Muscle · Upper limb
Extensor carpi radialis longus: origin, insertion, action and innervation
The extensor carpi radialis longus runs from the humerus above the elbow to the second metacarpal. It extends and abducts the wrist; radial nerve.
Quick answer
- Latin name
- Musculus extensor carpi radialis longus
- Origin
- Lower third of the lateral supracondylar ridge of the humerus and the lateral intermuscular septum
- Insertion
- Back of the base of the second metacarpal (bones of the hand)
- Action
- Extends and abducts (radially deviates) the wrist; weakly helps flex the elbow
- Innervation
- Radial nerve (C6–C7)
- Blood supply
- Radial artery and radial recurrent artery
See it on the 3D body
The extensor carpi radialis longus 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 extensor carpi radialis longus is a long muscle on the thumb side of the back of the forearm, running from the lower humerus, just above the elbow, to the base of the second metacarpal. It extends the wrist and tilts it toward the thumb, and it is supplied by the radial nerve.
Where it is
The muscle lies in the superficial layer of the posterior (extensor) compartment of the forearm, on its lateral, thumb side. Its fleshy belly is in the upper third of the forearm, tucked between the brachioradialis in front and its shorter twin, the extensor carpi radialis brevis, behind and below it.
Halfway down the forearm, the belly gives way to a long, flat tendon. At the wrist, this tendon runs in a groove on the back of the lower radius, in the second extensor compartment under the extensor retinaculum, side by side with the tendon of the brevis. On the way it is crossed by the thumb muscles that come out from deeper in the forearm. It ends on the back of the hand at the base of the index finger's metacarpal.
The name describes it: extensor (it straightens), carpi (of the wrist), radialis (on the radius side), longus (the longer of two).
Origin and insertion
- Origin: the lower third of the lateral supracondylar ridge of the humerus, just above the lateral epicondyle, and the neighboring lateral intermuscular septum.
- Insertion: the back (dorsal surface) of the base of the second metacarpal, the bone of the index finger (see the bones of the hand).
Note the origin: most forearm extensors start on the lateral epicondyle through a common tendon. The longus starts higher, on the ridge above it, like the brachioradialis.
What it does
- Extension of the wrist. It bends the hand back at the wrist, working with the extensor carpi radialis brevis and the extensor carpi ulnaris.
- Abduction (radial deviation) of the wrist. It tilts the hand toward the thumb side, working with the flexor carpi radialis. When both contract, their bending actions cancel out and only the tilt remains.
- Steadying the wrist for a grip. When you make a tight fist, the finger flexors would also bend the wrist. The wrist extensors contract to hold it slightly extended, which gives the fingers a stronger grip.
- Weak elbow flexion. Because it crosses the front of the elbow axis, it adds a little to bending the elbow.
Innervation and blood supply
The extensor carpi radialis longus is supplied by the radial nerve (roots C6 and C7). It gets its branch from the main trunk of the radial nerve above the elbow, before the nerve divides into its superficial and deep branches. The brevis, by contrast, is usually supplied by the deep branch.
Its blood comes from the radial artery and the radial recurrent artery.
How to remember it
- Longus starts higher. The longus begins on the supracondylar ridge; the brevis begins lower, on the lateral epicondyle.
- Index for longus, middle for brevis. The longus ends on the second metacarpal, the brevis on the third.
- Two radial wrist muscles, one on each side. The flexor carpi radialis on the front and the extensor carpi radialis longus on the back both tilt the hand toward the thumb.
- Radial nerve for the back. All muscles of the back of the forearm are supplied by the radial nerve or its deep branch.
See where it fits among the extensors on the muscles of the forearm page, then find it on the 3D arm in the arm and elbow quiz.
Frequently asked questions
What is the action of the extensor carpi radialis longus?
It bends the hand back at the wrist and tilts it toward the thumb. It also holds the wrist steady when you grip, and gives a little help in bending the elbow.
Where does the extensor carpi radialis longus insert?
On the back of the base of the second metacarpal, the bone of the index finger.
What nerve supplies the extensor carpi radialis longus?
The radial nerve (C6 and C7), from its main trunk above the elbow.
What is the difference between the extensor carpi radialis longus and brevis?
The longus starts higher, on the supracondylar ridge of the humerus, and ends on the second metacarpal. The brevis starts on the lateral epicondyle and ends on the third metacarpal. Both extend and abduct the wrist.
