Irreducible dorsoulnar dislocation of the proximal phalanx of the thumb

A case of irreducible complete dorsoulnar dislocation of the proximal phalanx of the thumb is presented. The pathologic anatomy included intersubstance tears of the ulnar collateral ligament and dorsal capsule and avulsions of the palmar plate and radial collateral ligament from their metacarpal attachments. The palmar plate blocked reduction, as did the radial collateral ligament that was caught on the margin of a tear in the adductor aponeurosis and on the tendon of the extensor pollicis longus. A review of the English-language literature indicates that this pathologic anatomy has not been described.