Flexor Carpi Ulnaris Muscle Anatomy

Location & Overview

The flexor carpi ulnaris muscle is the most powerful wrist flexor. It has two heads, a humeral head and a ulnar head, which are linked by a tendinous arch. It is located in the anterior compartment of the forearm. It is one of the superficial flexor muscles of the forearm and the most medial of these superficial flexor muscles. The other superficial forearm flexors are the palmaris longus, pronator teres, flexor carpi radialis, and the flexor digitorum superficialis.^[1]

The flexor carpi ulnaris muscle plays an important role in various activities. For instance, it is helpful in weightlifting exercises that involve wrist flexion and adduction. In racquet sports such as tennis or badminton, the flexor carpi ulnaris stabilizes the wrist during hitting and provides the required force for wrist flexion and adduction during the swing. Similarly, in golf, it assists with generating the necessary force for wrist flexion and adduction during the swing, particularly in the follow-through. The flexor carpi ulnaris muscle also assists in everyday activities such as typing, writing by hand, and DIY home improvements by aiding in stabilizing and holding tools like hammers and saws.

Origin & Insertion

The flexor carpi ulnaris muscle has two heads: a humeral head and a ulnar head. The humeral head originates from the medial epicondyle of the humerus via the common flexor tendon. The ulnar head originates from the olecranon and the proximal part of the posterior border of the ulna. These two heads are connected proximally by a tendinous arch, and the ulnar nerve passes between them as it enters the forearm.^[2,3]

The muscle continues down the medial side of the forearm and forms a tendon near the wrist. This tendon attaches to the pisiform bone. From the pisiform, its attachment is continued to the hook of the hamate via the pisohamate ligament and to the base of the fifth metacarpal bone via the pisometacarpal ligament. For this reason, the pisiform, hook of hamate, and base of the fifth metacarpal are commonly listed as insertion sites of the flexor carpi ulnaris, even though the hamate and fifth metacarpal attachments are reached through ligamentous continuations from the pisiform.^[2,3,4]

Action & Function

The flexor carpi ulnaris is a powerful flexor of the wrist and also adducts the hand at the wrist joint. Wrist adduction is also called ulnar deviation, because the hand moves toward the ulnar side of the forearm. When flexor carpi ulnaris works with flexor carpi radialis, the two muscles help produce balanced wrist flexion. When flexor carpi ulnaris works with extensor carpi ulnaris, the two muscles help produce balanced wrist adduction.^[5,3]

The flexor carpi ulnaris may also assist weakly with elbow or forearm flexion because it crosses the elbow region proximally, but this is not one of its main actions. Its main functional role is at the wrist, where it contributes to wrist flexion, wrist adduction, and medial-side wrist stability. Its attachment to the pisiform also helps stabilize the pisiform, giving abductor digiti minimi a stable origin during movement of the little finger.^[2,3]

Innervation

The flexor carpi ulnaris is innervated by muscular branches of the ulnar nerve. The ulnar nerve passes behind the medial epicondyle, travels through the cubital tunnel, and then enters the forearm between the two heads of the flexor carpi ulnaris. This close relationship is clinically important because the nerve passes through a narrow region at the medial side of the elbow before continuing down the forearm.^[3,2]

The spinal nerve root contribution to the flexor carpi ulnaris is commonly listed as C7 and C8, although T1 is also included in some anatomical descriptions of the ulnar nerve supply. This variation reflects how fibers from the brachial plexus contribute to the ulnar nerve. Cadaveric and electrophysiological research also supports an important C7 contribution to the flexor carpi ulnaris, which helps explain why this muscle may be relevant when assessing some cervical nerve-root or brachial plexus problems.^[5,3,6]

Blood Supply

Blood is supplied to the flexor carpi ulnaris mainly by branches of the ulnar artery and the posterior ulnar recurrent artery. The posterior ulnar recurrent artery passes deep to the flexor carpi ulnaris and ascends between its two heads with the ulnar nerve. This artery supplies the flexor carpi ulnaris, neighboring forearm flexor muscles, the ulnar nerve, nearby bone, and the elbow joint.^[3,2]

The arterial supply is usually described in terms of vascular pedicles, which are small vessel bundles that enter the muscle. A proximal pedicle arises from the posterior ulnar recurrent artery as it passes between the humeral and ulnar heads of the muscle. Additional middle and distal pedicles arise from the ulnar artery, with the distal pedicle entering near the musculotendinous junction. A smaller contribution near the origin may also come from the inferior ulnar collateral artery.^[3]

Cadaveric studies show that this vascular pattern can vary. One anatomical study found that the ulnar artery supplied the dominant vascular pedicle in 86% of cases, while the posterior ulnar recurrent artery supplied the dominant pedicle in 14% of cases. The same study described several additional smaller vessels supplying the muscle and noted that the motor nerve entry point is close to the main vascular pedicles. Another cadaveric study found vascular pedicles from the ulnar artery or recurrent ulnar artery in 24 of 25 specimens, with the first pedicle located an average of 5.7 cm from the medial epicondyle.^[7,8]