Anatomy Guide › Upper limb
Radius
Hold your arm out palm-up: the radius is the forearm bone on the thumb side. It runs from a small round head just below the elbow down to a broad base that forms most of the wrist joint. Its name comes from the Latin for a wheel's spoke, and the comparison is apt, because the radius is the bone that rotates. When you turn your palm down, the radius pivots and crosses over the stationary ulna like the hands of a clock; turn your palm up and it swings back parallel. Doorknobs, screwdrivers, and steering wheels all work because of this motion.
At the elbow, the radial head is a little disc that spins in place against the humerus and ulna, held by a ring-shaped ligament. In young children the head is not fully formed, and a sharp pull on a toddler's hand can slip it out of that ring — 'nursemaid's elbow,' one of the most common childhood joint injuries and, happily, one of the easiest to fix.
At the wrist end, the radius widens dramatically to carry the hand: the scaphoid and lunate bones sit directly against it. This is also where the bone meets its most frequent misfortune. When people trip and catch themselves on an outstretched palm, the force rams the wrist into the radius, and the resulting distal radius fracture is one of the most common fractures in emergency medicine at every age — from skate parks to icy sidewalks.
In Anamo, the radius defines the thumb-side lane of the forearm. Its neighbors — scaphoid below, radial artery alongside, and the extensor muscles that cross it — make it a natural stepping-stone guess when the heat map trends toward the wrist.
- Named after the Latin for a wheel's spoke
- Rotates over the ulna to turn the palm up and down
- Forms most of the wrist joint with the scaphoid and lunate
- Its lower end is one of the most commonly fractured sites in the body
Think you could find the radius on a 3D model? Play Anamo and test yourself — every guess is color-coded by how close it lands to the mystery structure.