with the injury grade and resulting joint stability. Conservative, non-surgical management is the standard of care for the majority of Grade I and Grade II injuries. This approach involves rest and immobilization in a sling for comfort, often lasting one to three weeks. Once acute pain subsides, a structured physical therapy program begins to restore full range of motion and strength. Most individuals with Grade I and II tears can expect a return to full activity within two to six weeks.
The management of Grade III tears is considered controversial and depends on the patient’s age, activity level, and profession. For most adult patients, non-operative care (sling, pain management, and physical therapy) leads to an excellent functional outcome, despite the persistent “bump” or deformity. Surgical intervention may be considered for young, highly active patients, those who engage in heavy labor, or those with persistent pain or functional deficits after three months of conservative care.
Grades IV, V, and VI injuries almost always require surgical intervention due to extreme instability and clavicle displacement. Surgery aims to reconstruct the torn CC ligaments and reduce the clavicle back into its correct anatomical position, often using strong sutures or synthetic grafts for stabilization. Recovery following surgery is significantly longer than conservative treatment, typically requiring immobilization for four to six weeks, followed by lengthy rehabilitation. The goal of any treatment is to restore full, pain-free range of motion and strength.