Perilunate Dislocation

Perilunate dislocations and fracture-dislocations are high-energy carpal injuries in which the lunate loses its normal articulation with the surrounding carpal bones — the capitate, scaphoid, triquetrum, and hamate are displaced dorsally while the lunate remains (at least initially) in the lunate fossa of the distal radius. They result from a fall onto an outstretched hand in hyperextension, ulnar deviation, and intercarpal supination, and are classified by the Mayfield progressive perilunar instability sequence (Stages I–IV) and by whether the injury follows the lesser arc (purely ligamentous) or the greater arc (through bone, most commonly as a trans-scaphoid perilunate fracture-dislocation). Diagnosis is frequently delayed or missed — up to 25% are not identified at initial presentation — because the wrist radiograph appearances can appear deceptively normal to the untrained eye, and the key diagnostic sign is loss of the three smooth carpal arcs (Gilula's lines) on the AP view combined with the triangular pie-slice shape of the lunate on the lateral view. Median nerve compression within the carpal tunnel is the most common associated neurological injury, presenting as acute carpal tunnel syndrome with thenar paraesthesia and weakness. Treatment is almost always surgical — emergent closed reduction (under sedation or general anaesthesia) is performed acutely to decompress the median nerve and restore carpal alignment, followed by definitive open reduction, intercarpal ligament repair, and Kirschner wire stabilisation within 5–7 days. The surgical approach requires both a dorsal approach (to reduce and pin the carpus and repair the dorsal ligaments) and a volar approach (to decompress the carpal tunnel and repair the scapholunate and lunotriquetral ligaments from the volar side). Despite anatomical reduction and meticulous ligament repair, long-term outcomes are frequently complicated by persistent carpal instability, post-traumatic wrist arthritis, and reduced grip strength, with outcomes deteriorating significantly with delayed diagnosis beyond three weeks.