Flexor Carpi Ulnaris

Clinical Notes

• FCU is the only common flexor origin muscle innervated by the ulnar nerve — all others receive median nerve supply. This is clinically useful: if FCU is weak (poor ulnar deviation) but the other common flexor muscles are intact, the lesion is in the ulnar nerve. If all common flexor muscles are weak, the lesion is more proximal (brachial plexus) or involves both nerves.
• The ulnar nerve passes between the two heads of FCU at the cubital tunnel — this is the most common site of ulnar nerve entrapment (conditions/cubital-tunnel-syndrome).

• Cubital tunnel syndrome (conditions/cubital-tunnel-syndrome) — the ulnar nerve is compressed between the humeral and ulnar heads of FCU just distal to the medial epicondyle. This is the second most common peripheral nerve entrapment after carpal tunnel syndrome. Sustained elbow flexion tightens the two heads and compresses the nerve.
• Contributes to conditions/medial-epicondylitis — part of the common flexor origin, stressed by repetitive gripping and wrist flexion.
• Guyon's canal syndrome — the ulnar nerve and artery pass through Guyon's canal between the pisiform (FCU insertion) and the hook of hamate. FCU tightness can indirectly affect this space.

• In clients with medial elbow pain or ulnar-sided wrist complaints, FCU is typically hypertonic along its full length. Tenderness at the medial epicondyle origin overlaps with the other common flexor muscles.
• In clients with cubital tunnel symptoms (numbness in the ring and little fingers), the tissue between the two heads of FCU at the elbow is often tender and thickened. Palpation here may reproduce or exacerbate the client's tingling.
• Desk workers who rest the medial elbow on the desk surface while typing directly compress the cubital tunnel — these clients often have both FCU hypertonicity and ulnar nerve irritability.

• Responds well to longitudinal stripping along the ulnar border of the forearm. The muscle is superficial and tolerates direct techniques.
• When treating cubital tunnel symptoms, gentle release of the fascial arch between the two heads can reduce nerve compression. Use light sustained pressure — do not aggressively compress the cubital tunnel.
• Post-treatment, clients with cubital tunnel involvement often report decreased tingling in the ring and little fingers.

• The ulnar nerve passes between the two heads at the elbow — avoid sustained deep compression directly over the cubital tunnel. Pressure here can worsen ulnar nerve symptoms.
• The ulnar artery runs alongside FCU in the forearm and enters Guyon's canal at the wrist. The ulnar pulse is palpable lateral to the FCU tendon at the pisiform level.
• Do not apply aggressive friction at the pisiform insertion — the pisotriquetral joint can be irritated, and the ulnar nerve and artery pass just lateral to the pisiform.

• In any client presenting with ring and little finger numbness, check three sites in sequence: (1) the cubital tunnel between the two FCU heads (most common), (2) Guyon's canal at the pisiform/hook of hamate, and (3) the C8–T1 nerve roots (cervical spine). The cubital tunnel is by far the most common site — and direct palpation of the FCU arch over the ulnar nerve is both the diagnostic test and the treatment target.