Scapholunate dissociation

The scapholunate dissociation (stage I perilunate injury) is a purely ligamentous injury and part of a lesser arc injury. The scapholunate ligament is partially or completely torn.

• Perilunate injury classification

It is usually caused by a fall on the pronated hand (palm down) in dorsiflexion at the wrist.

The diagnosis is made by clinical and radiological assessments. If uncertainties remain, arthroscopic assessment may be helpful.

‘Arcs’ are lines that can be drawn or imagined on x-ray/CT images of the hand and wrist to help assess the alignment of the carpal bones. A discontinuity in an arc indicates a malalignment of the carpal bones either by the fracture or dislocation and should lead to further investigation, eg, CT scan.

Variations of injury patterns can be identified depending on which carpal bones and ligaments are affected and the direction of any dislocation or fracture displacement.

Greater arc injuries comprise fracture-dislocations of the scaphoid, capitate, hamate, and/or triquetrum.

Lesser arc injuries are pure ligamentous injuries around the lunate.

The concept of ‘arcs’ helps to identify the location and extent of a complex carpal injury.