Lateral depression of metacarpal bone. The position of Kirschner wire in cat metacarpal fracture is located in the lateral depression of metacarpal bone, and the movement of metacarpophalangeal joint is not affected when the needle is inserted. Kirschner wire is a commonly used internal fixation material in orthopedics. Its original specification is about 20 cm, and its diameter is between 0.5 and 2 mm. There are several different specifications.