Clinical Example: Perilunate Instability

The lunate, like other carpal bones , has no muscular attachments, and its position relative to its neighbors depends on adjacent compressive forces and ligamentous restraints. Perilunate instability results from insufficiency of its restraining ligaments. The lunate posture fails into dorsal rotation and palmar subluxation more often than into the opposite orientation. This may result in either subluxation or lunate dislocation. Acute trauma may result in either purely ligamentous perilunate instability or perilunate fracture-dislocations.

This patient presents with  a history of morning wrist stiffness and pain, not limiting activities. He plays golf daily. He has a full painless range of wrist motion, although intermittently develops a firm mid dorsal prominence which can be corrected with local pressure. There is no history of major trauma, but the patient has sustained many falls over his life from imbalance due to  Friedreich's ataxia. Xrays show scapholunate dissociation with dorsal scaphoid rotation:

Minimal passive manipulation results in dorsal lunate dislocation which can be reduced easily, all without pain:

Fluoroscopy confirms painless dorsal lunate dislocation, reduced with finger pressure on the dorsal lunate. This presents a treatment dilemma, as he has full range of motion, and despite intermittent pain, no limitations of daily activity.

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