Define Acromioclavicular Joint Injuries. Describe its clinical features, classification and treatment.

Mechanism and Clinical Features

Injuries of the acromioclavicular (AC) joint usually follow a fall directly onto the point of the shoulder with the arm adducted. There is tenderness and swelling over the AC joint, and in higher grades a visible 'step' deformity as the outer end of the clavicle rides upward. The 'piano-key' sign — the clavicle springs back up when pressed down — indicates disruption. Stability depends on two ligament groups: the acromioclavicular ligaments (horizontal stability) and the coracoclavicular ligaments (vertical stability).

Classification and Management (rockwood)

The Rockwood classification grades the injury by which ligaments are torn and the degree of displacement, and this determines treatment.

Imaging

An AP view of both shoulders allows comparison of the coracoclavicular distance and the joint alignment with the normal side; an increase indicates a torn coracoclavicular ligament (type III or above). Weighted ('stress') views, once used to unmask subtle subluxation, are now rarely needed. Higher-grade or posteriorly displaced (type IV) injuries may need an axillary view or CT to define the displacement.

Principle of Treatment

• Low-grade injuries (I–II) are treated conservatively with a sling and early mobilisation, and the great majority do well.
• Type III is controversial and most are managed non-operatively — a residual bump may persist but function is usually good — with surgery reserved for young, athletic or heavy-manual patients.
• The severe types (IV–VI) require operative reduction and reconstruction of the coracoclavicular ligaments.

Grades I–II conservative; higher grades may need fixation.

• AC joint injury follows a fall onto the point of the shoulder; features are AC tenderness, a 'step' deformity and a positive 'piano-key' sign.
• Stability = AC ligaments (horizontal) + coracoclavicular ligaments (vertical).
• Rockwood I–II (CC ligaments intact) → conservative. Type III (both torn) → usually conservative, surgery for high-demand patients.
• Rockwood IV–VI (severe displacement) → operative reconstruction.