Flexor carpi ulnaris muscle

Origin and insertion

Flexor carpi ulnaris originates with two heads which are linked by a tendinous arch. The heads are named according to the bones they attach to;

• The smaller humeral head arises from the common flexor origin on the medial epicondyle of humerus.
• The more extensive ulnar head originates from the olecranon and proximal part of the posterior border of ulna. 

As the muscle fibers pass towards the wrist joint, they converge on a long tendon in the distal part of the forearm. This tendon passes into the palmar surface of the hand to insert onto the pisiform and hamate carpal bones, as well as onto the base of the fifth metacarpal bone.

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Relations

The tendon of flexor carpi ulnaris can be seen and palpated beneath the skin immediately proximal to the wrist joint. It is the most medial of the tendons that are visible superficially in this region.

Flexor carpi ulnaris lies superficial to flexor digitorum superficialis and medial to palmaris longus. As they pass into the forearm, the ulnar nerve and posterior ulnar recurrent artery pass deep to the tendinous arch between the humeral and ulnar heads of the muscle. Distally, the ulnar artery and ulnar nerve lie lateral to the tendon of flexor carpi ulnaris.

Innervation

Innervation of the flexor carpi ulnaris muscle is from the brachial plexus via the ulnar nerve (C7-T1).

Blood supply

Flexor carpi ulnaris receives its arterial blood supply via three different routes. Proximally, a branch of the posterior ulnar recurrent artery supplies the muscle as it passes between the humeral and ulnar heads. Branches of the ulnar artery supply the middle and distal parts of the muscle, with an accessory supply also present distally via the inferior ulnar collateral artery.

Function

Due to its position and direction in the forearm, flexor carpi ulnaris can move the hand sideways as well as flexing it. Contracting with flexor carpi radialis and palmaris longus, flexor carpi ulnaris produces flexion of the hand at the wrist joint.

However, when it contracts alongside the extensor carpi ulnaris muscle in the posterior compartment, their counteracting forces produce adduction of the hand at the wrist, otherwise known as ulnar deviation or ulnar flexion.