Flexor carpi radialis muscle

Origin and insertion

Flexor carpi radialis originates from the medial epicondyle of humerus, via the common flexor tendon, and surrounding fascia (antebrachial fascia and intermuscular septa). This common flexor tendon is a common origin for the six long flexor muscles in the forearm; flexor carpi radialis, palmaris longus, flexor carpi ulnaris, pronator teres, flexor digitorum superficialis and profundus. 

From the medial epicondyle, the muscle belly courses obliquely, crossing from the ulnar to the radial part of the forearm. In the lower third of the forearm, it gives off a long tendon that passes below the flexor retinaculum into the palmar surface of the hand. Within the flexor retinacular space, the tendon passes through its own synovial sheath. It then crosses the palmar surface of the scaphoid bone and traverses in a groove on the surface of the trapezium bone. The tendon then inserts to the palmar surface of the bases of metacarpal bones 2-3.

Relations

Flexor carpi radialis lies deep to the forearm skin and superficial to the flexor digitorum superficialis muscle. It is lateral to palmaris longus, while being medial to pronator teres in its proximal part and to brachioradialis in its distal part. In the hand, the attaching tendinous fibers lie deep to the oblique head of adductor pollicis muscle.

In relation to neurovascular structures, the proximal part of the muscle covers the median nerve, prior to it passing beneath the flexor digitorum superficialis muscle. Just proximally to the wrist, the radial artery runs between the tendons of flexor carpi radialis and brachioradialis muscles, marking a common site for its palpation in order to measure someone’s radial pulse. 

Innervation

Innervation to flexor carpi radialis comes from the medial and lateral cords of the brachial plexus via the median nerve (C6, C7).

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Blood supply

Flexor carpi radialis is mostly supplied by a branch arising high in the forearm from the anterior or posterior recurrent ulnar arteries. The rest of its nutritional needs are fulfilled by 6-8 branches of the radial artery.

Function

Due to its oblique course, flexor carpi radialis pulls the hand proximally and laterally, meaning that it is able to produce the combined motion of wrist flexion and wrist abduction (radial deviation). Acting together with flexor carpi ulnaris and palmaris longus, it produces a balanced flexion of hand, i.e. flexion without abduction. However, when it works in synergy with extensor carpi radialis longus and brevis, the net result of their counteracting forces is a balanced hand abduction. 

To a lesser extent, the muscle contributes to pronation as it obliquely crosses the forearm. It is also active during extension of the digits, preventing unwanted extension of the hand.

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