1. Definition: A hammer fracture is an avulsion of the extensor tendon in the hammer finger accompanied by a fracture of the dorsal articular margin of the distal phalanx. It is usually the result of an acute flexion force contusion in the extension position and is commonly seen in the little finger, ring finger and middle finger and may develop into a goose neck deformity and laxity of the extensor apparatus if left untreated. The avulsed bone fragment at the extensor tendon stop is referred to as a hamate fragment. If the hamate fragment is rotated or angulated, it will interfere with anatomic repositioning and may result in nonunion and deformity. It is necessary to reset the rotation and angulation during treatment. Wehbe´ and Schneider classify the fracture according to the lateral radiographs: I: no subluxation of the distal interphalangeal joint; II: with subluxation; III: with damage to the epiphysis and diaphysis. According to the size of the fracture mass: a: less than 1/3 joint surface, b: 1/3-2/3 joint surface, c: more than 2/3 joint surface. Most of the hammer fingers can be treated conservatively, but those with a bone block larger than 1/3 joint surface and difficult-to-recover distal interphalangeal joint dislocation need surgery, that is, 2b and 2c of the above classification. 4.Surgical method Fig. 1: percutaneous (no incision) dorsal block nail surgical fixation, the disadvantage is that there are still some rotations can not be corrected Fig. 2, 3, modified surgical method: 22G needle as a joystick to rotate and reset the hammer-shaped bone block. 5, postoperative treatment The pin was removed at 6 weeks, and normal activities were performed after 1 week of passive exercise.