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Flexor Carpi Ulnaris Muscle Anatomy

The flexor carpi ulnaris (FCU) muscle is the most medial of the superficial flexor muscles located in the anterior compartment of the forearm.

Flexor Carpi Ulnaris Muscle Anatomy

The flexor carpi ulnaris muscle originates from 2 separate heads connected by a tendinous arch. The humeral head arises from a common flexor tendon origin on the medial humeral epicondyle. In contrast, the ulnar head arises by an aponeurosis from the olecranon and proximal three-fourths of the ulna’s subcutaneous margin.

The flexor carpi ulnaris muscle inserts on the 5th metacarpal, hook of the hamate, and pisiform. The muscle is attached to the hook of the hamate via the pisohamate ligament and the 5th metacarpal bone through the pisometacarpal ligament.

The FCU simultaneously flexes and adducts the hand at the wrist if acting alone. It flexes the wrist when it acts with the FCR and adducts it when acting with the extensor carpi ulnaris.

The ulnar nerve enters the forearm by passing between the humeral and ulnar heads of its proximal attachment. This muscle is exceptional among muscles of the anterior compartment, being fully innervated by the ulnar nerve. The tendon of the flexor carpi ulnaris is a guide to the ulnar nerve and artery, which are on its lateral side at the wrist.

See Also: Forearm Muscles Anatomy & Function
OriginHumeral head: medial epicondyle of humerus.
Ulnar head: olecranon and posterior border of ulna
InsertionPisiform bone
Hook of hamate bone
5th metacarpal bone
InnervationUlnar nerve (C7 and C8) (C7, C8)
Blood SupplyUlnar artery
ActionFlexes and adducts hand (at wrist)
Flexor carpi ulnaris origin and insertion
Flexor carpi ulnaris origin and insertion

To test the flexor carpi ulnaris, the person puts the posterior aspect of the forearm and hand on a flat table and is then asked to flex the wrist against resistance while the examiner palpates the muscle and its tendon.

flexor carpi ulnaris tendinopathy is an overuse injury presenting with focal volar and ulnar-sided wrist pain. The pain may be reproduced by wrist flexion and ulnar deviation. The pisiform is a sesamoid within the FCU tendon contributing to tendonitis-related wrist pain

References & More

  1. Clinically Oriented Anatomy – 8th Edition
  2. Lung BE, Siwiec RM. Anatomy, Shoulder and Upper Limb, Forearm Flexor Carpi Ulnaris Muscle. [Updated 2024 Jan 30]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: Pubmed
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