Flexor Carpi Ulnaris

The flexor carpi ulnaris is a superficial muscle in the anterior compartment of the forearm. It plays a key role in flexing and adducting the wrist. It is the most medial of the superficial forearm flexors and forms the ulnar border of the forearm.

Location

The flexor carpi ulnaris is located on the anteromedial aspect of the forearm. It runs from the medial epicondyle of the humerus and the ulna down to the pisiform bone and the base of the 5th metacarpal.

Structure

The muscle has two heads — humeral and ulnar — and a single tendon that inserts onto the carpal bones.

• Origin:
  • Humeral head: Medial epicondyle of the humerus (via the common flexor tendon)
  • Ulnar head: Olecranon and posterior border of the ulna
• Insertion: Pisiform bone, hook of the hamate, and base of the fifth metacarpal via the pisohamate and pisometacarpal ligaments.
• Fiber Orientation: Longitudinal, converging into a strong tendon near the wrist.

Function

The flexor carpi ulnaris contributes to:

• Wrist Flexion: Works with the flexor carpi radialis to flex the wrist.
• Wrist Adduction (Ulnar Deviation): Acts with the extensor carpi ulnaris to adduct the wrist.
• Stabilization: Helps stabilize the wrist during grip or forceful hand movements.

Innervation

The muscle is innervated by the ulnar nerve (C7, C8, T1). It is the only superficial forearm flexor not innervated by the median nerve.

Blood Supply

• Ulnar artery: Primary blood supply.
• Posterior ulnar recurrent artery: May contribute proximally.

Relations

The flexor carpi ulnaris lies superficial to the flexor digitorum superficialis and overlies the ulnar artery and ulnar nerve in the distal forearm.

Surface Anatomy

The tendon of the flexor carpi ulnaris is visible and palpable on the medial side of the wrist, just anterior to the ulnar head. It serves as an important anatomical landmark for locating the ulnar nerve and artery.

Development

The muscle originates from the mesoderm of the paraxial somites during embryological limb bud development. Its innervation by the ulnar nerve reflects its medial derivation within the forearm flexor mass.

Anatomical Variations

• May have an accessory slip to the pisiform or flexor retinaculum.
• Rarely, it may be fused with adjacent muscles like the palmaris longus or flexor digitorum superficialis.

Clinical Significance

• Ulnar Nerve Compression: The ulnar nerve passes deep to the flexor carpi ulnaris at the elbow, within the cubital tunnel. Hypertrophy or entrapment can lead to cubital tunnel syndrome.
• Tendonitis: Overuse or repetitive stress can result in inflammation of the tendon, especially in athletes or manual laborers.
• Landmark for Procedures: The tendon is used as a guide during vascular access or nerve block procedures at the wrist.

Comparative Anatomy

In some non-human primates, the flexor carpi ulnaris has a more prominent role in wrist flexion due to their arboreal locomotion. In humans, its function is less dominant but still important in precision tasks and grip stabilization.