The second and third metacarpals are relatively immobile, and fractures require anatomic reduction. The fourth and fifth metacarpals have 15 to 20° AP motion, which allows for some compensation. Metacarpal fractures are categorized as head, neck, shaft, or base fractures.
HEAD Fractures of the metacarpal head are usually due to a direct blow, crush, or missile. These fractures are distal to the insertion of the collateral ligaments and are often comminuted. If a laceration is present, a human bite must be considered. Treatment consists of ice, elevation, and immobilization with referral to a hand surgeon.
NECK Fractures of the metacarpal neck are usually due to a direct impaction force. A fracture of the fifth metacarpal neck is often referred to as a boxer's fracture. These fractures are usually unstable with volar angulation. Angulation of less than 20° in the fourth and 40° in the fifth metacarpal will not result in functional impairment. If greater angulation in these metacarpals occur, reduction should be attempted. In the second and third metacarpal, angulation of <15° is acceptable. These fractures should be splinted with the wrist in 20° extension and the MP flexed at 90°. Fractures of the second or third metacarpal that are significantly displaced or angulated require anatomic reduction and surgical fixation.
SHAFT A direct blow usually injures fractures in this region. Rotational deformity and shortening are more likely in shaft fractures than in neck fractures. If manipulative reduction is necessary, operative fixation is usually indicated.
BASE Fractures at the base of the metacarpal are usually due to a direct blow or axial force. They are often associated with carpal bone fractures. Fractures at the base of the fourth and fifth metacarpal can result in paralysis of the motor branch of the ulnar nerve.
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