Acromioclavicular dislocation

Rockwood I–VI

AC and coracoclavicular ligaments

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A fall onto the point of the shoulder drives the acromion down while the clavicle stays: the acromioclavicular ligaments tear first, then the coracoclavicular ligaments (conoid and trapezoid). The more ligaments torn, the higher the lateral clavicle stands.

AC joint dislocation (Tossy III / Rockwood III), stress view. With a 10 kg weight the right lateral clavicle rides well above the acromion compared with the normal left side. — Hellerhoff, CC BY-SA 3.0, via Wikimedia Commons.

Mechanism

Direct fall onto the tip of the shoulder with the arm adducted (cycling, contact sports).

Clinical findings

Step at the AC joint, tenderness; piano-key sign (the clavicle can be pushed down and springs back).
Type IV: posterior displacement felt from above; check the skin over the clavicle in type V.

Imaging

Zanca view (AP tilted 10–15° up) and axillary view; compare with the other side and measure the coracoclavicular distance.

Classification

I: AC sprain, no displacement.
II: AC torn, CC intact; less than 25% displacement.
III: AC and CC torn; 25–100%.
IV: Clavicle displaced posteriorly into the trapezius.
V: 100–300% upward displacement, deltotrapezial fascia stripped.
VI: Clavicle below the coracoid.

Types shown in 3D

Rockwood I: Sprain of the acromioclavicular ligaments; the joint is not displaced.
Rockwood II: AC ligaments torn, coracoclavicular (CC) ligaments intact: the clavicle rides up by less than its own thickness.
Rockwood III: AC and CC ligaments torn: the lateral clavicle stands up by 25–100% (in reality the shoulder droops under the weight of the arm). Most are treated without surgery.
Rockwood IV: The lateral clavicle is driven backwards through or into the trapezius. Seen on the axillary view. Operative.
Rockwood V: Gross upward displacement (100–300%): the deltotrapezial fascia is stripped off the clavicle. Operative: hook plate, or coracoclavicular reconstruction.

Treatment

Types I–II: Sling for comfort, early movement; return to sport in 2–6 weeks.
Type III: Non-operative for most; surgery for heavy labourers, overhead athletes or persistent pain and scapular dyskinesia.
Types IV–VI: Reduction and stabilisation: hook plate, coracoclavicular suture-button fixation, or ligament reconstruction (anatomical CC reconstruction) for chronic cases.

Aftercare

Hook plates are removed after about 3 months.

Complications

Persistent deformity (usually cosmetic)
AC joint arthritis
Loss of reduction after fixation
Coracoid or clavicle fracture after tunnel fixation