The wrist is a complex joint connecting your forearm to your hand, made up of eight small bones, two major arteries, three nerves, dozens of ligaments, and multiple tendons all packed into a surprisingly small space. It’s not a single joint but a collection of joints working together to let you bend, twist, and angle your hand in nearly every direction.
The Eight Carpal Bones
The core of the wrist is a cluster of eight small bones called carpal bones, arranged in two rows. The row closer to your forearm (the proximal row) contains the scaphoid, lunate, triquetrum, and pisiform. The row closer to your fingers (the distal row) holds the trapezium, trapezoid, capitate, and hamate. These bones are roughly pebble-sized and fit together like an irregular mosaic, creating a structure that’s both flexible and strong enough to bear weight when you push yourself up from a chair or do a pushup.
Interestingly, you aren’t born with these bones fully formed. In infants, the carpal bones are still cartilage and gradually harden (ossify) over childhood. The capitate and hamate are the first to appear, hardening as early as six months of age. The pisiform is the last, not fully ossified until around age 10 in girls and 14 in boys. This is why doctors sometimes use a wrist X-ray to estimate a child’s skeletal age.
How the Wrist Moves
The main joint of the wrist, the radiocarpal joint, forms where the larger forearm bone (the radius) meets the scaphoid, lunate, and triquetrum. This joint works like a shallow ball-and-socket, allowing four primary movements: bending your hand forward (flexion), bending it backward (extension), tilting it toward your thumb (radial deviation), and tilting it toward your pinky (ulnar deviation).
Normal range of motion is about 73 degrees of flexion, 71 degrees of extension, 19 degrees of radial deviation, and 33 degrees of ulnar deviation. The wrist also plays a role in rotating your forearm, contributing to roughly 140 degrees of palm-up rotation and 60 degrees of palm-down rotation. These movements don’t come from one joint alone. The joints between the two rows of carpal bones and between the carpal bones themselves all contribute, which is why wrist motion feels so fluid compared to, say, an elbow hinge.
Ligaments That Hold It Together
With so many small bones packed together, the wrist relies heavily on ligaments to stay stable. These fall into two categories. Extrinsic ligaments connect the carpal bones to the forearm bones above or the hand bones below, acting like guy-wires anchoring the wrist to the rest of the arm. Intrinsic ligaments link the carpal bones to each other, keeping the two rows aligned during movement.
Two of the most clinically important intrinsic ligaments are the scapholunate and lunotriquetral ligaments, which bind key bones in the proximal row. A tear in the scapholunate ligament is one of the most common serious wrist injuries and can lead to chronic instability if untreated. On the extrinsic side, the radiolunate and radioscaphocapitate ligaments are major stabilizers that prevent the carpal bones from shifting out of position under load.
Nerves Passing Through the Wrist
Three major nerves travel through or around the wrist to supply sensation and muscle control to the hand. The median nerve passes through the carpal tunnel, a narrow channel formed by the carpal bones on three sides and a tough band of tissue (the transverse carpal ligament) on top. It controls muscles at the base of the thumb and provides sensation to the thumb, index, middle, and part of the ring finger.
The ulnar nerve takes a different path, traveling through a small depression called Guyon’s canal between the pisiform bone and the hook of the hamate. It supplies sensation and motor control to the pinky side of the hand. The radial nerve runs along the thumb side of the wrist and primarily provides sensation to the back of the hand.
The Carpal Tunnel
The carpal tunnel deserves its own mention because it’s where one of the most common nerve problems in the body occurs. This narrow passageway holds nine flexor tendons (the cords that bend your fingers) plus the median nerve. Because the tunnel has rigid walls made of bone and ligament, there’s very little room to spare. If any of the nine tendons become inflamed from repetitive use, fluid retention, or other causes, they swell and compress the median nerve. The result is carpal tunnel syndrome: tingling, numbness, and weakness in the thumb, index, and middle fingers.
Blood Supply
Two major arteries deliver blood to the wrist and hand. The radial artery runs along the thumb side of the wrist, which is where you feel your pulse. The ulnar artery runs along the pinky side, passing through Guyon’s canal alongside the ulnar nerve. At the wrist, both arteries send off small branches that form the palmar carpal arch, a network supplying the carpal bones and joints directly.
Once these arteries enter the hand, they form two loops called the superficial and deep palmar arches. The superficial arch is primarily fed by the ulnar artery and sits just beneath the skin of the palm. The deep arch is mainly supplied by the radial artery and lies deeper, beneath the tendons. This dual-arch system provides backup blood flow. If one artery is compressed or injured, the other can often keep the hand supplied through these interconnected loops.
The TFCC: A Built-In Cushion
On the pinky side of the wrist sits a structure called the triangular fibrocartilage complex, or TFCC. Think of it as a small, disc-shaped cushion wedged between the end of the smaller forearm bone (the ulna) and two carpal bones (the lunate and triquetrum). It absorbs load on that side of the wrist and stabilizes the joint where the two forearm bones meet. The TFCC is actually a collection of several components: a cartilage disc, multiple ligaments, and a tendon sheath, all working together. Tears in the TFCC are a common cause of pain on the pinky side of the wrist, especially after a fall on an outstretched hand or from repetitive twisting motions.
Why the Wrist Is Injury-Prone
The wrist’s complexity is also its vulnerability. Eight bones, dozens of ligaments, tendons running through tight tunnels, and nerves squeezed into narrow canals all create opportunities for things to go wrong. Falls are the most common culprit. When you catch yourself with an outstretched hand, the force travels directly into the carpal bones and the radius. The scaphoid, sitting right at the base of the thumb, is the most frequently fractured carpal bone and is notorious for poor blood supply, which can make healing slow.
Repetitive strain is the other major category. Activities that involve sustained gripping, typing, or vibration can inflame tendons inside the carpal tunnel or irritate the TFCC. Because the wrist’s internal spaces are so tight, even small amounts of swelling can produce noticeable symptoms like pain, numbness, or weakness in the hand.