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[Skier's thumb--osseous injury and rupture of the ulnar collateral ligament].

Injuries to the ulnar collateral ligament of the thumb are common in down hill-skiing, and are thus called "skier's thumb". In complete disruption of the ligament, surgical treatment is mandatory to restore stability. The management gets more difficult if a bony lesion is present: does a non-displaced fragment represent a non-displaced bony avulsion of the ulnar collateral ligament, thus allowing conservative treatment? We reviewed sixty-three consecutive patients with an acute skier's thumb injury in order to determine the anatomical nature of injuries in thumbs that were treated surgically either for fracture or for instability. Of all 63 thumbs, twenty-five (40%) had a fracture. Surgical exploration showed two types of fractures: a fragment attached to the ulnar collateral ligament, and a fragment not attached to the ulnar collateral ligament. The first type, corresponding to a true avulsion fracture of the ulnar collateral ligament, was found in eight cases. The same fracture type was seen in other seven cases with an additional isolated fragment not attached to the ligament. Such an isolated fragment was observed in ten other cases where the ulnar collateral ligament was completely disrupted. This type of bone fragmentation cannot be differentiated from a bony avulsion of the ulnar collateral ligament on routine films. Therefore, it is mandatory to stress test the injured thumb even when a bony avulsion fracture with no or minimal displacement is suspected on X-ray. The fracture may not represent a bony avulsion, but a fragmentation of the ulnar volar aspect of the proximal phalanx associated with a complete disruption of the ulnar collateral ligament.