The carpal bones are eight small, irregularly shaped bones that make up the wrist. They sit between the two forearm bones (the radius and ulna) and the long bones of the hand (the metacarpals), arranged in two neat rows of four. Together, they give the wrist its remarkable range of motion while keeping the joint stable enough to bear weight and absorb impact.
The Two Rows of Carpal Bones
The eight carpal bones are divided into a proximal row (closer to the forearm) and a distal row (closer to the fingers). Starting from the thumb side and moving toward the pinky, the proximal row contains the scaphoid, lunate, triquetrum, and pisiform. The distal row contains the trapezium, trapezoid, capitate, and hamate.
A common mnemonic for remembering all eight in order is “Some Lovers Try Positions That They Can’t Handle,” with each first letter matching a bone. There are dozens of variations, but the sequence stays the same: proximal row first (thumb side to pinky side), then distal row in the same direction.
What Each Bone Looks Like
The names of the carpal bones are descriptive, and knowing what they mean makes the anatomy easier to picture.
- Scaphoid: From the Greek for “boat.” It’s the largest bone in the proximal row, shaped like a curved hull, and sits right at the base of the thumb.
- Lunate: Named for its crescent or moon shape. It sits in the center of the proximal row, directly in line with the middle finger.
- Triquetrum: Means “three-cornered” in Latin. This pyramid-shaped bone sits on the pinky side of the proximal row.
- Pisiform: Latin for “pea-shaped.” This tiny, round bone sits on the palm side of the wrist, right on top of the triquetrum. You can feel it as a small bump at the base of your palm on the pinky side.
- Trapezium: A four-sided bone at the base of the thumb. It forms the joint that lets your thumb oppose your fingers.
- Trapezoid: The smallest bone in the distal row, wedge-shaped and tucked between the trapezium and capitate.
- Capitate: From the Latin for “head.” It’s the largest of all eight carpal bones, sitting right in the center of the wrist, and its rounded top fits into a socket formed by the scaphoid and lunate.
- Hamate: Named for its hook. A bony projection called the “hook of the hamate” sticks out on the palm side and serves as an anchor point for ligaments and muscles.
The Pisiform Is Unusual
The pisiform stands apart from the other seven carpal bones. It’s classified as a sesamoid bone, meaning it develops within a tendon, specifically the tendon of the forearm muscle that flexes the wrist toward the pinky side. Because of this, the pisiform doesn’t participate directly in wrist movement the way the other carpal bones do. It articulates with only one bone (the triquetrum) and mainly serves as a leverage point, increasing the pulling power of the tendon it’s embedded in.
The pisiform is also the last carpal bone to harden. Its ossification center doesn’t appear until roughly age 8 to 10, and the process is usually complete by age 12. In four-legged animals, the pisiform plays a much larger structural role, functioning similarly to the heel bone in the human foot.
How the Carpal Bones Connect
The proximal row articulates with the radius (the larger forearm bone on the thumb side) to form the main wrist joint. The ulna doesn’t actually contact the carpal bones directly. Instead, a disc of cartilage sits between the ulna and the proximal row, cushioning that side of the wrist.
The distal row connects to the five metacarpal bones through a series of tight-fitting joints reinforced by strong ligaments. These joints are far less mobile than the main wrist joint. They form a rigid, stable unit that transfers force efficiently from the hand into the wrist and forearm, which is why you can push, grip, and carry heavy loads without the base of your hand collapsing.
Between the two rows themselves, the bones glide against each other in small, controlled movements. A dense web of ligaments holds the carpal bones together. Some of the most important run between the scaphoid and lunate, connecting the two central bones of the proximal row. Other ligaments form V-shaped patterns across the back of the wrist, linking the radius to the triquetrum and reinforcing the entire structure. These ligaments don’t just prevent the bones from separating. They guide how the rows move relative to each other during wrist flexion, extension, and side-to-side tilting.
When Carpal Bones Develop in Children
At birth, the carpal bones are made entirely of cartilage and don’t show up on a standard X-ray. They harden into bone gradually throughout childhood, following a predictable sequence that doctors sometimes use to estimate a child’s skeletal maturity.
The capitate ossifies first, with a bone center appearing as early as 3 to 4 months of age. The hamate follows shortly after, around 5 to 12 months. From there, the remaining bones appear roughly one per year: the triquetrum around age 2 to 3, the lunate around age 3 to 4, the scaphoid around age 4 to 5, and the trapezium and trapezoid around age 4 to 6. The pisiform comes last, not beginning to harden until around age 8 to 10. Girls tend to reach each milestone a few months to a year earlier than boys.
This slow, staggered development is one reason wrist injuries in young children can be tricky to diagnose on X-rays. A fracture through cartilage that hasn’t yet ossified may not be visible, which is why doctors sometimes rely on physical examination and follow-up imaging rather than a single X-ray.
Why the Scaphoid Matters Most in Injuries
Of all eight carpal bones, the scaphoid is the most commonly fractured. It breaks when you fall onto an outstretched hand, which drives force directly into the bone’s narrow waist. Scaphoid fractures are notorious for being missed on initial X-rays because the fracture line can be hairline-thin. Pain in the “anatomical snuffbox,” the small hollow on the back of your wrist near the base of the thumb, is the classic sign.
The scaphoid also has a tricky blood supply. Blood enters mainly through one end of the bone, so a fracture across the middle can cut off circulation to the other end. Without adequate blood flow, the bone fragment can die, a complication that makes prompt diagnosis and treatment important. This is why a wrist injury with snuffbox tenderness is often treated as a fracture until proven otherwise, even if the first X-ray looks normal.
The hamate’s hook is another vulnerable spot, particularly in athletes who grip bats, rackets, or golf clubs. Repeated impact against the hook can cause a stress fracture that produces pain deep in the palm on the pinky side.
The Carpal Tunnel Runs Through Them
The carpal bones form three sides of the carpal tunnel, the narrow passageway on the palm side of your wrist. The scaphoid and trapezium form the thumb-side wall, while the pisiform and the hook of the hamate form the pinky-side wall. A tough band of tissue called the flexor retinaculum stretches across the top, completing the tunnel’s roof.
Nine tendons and the median nerve pass through this small space. When the tunnel narrows or its contents swell, the nerve gets compressed, producing the numbness, tingling, and weakness known as carpal tunnel syndrome. The rigid bony walls mean there’s very little room for expansion, which is why even mild swelling can cause symptoms.