Carpal bones

Eight small bones make up your wrist.

These bones connect your hand to your arm. They help your wrist move in many ways. You can tilt your hand up or down. You can also move it side to side.

The bones work together to make these moves. Some bones move a little on their own. This helps your hand stay strong. These tiny bones are very important for your movement. Can you move your wrist now?

Your wrist is made of eight small bones. These are called carpal bones. They connect your hand to your forearm.

These bones help your wrist move. You can tilt your hand up or down. This is called flexion and extension. You can also move your hand side to side. This is called abduction and adduction.

The carpal bones work in two rows. The first row is near your arm. It has the scaphoid, lunate, triquetral, and pisiform bones. These bones move a little on their own. The second row is near your hand. This row is more rigid. It moves with the bones in your hand.

Ligaments help keep everything in place. Ligaments are tough parts that join bones together. They connect the carpal bones to each other. They also connect the bones to your arm.

These bones grow from cartilage after you are born. Some bones appear very early in life. The pisiform bone appears much later. It shows up after you are ten years old.

Your wrist is a very busy place. It is made of eight small bones called carpal bones. These bones connect your hand to your forearm. The names for these bones come from the Latin word carpus. This comes from a Greek word that also means wrist.

These bones are important for many tasks. They help your hand move in many directions. They also form a tunnel for nerves and tendons. This tunnel is called the carpal tunnel. It lets important parts travel to your fingers.

These eight bones work together in a special way. You can think of them as two rows or three columns. The first row is near your arm. It has the scaphoid, lunate, triquetral, and pisiform bones. These bones can move a little bit on their own. The second row is closer to your hand. This row is more rigid. It moves along with the bones of your hand.

Some bones, like the scaphoid, help keep the wrist stable. The bones are made of hard outer layers. Inside, they have a spongy tissue called cancellous tissue. This structure helps the wrist stay strong but flexible.

These bones do not appear all at once. They grow from cartilage after you are born. This way of growing is called ossification. The bones start appearing in a spiral pattern. The capitate and hamate bones appear first. The capitate can appear at 2.5 months old. The hamate often appears between 4 and 5.5 months. Other bones take much longer to grow. For example, the pisiform bone appears after ten years.

Many different movements happen at the wrist. You can tilt your hand toward your palm. This is called palmar flexion. You can also tilt it toward the back of your hand. This is called dorsiflexion. You can move your hand side to side too. Moving toward the thumb side is called abduction. Moving toward the pinky side is called adduction.

These movements happen around a central point. This point is the head of the capitate bone. Tough bands called ligaments hold all these bones together. They act like strong ropes to keep the joint steady.

Other animals have different wrist bones. Many animals called tetrapods have a carpus. In old fossil amphibians, the wrist had three rows of bones. Most mammals and reptiles have lost some bones. For example, many have lost the fifth distal carpal. Even birds have a very different wrist. A bird's wing has only two remaining carpals. The scaphoid in a mammal is like the radiale in a bird.

It is amazing how many ways nature builds a wrist.

The carpal bones are a group of eight small bones that form the human wrist, known as the carpus. This complex structure serves as the vital connection between the hand and the forearm. The terms "carpus" and "carpal" come from the Latin carpus and the Greek karpos, both meaning wrist. These bones are essential for human movement and protection. They articulate with the radial and ulnar heads to create a highly mobile condyloid joint. This joint allows for a wide range of motion. Additionally, the bones help provide attachment points for the thenar and hypothenar muscles. They also help form the rigid carpal tunnel. This tunnel protects the median nerve and the tendons of the anterior forearm muscles as they travel to the fingers.

To understand how they function, it is helpful to look at how they are organized. You can think of the eight bones as being arranged in two transverse rows. In this view, each row forms an arch that is convex proximally and concave distally. On the palmar side, the carpus is concave to form the carpal tunnel. This tunnel is covered by a structure called the flexor retinaculum.

Alternatively, clinicians often view the bones as three longitudinal columns. The radial scaphoid column includes the scaphoid, trapezium, and trapezoid. The lunate column consists of the lunate and the capitate. The ulnar triquetral column contains the triquetrum and the hamate. In this column model, the pisiform is seen as a sesamoid bone. A sesamoid bone is a small bone embedded within a tendon, specifically the tendon of the flexor carpi ulnaris.

The bones are divided into two distinct rows: the proximal and the distal rows. The proximal row is closer to the arm and includes the scaphoid, lunate, triquetral, and pisiform. These bones articulate with the radius and the distal carpal row. Because they connect to these mobile surfaces, they constantly adapt. Each bone in this row has a small amount of independent mobility. For example, the scaphoid helps with midcarpal stability by articulating with the trapezium and trapezoid. The distal row is located closer to the hand and is more rigid. This row moves together with the metacarpals. Most carpal bones have six surfaces. The palmar and dorsal surfaces are rough to allow for ligamentous attachment. The superior and inferior surfaces are articular surfaces used for joints.

Ligaments play a massive role in keeping these bones stable during movement. There are four main groups of ligaments in the wrist region. The first group unites the ulna and radius with the carpus. These include the ulnar and radial collateral ligaments, the palmar and dorsal radiocarpal ligaments, and the palmar ulnocarpal ligament.

The second group connects the carpal bones to each other. These are the intercarpal ligaments, such as the radiate carpal ligament. The third group connects the carpals to the metacarpals. Finally, the fourth group involves the intermetacarpal ligaments. These various bands of tissue ensure the bones stay in place while allowing for complex motions.

Wrist movement involves several specific types of motion. When the hand is in a straight position, the third finger aligns with the forearm. From this position, the hand can perform abduction, or radial deviation. This is a movement of about 15 degrees toward the radius. The opposite movement is adduction, or ulnar deviation, which is about 40 degrees toward the ulna. These movements occur around an axis passing through the head of the capitate bone.

The wrist also performs flexion and extension. Flexion tilts the hand toward the palm, while extension, or dorsiflexion, tilts it toward the back of the hand. The total range for these movements is 170 degrees. During radial abduction, the scaphoid tilts toward the palmar side. This allows the trapezium and trapezoid to move closer to the radius.

The development of these bones is a slow process that happens after birth. The carpal bones undergo ossification endochondrally, meaning they grow from within cartilage. The centers of ossification appear in a chronological spiral pattern. This process starts with the capitate and hamate during the first year of life. The capitate center can appear as early as 2.5 months. The hamate typically appears between 4 and 5.5 months. Other bones appear much later. For instance, the scaphoid and trapezoid often appear around 6 years of age. The pisiform is the last to arrive, appearing after ten years. Because this timing is so predictable, scientists can use it for forensic age estimation.

Finally, the carpus is a subject of great interest in evolutionary biology. The structure of the carpus varies widely among tetrapods, which are four-limbed animals. In primitive fossil amphibians like Eryops, the carpus had three rows of bones. These included a proximal row, a second row, and a distal row. Most modern vertebrates have undergone fusion or loss of these bones. For example, most mammals and reptiles have lost the fifth distal carpal. Birds have a very different structure. A modern bird's wing has only two remaining carpals. One is the radiale, which is similar to the mammalian scaphoid. This shows how the basic carpal blueprint has changed across different species throughout history.