Muscle · Upper limb
Flexor carpi radialis: origin, insertion, action and innervation
The flexor carpi radialis runs from the medial epicondyle of the humerus to the second and third metacarpals. It flexes and abducts the wrist; median nerve.
Quick answer
- Latin name
- Musculus flexor carpi radialis
- Origin
- Medial epicondyle of the humerus, through the common flexor tendon
- Insertion
- Front of the bases of the second and third metacarpals (bones of the hand)
- Action
- Flexes and abducts (radially deviates) the wrist; weakly helps flex the elbow and pronate the forearm
- Innervation
- Median nerve (C6–C7)
- Blood supply
- Branches of the radial and ulnar arteries
See it on the 3D body
The flexor carpi radialis lit on the 3D forearm and hand, as in the forearm and hand quiz. Turn the body, peel the layers, tap any structure for its name.
The flexor carpi radialis is a superficial muscle on the front of the forearm that runs from the medial epicondyle of the humerus to the bases of the second and third metacarpals. It bends the wrist and tilts the hand toward the thumb, and it is supplied by the median nerve.
Where it is
The flexor carpi radialis belongs to the superficial layer of the anterior (flexor) compartment of the forearm. From the thumb side to the little-finger side, that layer holds the pronator teres, the flexor carpi radialis, the palmaris longus (when present) and the flexor carpi ulnaris. They all start together from the medial epicondyle.
Its belly runs diagonally down and outward across the forearm, toward the thumb side. In the lower half it becomes a long, round tendon. At the wrist crease, this tendon is easy to see and feel when you bend the wrist against resistance: it is the cord on the thumb side of the middle of the wrist. The radial artery lies just lateral to it, which is why the tendon is used as a guide to find the radial pulse.
The tendon does not pass through the carpal tunnel with the finger flexors. It runs in its own tunnel, through a split in the flexor retinaculum and along a groove on the trapezium, one of the carpal bones, before reaching the metacarpals.
Origin and insertion
- Origin: the common flexor tendon, which attaches to the medial epicondyle of the humerus.
- Insertion: the front (palmar surface) of the bases of the second and third metacarpals, mainly the second (see the bones of the hand).
What it does
- Flexion of the wrist. It bends the hand forward, working with the flexor carpi ulnaris and the palmaris longus.
- Abduction (radial deviation) of the wrist. It tilts the hand toward the thumb, working with the extensor carpi radialis longus and brevis on the back. Flexor and extensor cancel each other's bending action, so together they produce a pure sideways tilt, as when you cock a hammer before striking.
- Minor helper roles. Because it crosses the elbow and runs diagonally across the forearm, it can weakly help flex the elbow and pronate the forearm.
Innervation and blood supply
The flexor carpi radialis is supplied by the median nerve (roots C6 and C7), which runs down the middle of the forearm deep to it. The median nerve supplies every superficial forearm flexor except the flexor carpi ulnaris, which belongs to the ulnar nerve.
Its blood comes from branches of the radial and ulnar arteries, the two arteries of the forearm.
How to remember it
- Read the name. Flexor (bends), carpi (wrist), radialis (thumb side): a wrist flexor on the radius side.
- Second in line. Counting the superficial flexors from the thumb side (pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris), the flexor carpi radialis is number two.
- Pulse next door. The radial artery lies just lateral to the flexor carpi radialis tendon at the wrist.
- Not in the tunnel. Its tendon has its own channel through the flexor retinaculum, separate from the carpal tunnel.
Compare all the wrist flexors and extensors on the muscles of the forearm page, then find it in the arm and elbow quiz.
Frequently asked questions
What is the action of the flexor carpi radialis?
Wrist flexion and wrist abduction: it bends the hand forward and tilts it toward the thumb. It gives weak help with elbow flexion and pronation.
What nerve supplies the flexor carpi radialis?
The median nerve, from roots C6 and C7.
Where does the flexor carpi radialis insert?
On the front of the bases of the second and third metacarpals, mainly the second.
Does the flexor carpi radialis go through the carpal tunnel?
No. Its tendon runs in a separate channel through the flexor retinaculum, in a groove on the trapezium.
How do you find the flexor carpi radialis tendon?
Bend your wrist against resistance: it is the prominent tendon on the thumb side of the middle of the wrist crease, just medial to the radial pulse.
