The flexor carpi ulnaris (FCU) is a muscle located in the forearm. It contributes to movement and stability of the wrist joint, enabling various hand and wrist actions.
Anatomy and Location
The flexor carpi ulnaris is located in the anterior compartment of the forearm, along the ulnar or medial side, closer to the little finger. It originates with two distinct heads: a humeral head from the medial epicondyle of the humerus, and an ulnar head from the olecranon and the upper two-thirds of the posterior border of the ulna.
These two heads are connected by a tendinous arch, and the ulnar nerve and ulnar artery pass between them as they enter the forearm. The muscle’s fibers converge into a long tendon that inserts into specific bones in the wrist and hand: the pisiform bone, the hook of the hamate bone, and the base of the fifth metacarpal bone, which is the long bone leading to the little finger. The flexor carpi ulnaris is the most medial of the superficial flexor muscles in the forearm.
Primary Actions
The flexor carpi ulnaris primarily acts at the wrist joint. It performs wrist flexion, which is bending the hand forward, bringing the palm closer to the forearm. This movement often occurs in conjunction with other wrist flexors.
The muscle also contributes to ulnar deviation, also known as wrist adduction. This action involves moving the hand sideways towards the little finger side of the forearm. It works with the extensor carpi ulnaris to produce this specific sideways motion. These combined actions are important for gripping, grasping, and stabilizing the wrist during various tasks, from typing to sports activities like swinging a golf club or tennis racket.
Nerve and Blood Supply
The flexor carpi ulnaris receives its nerve supply from the ulnar nerve. This nerve originates from the brachial plexus and transmits signals to the muscle, enabling it to contract. It is the only muscle in the anterior compartment of the forearm that is fully innervated by the ulnar nerve.
The muscle is primarily nourished by branches of the ulnar artery. Proximally, a branch of the posterior ulnar recurrent artery supplies the muscle. Branches of the ulnar artery itself supply the middle and distal parts. The ulnar artery also supplies various other muscles of the forearm and hand.
Common Issues Affecting the Muscle
The flexor carpi ulnaris and its associated structures can be affected by several conditions, often stemming from overuse or repetitive strain. One common issue is tendinitis, an inflammation of its tendon. This typically causes pain and discomfort on the underside of the wrist, particularly when flexing or rotating the wrist. Activities involving repetitive wrist movements, such as those in construction, racquet sports, or weightlifting, can stress the muscle and tendon, leading to tendinitis.
The flexor carpi ulnaris also plays a role in ulnar nerve compression, particularly at the elbow, a condition known as cubital tunnel syndrome. The ulnar nerve passes between the two heads of the flexor carpi ulnaris as it enters the forearm. Compression or irritation of the nerve in this area can lead to symptoms such as numbness and tingling in the little finger and half of the ring finger, as well as weakness in grip strength. Repetitive elbow flexion can reduce the size of the cubital tunnel, increasing pressure on the ulnar nerve and contributing to this syndrome.
Another site of potential ulnar nerve entrapment is where the nerve exits the flexor carpi ulnaris muscle. While less common, the flexor carpi ulnaris tendon can also be involved in calcific tendinitis, where calcium deposits occur at its insertion point. Overuse and repetitive motions can lead to pain and swelling.