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Flexor Carpi Ulnaris (FCU)

Key Points:
•  Flexes and adducts the wrist.
• Tendon transfers – The flexor carpi radialis (FCR) is the better wrist flexor to use compared to the flexor carpi ulnaris (FCU) in radial nerve palsy patients. FCU is stronger wrist flexor than FCR and the power wrist flexor for manual labor.
Muscle Function:
Primary: Flexes and adducts the wrist.
Secondary: May assist in flexion of the elbow.
Palpation: Distal wrist crease on the tendon in line with the fifth metacarpal just proximal to the pisiform.
Strength Testing:
Gravity-lessened Test: Position – the subject in sitting with elbow slightly flexed and forearm in neutral position. The forearm is rested on a table, wrist at the edge, and hand off the edge. Wrist is in extension. Stabilize – the forearm and wrist in extension. Support – through the full range of motion.
Anti-gravity Test: Position – the forearm in supination and the wrist in extension. Stabilize – the forearm and wrist in extension. Resist – against full flexion of the wrist with slight ulnar deviation (in the direction of wrist extension and radial deviation).
Or, place the patient’s wrist in slight ulnar deviation and wrist flexion. While the patient is holding that position, the examiner attempts to move their hand into wrist extension as the patient is resisting.
Possible Substitutions: Palmaris longus, flexor carpi radialis, extensor carpi ulnaris, muscles for finger flexion, and the abductor digiti minimi. Monitor ulnar deviation during flexion to be sure the subject is not pulling into any ulnar deviation.
Relevant Anatomy:
• Roots: C7, C8, T1.
• Nerve: Ulnar nerve.
• Innervation Route: C7, C8, T1 → ulnar nerve → flexor carpi ulnaris branch.
Origin of Humeral Head: Common flexor tendon from medial epicondyle of humerus. 
Origins of Ulnar Head: Aponeurosis from medial margin of olecranon, proximal ⅔ of posterior border of ulna and from deep antebrachial fascia.
Insertions: Pisiform bone, then by ligaments, to hamate and small finger metacarpal bones.