Each human hand contains 27 bones, divided into three groups: 8 small wrist bones (carpals), 5 palm bones (metacarpals), and 14 finger bones (phalanges). Together, these bones give your hand its remarkable combination of strength and fine motor control. Beyond those 27, most people also have a handful of tiny extra bones called sesamoids embedded in tendons near certain joints.
The 8 Carpal Bones (Wrist)
The carpal bones are eight small, irregularly shaped bones arranged in two rows of four at the base of your hand. They sit between your forearm bones and your palm, forming what you think of as your wrist.
The row closest to your forearm (proximal row) contains the scaphoid, lunate, triquetral, and pisiform. The row closer to your fingers (distal row) contains the trapezium, trapezoid, capitate, and hamate. These bones don’t move independently the way finger bones do. Instead, they shift slightly against each other to let your wrist bend, extend, and rotate. The tight arrangement and strong ligaments connecting them provide a stable base that transfers force between your arm and hand.
The scaphoid is the most commonly fractured carpal bone, accounting for roughly 60% of all carpal fractures. It typically breaks when you catch yourself during a fall with an outstretched hand. Scaphoid fractures can be tricky because the pain sometimes feels mild, leading people to mistake it for a sprain.
The 5 Metacarpal Bones (Palm)
The metacarpals are the five long bones that form the palm of your hand. You can feel them by pressing on the back of your hand: there’s one running behind each knuckle. They’re numbered one through five, starting at the thumb side. The first metacarpal connects to your thumb, the second to your index finger, the third to your middle finger, the fourth to your ring finger, and the fifth to your pinkie.
Each metacarpal has a base (which connects to a carpal bone), a shaft, and a rounded head that forms your knuckle. Metacarpal fractures are the second most common hand fracture, making up about 34% of all hand fractures in adults. A “boxer’s fracture,” one of the most frequent hand injuries, is a break at the neck of the fifth metacarpal, usually from punching something with a closed fist.
The 14 Phalanges (Fingers)
Your fingers contain 14 bones called phalanges. Each of the four fingers has three: a proximal phalanx (closest to the palm), a middle phalanx, and a distal phalanx (the fingertip bone just behind the nail). The thumb is different. It has only two phalanges, a proximal and a distal, with no middle bone. This shorter structure, combined with the thumb’s unique joint at its base, is part of what allows the thumb to oppose the other fingers for gripping and pinching.
Phalanx fractures are the most common hand fractures overall, accounting for 54% of all hand fractures in adults. The fingertip bone is especially vulnerable because it’s exposed at the end of each finger, and crush injuries from doors or tools are a frequent cause.
How These Bones Connect: The Joints
The joints between hand bones have specific names based on which bones they connect, and each joint allows a different range of motion.
- Carpometacarpal (CMC) joints are where the metacarpals meet the carpal bones. Most of these joints are nearly rigid, which keeps the palm stable. The major exception is the thumb’s CMC joint at the base of the thumb, which sits on the trapezium bone and can bend, extend, swing away from the hand, and rotate. This freedom of movement is what makes your thumb opposable.
- Metacarpophalangeal (MCP) joints are your knuckles, where each metacarpal meets a finger bone. These allow you to bend and straighten your fingers and spread them apart.
- Proximal interphalangeal (PIP) joints are the middle joints of each finger (the first bend below the knuckle). They work like hinges, bending in only one direction.
- Distal interphalangeal (DIP) joints are the joints nearest your fingertips, just below the nail. They’re also simple hinges. The thumb has a single interphalangeal joint instead of a PIP and DIP, because it only has two phalanges.
Sesamoid Bones: The Hidden Extras
In addition to the 27 standard bones, your hand contains small, seed-shaped bones called sesamoids. These are embedded within tendons near certain joints, and they act like built-in pulleys, reducing friction and giving tendons better leverage.
Everyone has two sesamoid bones at the knuckle joint of the thumb. Beyond that, the number varies from person to person. A large multicenter study found that about 73% of people have a sesamoid at the pinkie knuckle, about 43% have one at the index finger knuckle, and roughly 22% have one at the thumb’s interphalangeal joint. Sesamoids at the middle and ring finger knuckles are rare. In total, a majority of people have about five sesamoid bones per hand, though the exact count differs between individuals.
How Hand Bones Develop
Babies aren’t born with fully hardened hand bones. Bone development starts during embryonic life, but the carpal bones begin as soft cartilage and gradually harden (ossify) over childhood. The capitate and hamate are the first to appear, beginning to ossify around six months of age. The triquetral follows around age three, the lunate around four, and the scaphoid around five. The trapezium and trapezoid show up around age six. The pisiform is the last carpal bone to harden, typically not appearing on an X-ray until around age twelve.
This predictable sequence is so reliable that doctors sometimes use a hand X-ray to estimate a child’s skeletal age. Girls generally reach each ossification milestone earlier than boys by several months to a year. The entire process of hand bone development isn’t fully complete until adolescence.