The flexor carpi ulnaris- named from its influence upon the wrist and its position - is a thick sheet of muscular fibre, somewhat fusiform in shape, which wraps round the convex ulnar border of the forearm.

Origin

First head :

• by the common tendon from the lower part of the front of the internal condyle ;
• the deep fascia of the forearm, and the septa which intervene between the muscle and the pahnaris longus and flexor subhmis digitorum.

The second head : from the inner surface of the olecranon process, and the upper two-thirds of the posterior border of the ulna.

Insertion

The upper surface of the pisiform bone, beyond which fibres are continued to the unciform process, and the front of the base of the fifth metacarpal bone.

Structure

The origin of the upper head is tendinous, and that of the lower is partly fleshy, partly aponeurotic ; the aponeurosis from the posterior ridge of the ulna being common to it with the flexor profundus digitorum and the extensor carpi ulnaris, and being closely blended with the deep fascia of the back of the forearm. The two heads are united by a fibrous arch under which passes the ulnar nerve. From this tendinous and bony origin the fleshy fibres pass downwards and forwards in a penniform manner to be inserted into the posterior aspect of a tendon which appears on the front of the muscle a little above the middle of the forearm, and becomes free just above the wrist joint, where it lies superficial and internal to the anterior annular ligament at its insertion into the pisiform bone.

Nerve-supply

From the inner cord of the brachial plexus (through the eighth cervical and first thoracic nerves) by filaments from the ulnar nerve which enter the deep surface of the muscle above the middle of the forearm.

Action

• Flexor of the wrist. The pisiform bone assists this action by lifting the line of the tendon a little from the metacarpal bone, much as the patella assists the quadriceps femoris.
• It assists somewhat feebly in adduction of the wrist.
• It helps in the flexion of the elbow.

Relations

Superficially, the deep fascia and superficial veins ; deeply, the flexor | profundus digitorum, the ulnar vessels and nerve. Near the wrist the ulnar artery lies along the outer border of the tendon.

Variations

Its insertion sometimes extends to the anterior annular ligament, and occasionally it sends a slip to the base of the fourth metacarpal bone.