July 15, 2006
Anatomy of the Hand & Wrist
by Anne Kossacheff, YKHC Physical Therapist
Humans rely on the intricate structure of the hands to survive. We use our hands to eat and work and also to express our thoughts through gestures and sign language.
There are three groups of bones in the wrist and hand: eight carpal bones (in the wrist itself), five metacarpal bones (in the palm area of your hand) and 14 phalanges (the long bones in your fingers and thumb).
These bony structures are joined to each other via different types of joints. There are also long and short muscles in your hand, inserting onto the bones to provide unique movement of the fingers and hand. Finally, hands are covered by skin that is different from the skin covering other parts of the body. The hand has rich vascular and neural structures to manage its unique functions.
Wrist anatomy
There are eight carpal bones made up of two rows of four bones each. The carpal bones connect to the ulna and radius (remember these bones from before?). If you hold the end of your forearm, just past the bone that sticks out of the side of your wrist, you are holding your carpal bones. The carpal tunnel is on the palm side of your wrist in this area. It is about the diameter of your thumb. There are 3 tendons, and 1 nerve that run through this tunnel and into your hand. Any irritation or inflammation in this tunnel can put pressure on the nerve, causing numbness, tingling, and/or weakness in the hand. As you can see in the picture (*figure 1), the median nerve going through the tunnel innervates a different area of the hand than the ulnar nerve outside the tunnel. Symptoms in the area innervated by the median nerve are called "carpal tunnel syndrome," and can be very serious. It is best to address this problem when you first notice symptoms, as
permanent nerve damage can occur if the pressure remains on the nerve for an extended period. Also in figure 1, you can see the transverse carpal ligament. This is the "roof" of the carpal tunnel, and only a small portion of the ligamentous system that holds the wrist and hand together. Any fall or trauma to the wrist and hand can damage the ligaments, potentially resulting in painful movement long after the injury, especially if the ligaments are stressed too soon after an injury.
Hand and Finger Anatomy
Each hand has five metacarpal bones. There are small muscles running between the metacarpal bones called lumbricales and interossei. There are a total of 14 phalanges in each hand. Each finger contains three phalanges, but each thumb only has two.
The muscular structures in the fingers are complicated and intricate. Each finger has two muscles to provide a flexion motion, two to provide an extension motion, as well as getting assistance for these motions from the interossei and lumbrical muscles. Each joint in the fingers and throughout the hand has its own cartilage, joint capsule and ligaments holding the bones together. When you "jam" your finger or thumb, you have sprained your ligaments, and perhaps done damage to the cartilage in the joint. This often takes some time to heal, as it is nearly impossible to allow the hand to fully recover before using it. Their initials often name the knuckles and joints of the wrist and hand. Where do you think the metacarpo-phalageal joint is located? Look at figure 2. Find the metacarpals, and then find the phalanges. The joint between these bones is the metacarpo-phalageal joint, or MCP. Where do you think the CMC and IP joints are? (See answers at the end of the column).
Next month we will have more information about the intricacies of the fingers, and give you some ideas on how to prevent injury to the wrist, and rehabilitate an injury you may have already had to the hand or wrist.
Answers: The CMC is the carpo-metacarpal joint - between the wrist and the hand itself. The IP joints are inter-phalangeal joints - each finger had two, and the thumb has one. The IP joins are the knuckles in your fingers.