Extensor Carpi Radialis Longus: Origin, Insertion, Action & Nerve

The Extensor Carpi Radialis Longus (ECRL) is a long, fusiform muscle located on the lateral side of the forearm. As its name suggests ("Longus"), it is longer than its partner, the "Brevis." It is one of the primary wrist extensors and plays a crucial role in stabilizing the hand during power grips.

[Image of Extensor Carpi Radialis Longus muscle anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	Distal one-third of the Lateral Supracondylar Ridge of the Humerus.
Insertion (Distal)	Dorsal surface of the base of the 2nd Metacarpal bone (Index finger).
Nerve Supply	Radial Nerve (C6, C7) - *before* it divides into deep/superficial branches.
Blood Supply	Radial Artery and Radial Recurrent Artery.
Primary Actions	Extension: Extends the wrist. Radial Deviation: Abducts the wrist (moves it toward the thumb side). Elbow Flexion: Weak assistance.

Deep Dive: Longus vs. Brevis

The ECRL and ECRB (Brevis) work together, but they have distinct anatomical features.

1. Origin Difference

The ECRL originates higher up on the arm (supracondylar ridge), while the ECRB originates lower down on the Lateral Epicondyle. This higher origin gives the ECRL slightly more leverage for elbow flexion, though it is still weak compared to the Brachioradialis.

2. Insertion Difference

The ECRL inserts on the 2nd Metacarpal (Index finger side), while the ECRB inserts on the 3rd Metacarpal (Middle finger). Because the ECRL insertion is further from the midline of the wrist, it is a more powerful Radial Deviator than the Brevis.

Physio Corner: Clinical Relevance

💪 Functional Fact: Make a fist and clench it hard. You will feel the ECRL and ECRB contract strongly on the back of your forearm. They extend the wrist to prevent the flexor muscles from "active insufficiency," allowing your fingers to grip tightly.

Palpation

Ask the patient to make a fist and radially deviate (cock the wrist up and towards the thumb). Palpate the fleshy muscle belly just distal to the lateral epicondyle. The ECRL is the most lateral/anterior of the extensor group, sitting right next to the Brachioradialis.

⚠️ Clinical Pathology: Intersection Syndrome
This is a painful condition where the muscle bellies of the thumb muscles (Abductor Pollicis Longus/Extensor Pollicis Brevis) cross over the tendons of the ECRL and ECRB. Friction at this "intersection" (about 4cm proximal to the wrist) causes crepitus (squeaking) and pain, distinct from De Quervain's tenosynovitis.

Manual Muscle Testing (MMT)

We test extension combined with radial deviation to isolate this muscle group.

Testing Tip: To bias the ECRL over the ECRB, perform the test with the elbow flexed. The ECRB is more active when the elbow is extended.

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Gravity)	Position: Sitting. Forearm pronated (palm down) and supported on a table. Wrist hanging off the edge. Action: Patient extends the wrist upwards and deviates towards the thumb (radial side). Resistance: Applied at the dorsum of the 2nd metacarpal, pushing down and towards the ulnar side (flexion + ulnar deviation). Grade 3: Full range against gravity. Grade 4/5: Holds against strong resistance.
Grade 2 (Gravity Eliminated)	Position: Forearm in neutral (mid-position, thumb up) resting on the table. Action: Patient extends the wrist (sliding the back of the hand along the table). Result: Full range of motion.
Grade 0, 1 (Palpation)	Action: Palpate the dorsum of the wrist at the base of the 2nd metacarpal (index finger ray). Cue: "Try to lift your hand back towards your thumb." Grade 1: Tendon tension felt. Grade 0: No activity.

Frequently Asked Questions

Why is ECRL usually spared in Tennis Elbow?

Tennis Elbow (Lateral Epicondylitis) primarily affects the ECRB because it originates directly from the epicondyle. The ECRL originates higher up on the supracondylar ridge, sparing it from the mechanical stress at the epicondyle.

Does ECRL help bend the elbow?

Yes, weakly. Because it crosses anterior to the axis of the elbow joint (originating on the supracondylar ridge), it has a slight moment arm for flexion, especially when the forearm is pronated.

What is the "Radial Nerve" relation?

The ECRL is usually the last muscle supplied by the main trunk of the Radial Nerve before it splits into the Superficial (Sensory) and Deep (Motor/PIN) branches. This means in high radial nerve injuries, ECRL might be affected, but in lower compressions (like Arcade of Frohse), it is spared.

Test Your Knowledge: ECRL Quiz

1. Where does the Extensor Carpi Radialis Longus originate?

2. Where does the ECRL insert?

3. Which nerve supplies the ECRL?

4. Besides extension, what is the secondary wrist action of ECRL?

5. Intersection Syndrome involves friction between ECRL/ECRB and which muscles?

6. Is ECRL primarily involved in "Tennis Elbow"?

7. Which muscle lies immediately lateral (or anterior) to the ECRL?

8. ECRL helps to stabilize the wrist during:

9. To differentiate ECRL from ECRB, you can test with the elbow:

10. The ECRL inserts on which aspect of the metacarpal?

References

• Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2018). Clinically Oriented Anatomy. 8th ed. Philadelphia: Wolters Kluwer.
• Standring, S. (2016). Gray's Anatomy: The Anatomical Basis of Clinical Practice. 41st ed. Elsevier.
• Kendall, F. P. (2005). Muscles: Testing and Function, with Posture and Pain. 5th ed. Lippincott Williams & Wilkins.