AC Joint Separation

Acromioclavicular (AC) Joint Separation

An acromioclavicular (AC) joint separation is an injury that occurs at the joint connecting the clavicle (collar bone) and the acromion (a part of the shoulder blade, or scapula). It commonly happens with a direct blow to or a fall onto the shoulder. For example, a cyclist falling over the handlebars onto their shoulder or a football player being struck by another player.

Anatomy and Pathophysiology

The articulation between the acromion of the scapula and the lateral clavicle make up the AC joint. In between the bones, a fibrocartilaginous intra-articular disc is found, analogous the meniscus of the knee joint. AC ligaments course between the two bony ends, controlling horizontal motion and anterior-posterior stability. Stability at the AC joint is also reinforced by the coracoclavicular (CC) ligaments, which control vertical and superior-inferior stability. 

Symptoms

Pain occurs on the top of the shoulder, and often worsens with lifting or cross body reaching. A bump or deformity is noted at the AC joint, and localized bruising may be present. 

Physical Examination and Work-up

On physical examination, the thigh is examined for tenderness and/or ecchymosis/bruising. Additionally, strength and neurovascular testing are conducted. In some, the sciatic nerve may be involved in hamstrings injury.

Imaging

X-rays are assessed for position of the clavicle relate to the acromion and for the presence of a concomitant fracture. 

Classification

Type IAC ligament sprain
Type IIAC ligament disrupted; increased CC distance < 25% of contralateral
Type IIIAC and CC ligament disrupted; increased CC distance 25-100% of contralateral
Type IVAC and CC ligament disrupted; lateral clavicle displaced posteriorly through the trapezius
Type VAC and CC ligament disrupted; increased CC distance > 100% of contralateral
Type VIAC and CC ligament disrupted; rare inferior dislocation of the lateral clavicle

Management of AC Joint Injuries

The goal of treatment, both non-surgical and surgical, is to restore function and reduce pain. The majority of AC joint injuries are managed without surgery, including rest, activity modification, physical therapy, Kinesiotaping, ice and over the counter anti-inflammatories. 

Surgery is indicated in the setting of more severe injuries and involves restoration of the CC interval with ligament reconstruction. Following surgery, the repair is protected sling immobilization for 6 weeks. A specific rehab protocol is issued based on intra-operative findings and guided by desired activities and patient goals.