Acromioclavicular Joint Injury

Overview

This StatPearls review by Kiel, Taqi and Kaiser, last updated in September 2022, covers injuries of the acromioclavicular (AC) joint. They make up more than 40% of shoulder injuries and nearly 10% of all injuries in collision sports such as football, lacrosse and ice hockey, and often follow sport, falls from a bicycle or car accidents. Mild injuries cause little morbidity, but severe ones can cost the shoulder much of its strength and function, and may come with a clavicle fracture, impingement or, rarely, neurovascular injury.

Anatomy and presentation

The joint is stabilised mainly by the AC ligament, of which the superior part is the most important, and by the coracoclavicular ligaments (trapezoid and conoid), which give vertical stability. The usual mechanism is a direct blow to the lateral shoulder with the arm adducted, or a fall on the outstretched hand or elbow. Patients have anterosuperior shoulder pain, swelling, bruising or a visible deformity, and sometimes a 'piano key' sign, in which the elevated clavicle springs back when pressed down. The whole clavicle, the sternoclavicular joint and the neurovascular status should be checked.

Evaluation and classification

Standard radiographs are usually enough. A Zanca view (beam tilted 10 to 15 degrees cranially), bilateral AP views and weighted stress views help when the diagnosis is uncertain, and ultrasound or MRI are options if doubt remains. The coracoclavicular distance is compared with the other side. The Rockwood classification (types I to VI) guides treatment: type I is an AC ligament sprain, type II tears the AC ligament and sprains the coracoclavicular ligament, type III tears both with a 25 to 100% greater coracoclavicular distance, type IV displaces the clavicle posteriorly, type V is displaced by more than 100%, and type VI is a rare inferior displacement.

Treatment

Types I and II, and many type III injuries, are treated non-operatively with a sling, analgesia, ice and physiotherapy. Surgery is considered for type III injuries with more than 75% displacement, in labourers and elite athletes, when cosmesis matters or when conservative care fails, and types IV to VI usually need surgery. Acute fixation options include the hook plate (which must be removed later), the Bosworth coracoclavicular screw and tension band wiring (both removed at about 8 weeks) and endobutton reconstruction. Chronic injuries are treated with joint debridement, ligament reconstruction and stable fixation, for example by the modified Weaver-Dunn, Mazzocca or docking techniques, and the Mumford procedure is used for painful chronic type I and II injuries.

Prognosis

Most patients treated without surgery regain function by 6 weeks and return to normal activity by 12 weeks. After surgery the arm is immobilised for 6 weeks and full activity returns at about 6 months. Residual pain affects 30 to 50% of patients, and complications include arthritis, hardware irritation, infection and adhesive capsulitis.