Wrist

The human wrist is a complex anatomical region. It serves as the critical connection between the forearm and the hand. Scientists define the wrist in several different ways. One definition focuses on the carpus, which is a group of eight small bones. Another definition refers specifically to the radiocarpal joint. This is the joint where the radius bone meets the carpal bones. A third definition views the wrist as the entire anatomical region. This region includes the forearm bones and the metacarpal bones of the hand.

To understand how the wrist works, we must look at its specific joints. The radiocarpal joint is an ellipsoid joint. This means it is shaped like an oval or an egg. It connects the radius to the first row of carpal bones. The first row includes the scaphoid, lunate, and triquetrum bones. The distal radioulnar joint, or DRUJ, is also vital. This is a pivot joint located between the radius and the ulna. It is formed by the head of the ulna and the ulnar notch of the radius. The DRUJ works with the elbow to allow for pronation and supination. These are the movements used to turn your palm up or down.

The wrist contains a total of 13 bones in the hand proper. This group consists of eight carpal bones and five metacarpal bones. The carpal bones are organized into two distinct rows. The proximal row includes the scaphoid, lunate, triquetrum, and pisiform. The distal row includes the trapezium, trapezoid, capitate, and hamate. These rows are separated by the midcarpal joint. This joint has a unique S-shape. The bones within each row are connected by intercarpal joints. These joints are strengthened by various ligaments, such as the radiocarpate and interosseous ligaments.

Movement in the wrist is driven by extrinsic hand muscles. These muscles are actually located in the forearm. When these muscles contract, they pull on long tendons. To prevent these tendons from lifting like bowstrings, the body uses retinacula. The flexor retinaculum sits on the palmar side. The extensor retinaculum sits on the dorsal side. On the palmar side, the carpal bones form a narrow passage called the carpal tunnel. The flexor tendons slide through this tunnel in protective sheaths. This allows the tendons to move back and forth smoothly.

There are several types of movement permitted by the wrist. The most common are flexion and extension. Flexion is tilting the hand toward the palm. Extension is tilting the hand toward the back. Flexion is a very powerful movement. This is because the flexor muscles are stronger than the extensor muscles. You can also perform radial deviation and ulnar deviation. Radial deviation is moving the hand toward the thumb. Ulnar deviation is moving the hand toward the little finger. These movements happen at the radiocarpal and midcarpal joints.

Bone development in the wrist follows a specific timeline. This process is called ossification, which is the hardening of bone. In the first six months of an infant's life, certain bones begin to ossify. The capitate and hamate bones are the very first to do this. Because this pattern is consistent, doctors use wrist bone ossification to determine a child's bone age. This helps medical professionals understand how much a person has grown.

Medical issues can affect the wrist in many ways. A common injury is a distal radius fracture. This is a break in the bone at the end of the radius. Some conditions, like rheumatoid arthritis, can cause the hand to deviate at the wrist. Other common problems include carpal tunnel syndrome, ganglion cysts, and osteoarthritis. Even the name "wrist" has an interesting history. It comes from the Proto-Germanic word "wristiz." This root is associated with words meaning to twist or writhe. This makes sense, as the wrist is designed for twisting motions.