Flexor Carpi Ulnaris Muscle

Anatomy and Location

The flexor carpi ulnaris is part of the medial compartment of the forearm, which contains muscles originating from the medial epicondyle of the humerus. Within the first (superficial) layer of this group, it occupies the most medial position.

The muscle has two heads:

• Humeral head (caput humerale) — originates from the medial epicondyle (epicondylus medialis).
• Ulnar head (caput ulnare) — originates from the olecranon (olecranon).

Near the elbow joint, the muscle forms a tendinous arch. Distally, the tendon of the flexor carpi ulnaris runs deep to the deep fascia of the forearm (fascia propria) on the ulnar side.

Insertion (Insertio): The tendon inserts into the pisiform bone (os pisiforme). Tendinous fibers then continue to the hook of the hamate bone (hamatum) and the base of the 5th metacarpal bone.

Function

The main functions of the flexor carpi ulnaris are:

• Wrist flexion.
• Ulnar deviation (adduction) — movement of the wrist toward the ulnar side.

Blood Supply and Innervation

• Innervation: n. ulnaris (C7–C8).
• Blood supply: a. ulnaris, superior and inferior ulnar collateral arteries (a. collateralis ulnaris superior et inferior).

Topography and Relation to Neurovascular Bundles

The flexor carpi ulnaris serves as a key landmark for locating the ulnar neurovascular bundle in the forearm:

• Proximal third of the forearm: The ulnar nerve (n. ulnaris) passes between the humeral and ulnar heads of the m. flexor carpi ulnaris.
• Middle and distal thirds: The ulnar artery (a. ulnaris) runs in the groove between the flexor carpi ulnaris and the flexor digitorum superficialis (m. flexor digitorum superficialis). At the junction with the middle third, the ulnar nerve joins the artery, running medial to it.
• Wrist region: Deep to the tendon of the flexor carpi ulnaris on the medial side runs the dorsal carpal branch of the ulnar artery (ramus carpalis dorsalis), which then pierces the fascia to reach the dorsum of the hand.
• Guyon's canal (canalis ulnaris): At the lateral margin of the pisiform bone, the deep fascia splits to form a canal containing the ulnar neurovascular bundle.

Adjacent Structures on Cross-Sections

On cross-sections of the forearm, neighboring structures include the ulna (ulna), deep digital flexor (m. flexor digitorum profundus), and ulnar nerve.

In the superficial layer lateral to the flexor carpi ulnaris, the following structures are located sequentially:

1. Palmaris longus muscle (m. palmaris longus).
2. Flexor carpi radialis muscle (m. flexor carpi radialis).
3. Pronator teres muscle (m. pronator teres).

Note: In the elbow region, separating these superficial muscles can be difficult; their course is more easily distinguished distally in the anterior forearm compartment.