Flexor Carpi Radialis Muscle Anatomy Overview

The flexor carpi radialis muscle (FCR) is a long fusiform muscle located medial to the pronator teres muscle. In the middle of the forearm, its fleshy belly is replaced by a long, flattened tendon that becomes cord-like as it approaches the wrist.

It’s located in the superficial layer of the anterior compartment of the forearm along with:

1. Pronator teres,
2. Palmaris longus,
3. Flexor carpi ulnaris.

See Also: Forearm Muscles Anatomy & Function

The flexor carpi radialis produces flexion (when acting with the flexor carpi ulnaris) and abduction of the wrist (when acting with the extensors carpi radialis longus and brevis). When acting alone, the FCR produces a combination of flexion and abduction simultaneously at the wrist so that the hand moves anterolaterally.

To reach its distal attachment, the flexor carpi radialis tendon passes through a canal in the lateral part of the flexor retinaculum and through a vertical groove in the trapezium in its own synovial tendinous sheath of the flexor carpi radialis. The FCR tendon is a good guide to the radial artery, which lies just lateral to it.

Anatomy of the Flexor Carpi Radialis

Origin

The flexor carpi radialis originates from the medial epicondyle of the humerus. This common flexor origin is a critical point of attachment for several forearm muscles, highlighting its importance in upper limb movements.

Insertion

The tendon of the flexor carpi radialis inserts into the base of the 2nd metacarpal. This distal attachment plays a significant role in the muscle’s ability to facilitate precise movements of the wrist.

Action

The primary actions of the flexor carpi radialis are:

• Flexion of the Wrist: When acting in concert with the flexor carpi ulnaris, the FCR is a powerful flexor of the wrist.
• Abduction of the Wrist: In conjunction with the extensors carpi radialis longus and brevis, the FCR abducts the wrist.
• Combined Flexion and Abduction: Acting alone, the FCR produces simultaneous flexion and abduction, moving the hand anterolaterally.

Innervation

The flexor carpi radialis is innervated by the median nerve, specifically from the C6 and C7 nerve roots.

Arterial Supply

The ulnar artery provides the primary blood supply to the flexor carpi radialis, ensuring it receives the necessary nutrients and oxygen for optimal performance.

To assess the functionality of the flexor carpi radialis, ask the patient to flex their wrist against resistance. A normally functioning FCR will produce a visible and palpable tendon. This simple test can help diagnose potential nerve or muscle pathologies affecting the forearm.

See Also: Medial Epicondylitis

Flexor Carpi Radialis Brevis Anomalous Muscle

The flexor carpi radialis brevis (FCRB) is a rare anomalous muscle of the wrist. The incidence of the FCRB has been reported to be 2.6% to 7.5%. The FCRB originates from the lower one-third of the radius on its volar surface, or volo-radial border between the origin of the FPL and the insertion of the PQ, and it inserts into the base of the second or third metacarpal.

But, its insertion is subject to frequent variations, and may be into any metacarpal base except the first or fifth, and radial side carpal bones, such as the scaphoid, trapezium, trapezoid, and capitate) The FCRB is innervated by the anterior interosseous nerve.

While the FCR is superficial to the deep fascia in the same plane with the palmaris longus, the FCRB is located in the deep compartment, and occupies the space between the FPL and the BR, superficial to the PQ.

References & More

1. Moore, K. L., & Dalley, A. F. (2013). Clinically Oriented Anatomy. Lippincott Williams & Wilkins.
2. Netter, F. H. (2014). Atlas of Human Anatomy. Elsevier Health Sciences.
3. Schmidt HM. Clinical anatomy of the m. flexor carpi radialis tendon sheath. Acta Morphol Neerl Scand. 1987;25(1):17-28. PMID: 2449801. Pubmed
4. Erçakmak Güneş B, Vatansever A, Demiryürek D, Ergun M, Özsoy H. Tendon of Flexor Carpi Radialis in carpal tunnel: a radiologic and cadaveric study. Turk J Med Sci. 2021 Aug 30;51(4):1912-1916. doi: 10.3906/sag-2012-31. PMID: 33705637; PMCID: PMC8569728. Pubmed
5. .Lee YM, Song SW, Sur YJ, Ahn CY. Flexor carpi radialis brevis: an unusual anomalous muscle of the wrist. Clin Orthop Surg. 2014 Sep;6(3):361-4. doi: 10.4055/cios.2014.6.3.361. Epub 2014 Aug 5. PMID: 25177465; PMCID: PMC4143527. Pubmed