Carpal bones

The carpal bones are the eight small bones that make up the wrist (carpus) that connects the hand to the forearm. They are an important part of our bodies because they help us move our wrists in many directions. The terms "carpus" and "carpal" come from old languages—Latin and Greek—and they mean "wrist."

In all four-legged animals, including humans, the carpus is the only group of bones in the wrist. These bones sit between the two bones of the lower arm, the radius and ulna, and the bones of the hand, called the metacarpus. The carpal bones help the wrist bend and turn, making our hands very useful for different tasks.

Structure

The eight carpal bones in your wrist can be thought of as two rows or three columns. When you look at them as two rows, each row forms an arch. The top row includes the scaphoid, lunate, triquetral, and pisiform bones. These bones move a lot and help your wrist stay stable. The bottom row is stiffer and moves with the bones of your hand.

Scientists often think of these bones as three columns: the radial column (scaphoid, trapezium, and trapezoid), the lunate column (lunate and capitate), and the ulnar column (triquetrum and hamate). The pisiform bone is special because it sits inside a tendon. The wrist is stronger when you bend it forward than when you bend it backward, thanks to its ligaments and the way the bones fit together. Most carpal bones have six sides, with some sides rough for ligaments and others smooth for moving against each other. Inside, they are made of a spongy tissue wrapped in a tough outer layer.

Sometimes extra small bones can be found in the wrist, but only a few are well-known.

Development

The carpal bones form from within the cartilage after a child is born. Small centers of bone start to appear in a special order, beginning with the capitate and hamate bones in the first year of life. Later, other bones in the wrist, like the ulnar and radial bones, also start to form. This pattern of growth helps scientists estimate a person's age.

Function

The carpal bones in our wrists help us move our hands in many ways. They connect to the arm bones, called the ulna and radius, and work together with special bands of tissue called ligaments. These ligaments hold the bones in place and help our wrists move smoothly.

Our hands can move in several directions. We can move our hands towards our body (palmar flexion) or away from our body (dorsiflexion). We can also move our hands to the side towards the thumb (radial abduction) or towards the little finger (ulnar adduction). All these movements help us do everyday tasks like writing, playing, and grabbing objects.

Other animals

The structure of the wrist, or carpus, looks different across various animals. In early amphibians, like Eryops, the wrist had three rows of bones. Over time, most animals, including modern amphibians, mammals, and reptiles, have lost or fused some of these bones, ending up with fewer wrist bones.

Birds, for instance, have just two wrist bones left in their wings. In some animals like macropods, certain wrist bones fuse together. Interestingly, in crustaceans, the term "carpus" refers to parts of their claws or pincers.

See also: Carpus and tarsus of land vertebrates

Etymology

The word "carpus" comes from Latin, and it is derived from the Greek word καρπὁς, meaning "wrist". The root "carp-" translates to "pluck", an action that our wrists help us do.