How are AC joint injuries classified?
AC joint injuries are rated by the severity of injury to the AC joint capsule and surrounding ligaments and graded into six different classifications.
Grade 1: Minimal to no AC joint displacement. The AC joint capsule might be stretched or partially torn. There is no obvious shoulder deformity as the AC joint capsule and CC ligaments remain intact. This is the most common type of AC joint injury.
Grade 2: Minimal to moderate AC joint displacement. The AC ligament is completely torn. The CC ligaments may remain intact or encounter a partial tear. This type of injury can predispose the AC joint to arthritis due to misalignment of the joint.
Grade 3: Complete separation of the AC joint. There is often an obvious shoulder deformity with this injury as the ligaments and cartilage of the AC joint in addition to the CC ligaments are completely torn.
Grades 4-6: The most severe types of AC joint injuries that involve the complete disruption of the AC joint capsule in addition to the CC ligaments. This occurs from a high-impact force directly on the shoulder seen with motor vehicle collisions. Other more severe muscle injuries occur with these high grade conditions. These instances are rare and require surgical reconstruction.