In Depth: Muscles
The hand has several muscles. Some make broad, smooth movements, and others make small, finite movements. It’s the combination of the exterior and deep muscles of the hand and forearm that allow the hand to perform such detailed tasks.
Some of the muscles, tendons, and ligaments of the hand, as well as those of the forearm that affect hand movement, include:
- Extensor digitorum: This forearm muscle is responsible for extending all of the fingers of the hand except the thumb.
- Palmaris longus: This is a slender triangle-shaped tendon, a fibrous band that connects muscles to bones, on the palm. Interestingly, about 14 percent of the population does not have this tendon, but its absence has not shown any difference in hand function.
- Flexor retinaculum: This strong band of fibrous ligament, material that connects bone to bone, stretches across the back of the wrist. It affects muscles that help flex the hand.
- Extensor retinaculum: Close to the flexor retinaculum, this ligament affects muscles that help extend fingers and other parts of the hand.
- Abductor pollicis longus: This forearm muscle helps pull the wrist and the thumb away from the body. It is important in holding small objects such as a pencil.
- Extensor pollicis brevis: Another important forearm muscle, this one acts in conjunction with the abductor pollicis longus to extend and abduct the thumb.
- Flexor digitorum profundis: This long forearm muscle flexes the wrist and fingers.
- Pronator teres: This muscle begins at the top of the humerus, crosses the forearm, and connects to the ulna. It helps turn the palm downward.
Carpal tunnel syndrome is a condition caused by repeated movements, such as regular use of a computer keyboard or mouse. Characterized by tingling and numbness in the hands or fingers, this syndrome causes pressure on the median nerve, the one that runs through the wrist on the thumb side of the hand. Special devices, such as braces or specialized keyboards, or technique changes can improve the condition, but sometime surgery is needed to relieve the pressure.
In carpal tunnel surgery, a surgeon cuts the palmar carpal ligament, a band of fibrous material that stretches across the wrist like a watchband. This cut relieves pressure on the median nerve without severely damaging the hand.