The main structure of the human hand is made up of a collection of bones called the metacarpals. There are five of these cylindrical bones which connect the phalanges, or finger bones, to the carpus bones in the wrist. Known collectively as the metacarpus, they form the framework for the back and palm of the hand.
Each of the five metacarpals leads to a single finger bone. They are referred to by numbers one through five, with number one being the bone which connects to the thumb and number five being the one that connects to the pinky finger. The points of connection with the fingers are called the knuckles. The bones are covered by skin on the back of the hand, as well as connective tissue on the palm.
The shape and structure of the four metacarpals connecting to the fingers are fairly similar, with a relatively narrow shaft and wider base and head, though their lengths vary. The first metacarpal, which connects to the thumb, is shorter and thicker than the others, with a slightly different shape to the base and head. This helps allow for the opposable movement of the thumb, which enables people to grasp objects with their hands.
Injuries to the back or palm of the hand may involve a fracture of one or more of the metacarpals. This type of break typically occurs due to a fall where the person lands on his or her hand, an injury during sports where there is a significant amount of impact to the hands, or during a fistfight. Often, bruising, swelling, and pain will be present around the location to indicate the presence of a fracture. The majority of metacarpal fractures can be treated by immobilizing the hand using a cast for about six weeks. Some minor physical therapy to help increase range of motion may be necessary afterward, as the hand can become stiff as it heals.
In some cases, damage to the metacarpals may be severe enough to require surgical correction. More than one fracture or a broken bone that penetrates the skin may be too severe for a cast to correct. A bad break may cause a finger to get shorter, and an operation may be needed to restore its former length. Fingers can also become rotated due to metacarpal breaks, and surgery will be needed to put them back in place.