Flexor carpi radialis brevis vel profundus

The flexor carpi radialis brevis (FCRB) vel profundus muscle is an accessory muscle of the forearm and wrist and a normal anatomical variant.

Epidemiology

The flexor carpi radialis brevis vel profundus muscle has been found in 2-8% of anatomical dissections ^1-3.

Summary

• origin: anterior surface of the lower third of the distal radius
• insertion: second to fourth metacarpal base and the capitate or other radial sided carpal bones
• innervation: anterior interosseous nerve

Gross anatomy

The flexor carpi radialis brevis vel profundus muscle originates from the volar radial surface distal and radial to the flexor pollicis longus and runs deep to the flexor carpi radialis muscle ^1-4. It might show several variant accessory fibers from other anatomical structures of the forearm ¹. It traverses the pronator quadratus superficially and runs deep to the flexor retinaculum through the osteofibrous tunnel of the flexor carpi radialis and inserts to the radial carpus and to the bases of the second to fourth metacarpophalangeal joints ^1-4.

Variant anatomy

The flexor carpi radialis brevis vel profundus can have accessory fibers from various sources and might appear as bi capitate muscle including ¹:

• pronator teres muscle
• antebrachial aponeurosis
• flexor pollicis longus muscle
• interosseous membrane
• the anterior surface of the ulna
• distal humerus

Variations in tendon insertion include several radial-sided carpal bones ¹.

Radiographic features

MRI

The flexor carpi radialis brevis vel profundus muscle can be nicely visualized on MRI of the wrist on the radial side deep to flexor carpi radialis and flexor pollicis longus tendons and superficial to the radial insertion of the pronator quadratus muscle ⁴.

History and etymology

The muscle was first described by the French M. Fano in 1851 under the name ‘Radiocarpien’. The name flexor carpi radialis brevis vel profundus was given to the muscle by the British surgeon, anatomist and physiologist John Wood in 1867 ^1,2,5. The French physician and anatomist Anatole-Félix le Double described several cases of the muscle in 1897 and called it ‘Court Radial anterieur’ ⁶.

Clinical importance

Surgeons might come across the flexor carpi radialis brevis vel profundus muscle during volar plate fixation of the distal radius ^2,3. It might be confused with a pathologic condition on imaging such as a tumor ⁴.

Related pathology

The flexor carpi radialis brevis vel profundus muscle has been implicated in the following clinical conditions ^2-4:

• volar wrist pain and tenosynovitis
• volar radial mass
• carpal tunnel syndrome