Metacarpal fractures, result from trauma to the bones located in the palms (Metacarpal bones). These bones are made up of a head, neck, body, and base. The most commonly affected bone is the fifth metatarsal, known as street fighter's boxer fracture, which is connected to the fifth digit (small finger). Possible causes of fifth metacarpal fracture include punching with a clenched fist (most common cause), blunt force trauma, or crush injuries. Increase incidence is observed in males compared to females. If the cause of injury is a direct blow to a clenched fist, the most commonly affected location is the neck of the metatarsal bone, but may happen at any other part of the bone. Once fractured, angulation might be noted, this results in part to the forces exerted at the metatarsal bones by the interosseous muscles.
Signs and symptoms of a fifth metatarsal fracture include pain with increased intensity at the site of injury, bruising, swelling, shortened fingers, and deformities loss of knuckle contour. On physical examination it is important to carefully inspect the skin for any break; perform a detailed neurovascular examination to assess sensation, motor function, and blood flow; and assessment of rotational alignment which is very important in determining management. The latter can be tested by examining the hand with the metacarpophalangeal (MCP) joint and proximal interphalangeal (PIP) joint flexed and the distal interphalangeal (DIP) joints extended. Malrotation would be suspected if the fifth finger does not converge with the others when drawing lines along with the digits.
Imaging studies (X-rays) are required to confirm the diagnosis, along with history and physical examination. X-rays in the anteroposterior, lateral and oblique views are usually ordered to assess the severity of the injury. A lateral view is required to determine the degree of angulation. Normally angulation of the metacarpal head to the neck is approximately 15 degrees.
Treatment will depend on the degree of angulation, opened versus closed wound, and if there is malrotation. If the injury is closed, and there are no signs of angulation, malrotation, or displacement; immobilization with a splint can be considered. When splinting it is important to have slight wrist extension, MCP joint flexed approximately 70 – 90 degrees, the PIP and DIP mildly flexed. This positioning protects the range of movement and normal function due to a decrease in the risk of ligament shortening. If the injury resulted in more than 30 degrees of angulation, closed reduction may be required. During this procedure the MCP, PIP, and DIP joints are in a flexed position of approximately 90 degrees; pressure is applied to the dorsal side of the fracture while also being exerted axially on the PIP joint. The hand is immobilized once the reduction of the fracture is completed. If there are open fractures, neurovascular damage, or malrotation surgical management is the preferred method of treatment. The different types of surgeries are closed reduction with percutaneous pinning or open reduction with internal fixation.
After the treatment, it is important to monitor the injury after one week with repeat x-rays to assess correct alignment. It usually will take approximately four to six weeks to observe signs of healing and thus, x-rays should continue to be obtained every two weeks. It is important to note that some cosmetic changes may persist.