Acromioclavicular Joint Injuries: From Sprains to Complete Separations

The Acromioclavicular Joint

The acromioclavicular (AC) joint is the articulation between the lateral clavicle and the acromion — the bony projection of the scapula that forms the roof of the shoulder. It is stabilised by two sets of ligaments: the acromioclavicular ligaments (superior and inferior AC ligaments), which resist horizontal translation of the clavicle; and the more important coracoclavicular ligaments (conoid and trapezoid), which suspend the scapula and arm from the clavicle and resist vertical separation. The AC joint transmits loads between the upper limb and the axial skeleton during pushing, pulling, and overhead activities, and must accommodate the clavicle's rotation during full arm elevation.

Mechanism of Injury

AC joint injuries most commonly occur from a direct fall onto the point of the shoulder — the acromion is driven inferiorly relative to the clavicle, progressively stressing and tearing the AC and then coracoclavicular ligaments. This mechanism is common in contact sports (AFL, rugby, cycling), falls from height, and motor vehicle accidents. The Rockwood classification grades AC joint injuries from I (AC ligament sprain, no displacement) through VI (rare, severe inferior clavicle displacement), with grades I–II being sprains, grade III being complete AC and CC ligament disruption with moderate displacement, and grades IV–VI representing severe displacement requiring surgical consideration.

Management by Grade

Grades I and II are managed conservatively: initial rest, ice, and a sling for comfort (not prolonged immobilisation), followed by early mobilisation, rotator cuff and periscapular strengthening, and return to sport over two to six weeks. Grade III injuries are the most contested in the literature — the majority of patients achieve excellent outcomes with conservative management including structured rehabilitation, and operative intervention does not consistently outperform conservative treatment in return-to-sport or functional outcomes at medium-term follow-up. Surgical consideration is appropriate for grade III injuries in high-demand overhead athletes or those with persistent symptoms beyond three months. Grades IV–VI generally require surgical stabilisation to reduce the displacement and restore coracoclavicular integrity. Post-operative rehabilitation progressively restores range of motion, rotator cuff and scapular muscle strength, and functional integration.

Rehabilitation Principles

Regardless of grade, rehabilitation targets the same deficits: periscapular muscle strength (particularly lower trapezius and serratus anterior, which maintain scapular position on the thorax), rotator cuff activation for dynamic glenohumeral stabilisation, and progressive loading into horizontal push and pull patterns. Manual therapy to the AC joint, cervical spine, and thoracic spine reduces pain and restores mobility. Return to contact sport requires full pain-free range, strength symmetry, and sport-specific movement capacity — not simply the passage of time.