Perilunate and lunate dislocation

Mayfield I–IV

Lesser and greater arc carpal injuries

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High-energy wrist injuries that tear the ligaments around the lunate in sequence. Up to a quarter are missed at first. On the lateral view the radius, lunate and capitate should stack in a straight line ("three cups").

Transscaphoid perilunate fracture-dislocation, PA and lateral. On the PA view the scaphoid is fractured and the carpal rows overlap; on the lateral the lunate stays on the radius while the capitate is displaced dorsally. — Hellerhoff, CC BY-SA 3.0, via Wikimedia Commons.

Mechanism

Fall from height or motorbike crash with the wrist extended, ulnarly deviated and supinated.

Clinical findings

Painful, swollen wrist that looks less deformed than the injury deserves.
Median nerve compression (acute carpal tunnel syndrome) is common: check sensation and treat urgently.

Imaging

PA: broken Gilula arcs, the lunate looks triangular ("piece of pie"). Lateral: the capitate is out of the lunate cup (perilunate) or the lunate is tipped volarly ("spilled teacup"). CT for associated fractures.

Classification

Mayfield I: Scapholunate ligament tear.
Mayfield II: + capitolunate disruption.
Mayfield III: + lunotriquetral tear: perilunate dislocation.
Mayfield IV: Lunate dislocation.
Lesser vs greater arc: Lesser arc: ligaments only. Greater arc: through bones (trans-scaphoid, transradial styloid, transcapitate, transtriquetral).

Types shown in 3D

Perilunate (dorsal): Lesser-arc injury: the lunate stays on the radius and the rest of the carpus dislocates dorsally around it. The capitate no longer sits in the lunate cup on the lateral view.
Lunate dislocation: The end stage (Mayfield IV): the capitate drops back into line with the radius and pushes the lunate out volarly; the lunate tips over like a "spilled teacup". It can compress the median nerve in the carpal tunnel.
Trans-scaphoid perilunate: Greater-arc injury: the force passes through the scaphoid. The proximal pole stays with the lunate, the distal scaphoid goes with the carpus. The commonest pattern of greater-arc injury.

Treatment

Emergency: Prompt closed reduction under anaesthesia and splint; urgent carpal tunnel release if median nerve symptoms persist.
Definitive: Open reduction and repair of the scapholunate and lunotriquetral ligaments with K-wire or screw fixation of the carpus (dorsal ± volar approach); fixation of the scaphoid in trans-scaphoid injuries.

Aftercare

Cast 8–12 weeks, K-wires removed at about 8 weeks, then therapy.

Complications

Missed injury (chronic dislocation: salvage only)
Median nerve injury
Carpal instability and post-traumatic arthritis
Avascular necrosis of the lunate or scaphoid