Extensor Carpi Radialis Longus

The extensor carpi radialis longus is a superficial muscle of the posterior compartment of the forearm. It primarily extends and abducts the wrist. Positioned lateral to the extensor carpi radialis brevis, it contributes to wrist movements and provides dynamic stability during grip and lifting activities.

Location

The extensor carpi radialis longus is located on the lateral side of the posterior forearm. It emerges from the lateral supracondylar ridge of the humerus and runs down to the base of the second metacarpal bone.

Structure

The muscle has a long, fusiform belly that narrows into a strong tendon distally. It lies superficial throughout its course and is partly covered by the brachioradialis in the proximal forearm.

• Origin: Lateral supracondylar ridge of the humerus (just above the lateral epicondyle).
• Insertion: Dorsal surface of the base of the second metacarpal bone.
• Fiber Direction: Runs obliquely from proximal-lateral to distal-medial across the forearm.
• Tendon Path: The tendon passes under the extensor retinaculum within the second dorsal compartment of the wrist.

Function

The extensor carpi radialis longus contributes to:

• Wrist Extension: Extends the hand at the wrist, particularly when the fingers are flexed.
• Wrist Abduction (Radial Deviation): Works with the flexor carpi radialis to abduct the wrist.
• Grip Stabilization: Stabilizes the wrist during gripping actions by counteracting flexion forces.

Innervation

The muscle is innervated by the radial nerve (C6–C7), specifically from a branch before the radial nerve divides into superficial and deep branches.

Blood Supply

• Radial artery: Primary arterial supply.
• Radial recurrent artery: May contribute proximally.

Relations

In the upper forearm, the extensor carpi radialis longus lies adjacent to the brachioradialis. As it descends, it runs lateral to the extensor carpi radialis brevis. The radial nerve passes deep to the muscle near its origin.

Surface Anatomy

The muscle and its tendon can often be seen or palpated on the lateral side of the forearm, especially during active wrist extension and abduction. Its tendon lies just medial to the brachioradialis at the wrist.

Development

The extensor carpi radialis longus develops from the extensor muscle mass of the posterior forearm bud, which originates from paraxial mesoderm during embryogenesis. Its radial nerve innervation is consistent with its origin from the dorsal muscle group.

Anatomical Variations

• May have accessory slips to other metacarpals or to the extensor expansions.
• Fusion with the extensor carpi radialis brevis or brachioradialis may occur proximally.

Clinical Significance

• Lateral Epicondylitis (Tennis Elbow): Though more associated with the extensor carpi radialis brevis, overuse of the longus can contribute to lateral elbow pain.
• Tendon Transfers: Its tendon may be used in reconstructive surgery due to its strength and accessibility.
• Wrist Instability: Weakness or damage to this muscle can impair wrist extension and radial deviation, affecting grip strength.

Comparative Anatomy

In some primates and quadrupeds, the extensor carpi radialis longus is more developed due to its role in limb support and locomotion. In humans, it has evolved to assist in precision grip and coordinated wrist movement.