Flexor carpi ulnaris muscle

The flexor carpi ulnaris muscle (or FCU) is a muscle of the human forearm that acts to flex and adduct (medial deviation) the hand.

Flexor carpi ulnaris
Dorsal (left) and ventral (right) views of deep muscles of the forearm. FCU is visible in blue.
OriginMedial epicondyle (common flexor tendon) and medial margin on olecranon of ulna
InsertionPisiform, hook of the hamate, base of the fifth metacarpal bone
ArteryUlnar artery
NerveMuscular branches of ulnar nerve (from C8 and T1)
ActionsFlexion and adduction of wrist
AntagonistExtensor carpi radialis brevis muscle and extensor carpi radialis longus muscle
LatinMusculus flexor carpi ulnaris
Anatomical terms of muscle


Flexor carpi ulnaris muscle arises by two heads, humeral and ulnar, connected by a tendinous arch beneath which the ulnar nerve and artery pass.

Its insertion is into the pisiform bone, into the hamate bone by the pisohamate ligament and into the fifth metacarpal bone by the pisometacarpal ligament.

The muscle acts to flex and adduct the wrist joint.

Nerve supply

The flexor carpi ulnaris muscle is innervated by the ulnar nerve that has its roots in the C8 and T1 spinal nerves.


The tendon of flexor carpi ulnaris can be seen on the anterior of the distal forearm. On a person's distal forearm, just before the wrist, there are either two or three tendons. The tendon of the flexor carpi ulnaris is the most medial (closest to the little finger) of these. The most lateral one is the tendon of flexor carpi radialis muscle, and the middle one, not always present, is the tendon of palmaris longus.


The muscle, like all flexors of the forearm, can be strengthened by exercises that resist its flexion. A wrist roller can be used and wrist curls with dumbbells can also be performed. These exercises are used to prevent injury to the ulnar collateral ligament of elbow joint.

Clinical significance

Ulnar entrapment by the aponeurosis of the two heads of the flexor carpi ulnaris muscle may cause cubital tunnel syndrome.

Additional images

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