Flexor Carpi Radialis: Origin, Insertion, Action, Nerve & Clinical Testing

The Flexor Carpi Radialis (FCR) is a superficial muscle of the anterior forearm. It is a slender muscle that runs diagonally across the forearm from the elbow to the base of the thumb. It is a key landmark for finding the radial pulse and is one of the primary flexors of the wrist.

[Image of Flexor Carpi Radialis muscle anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	Medial Epicondyle of the Humerus (via the Common Flexor Tendon).
Insertion (Distal)	Base of the 2nd Metacarpal (and a slip to the 3rd Metacarpal).
Nerve Supply	Median Nerve (C6, C7).
Blood Supply	Radial Artery.
Primary Actions	Flexion: Flexes the wrist joint. Radial Deviation: Abducts the wrist (moves it toward the thumb side). Elbow Flexion: Very weak assistance.

Deep Dive: The Guide to the Pulse

The FCR is anatomically significant not just for movement, but as a landmark.

1. The Radial Artery Guide

In the distal forearm (near the wrist), the tendon of the FCR is the most lateral prominent tendon. The Radial Artery lies immediately lateral to this tendon. If you can find the FCR tendon, you can easily locate the pulse just to the thumb-side of it.

2. The Tunnel

Unlike the other flexor tendons that pass through the Carpal Tunnel, the FCR travels through its own separate tunnel within the flexor retinaculum. It passes through a groove on the Trapezium bone, which can sometimes be a site of tenosynovitis (inflammation).

Physio Corner: Clinical Relevance

💪 Functional Fact: The FCR works in synergy with the Extensor Carpi Radialis (Longus/Brevis) to perform pure Radial Deviation. When they contract together, their flexion and extension forces cancel out, leaving only the deviation.

Palpation

Ask the patient to flex their wrist and deviate toward the thumb against resistance. The tendon will pop up clearly on the anterior wrist, just medial to the radial styloid. It is the most lateral of the wrist flexor tendons.

⚠️ Clinical Pathology: Golfer's Elbow
Since the FCR originates from the common flexor tendon on the medial epicondyle, overuse (repetitive wrist flexion) contributes to Medial Epicondylitis (Golfer's Elbow). Pain is felt at the inner elbow during resisted wrist flexion.

Manual Muscle Testing (MMT)

To isolate the FCR, we must combine flexion with radial deviation.

Testing Tip: Ensure the fingers are relaxed. If the patient makes a tight fist, the Flexor Digitorum muscles may substitute for a weak FCR.

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Gravity)	Position: Sitting. Forearm supinated (palm up) on a table. Wrist hanging off the edge. Action: Patient flexes the wrist and deviates toward the thumb (up and in). Resistance: Applied at the base of the 2nd metacarpal (thenar eminence), pushing down (extension) and toward the pinky (ulnar deviation). Grade 3: Full range against gravity. Grade 4/5: Holds against resistance.
Grade 2 (Gravity Eliminated)	Position: Forearm in neutral (mid-position, thumb up) resting on table. Action: Patient flexes the wrist (sliding across table). Result: Full range of motion.
Grade 0, 1 (Palpation)	Action: Palpate the tendon at the anterior wrist, lateral to Palmaris Longus. Cue: "Try to bend your wrist forward and toward your thumb." Grade 1: Tendon tension felt. Grade 0: No activity.

Frequently Asked Questions

Does FCR go through the Carpal Tunnel?

No. While it passes under the superficial layer of the Flexor Retinaculum, it travels in a separate compartment (its own tunnel) lateral to the main Carpal Tunnel. Therefore, it is not usually involved in Carpal Tunnel Syndrome compression.

How do I differentiate FCR from Palmaris Longus?

Palmaris Longus is more medial and central. FCR is lateral (closer to the thumb). Also, FCR inserts into bone (metacarpal), while Palmaris Longus inserts into the soft tissue of the palm (Palmar Aponeurosis).

Does FCR flex the elbow?

Yes, but very weakly. Because it originates on the Medial Epicondyle, it crosses the elbow joint anteriorly, but its leverage is insignificant compared to Brachialis or Biceps.

Test Your Knowledge: FCR Quiz

1. Where does the Flexor Carpi Radialis originate?

2. Which nerve supplies the FCR?

3. Where does the FCR insert?

4. The FCR tendon is a landmark for finding which pulse?

5. Besides flexion, what is the other primary action of FCR?

6. Does the FCR pass through the Carpal Tunnel?

7. Which muscle works with FCR to produce pure Radial Deviation?

8. Overuse of the FCR at its origin contributes to:

9. To test MMT Grade 5, you apply resistance towards:

10. True or False: FCR is superficial to the Flexor Digitorum Superficialis.

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.
• Magee, D. J. (2014). Orthopedic Physical Assessment. 6th ed. Elsevier.