The accessory flexor carpi ulnaris (AFCU) is a rare accessory muscle of the forearm and wrist and a normal anatomical variant that can be found in addition to a normal flexor carpi ulnaris muscle.
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Epidemiology
The accessory flexor carpi ulnaris muscle is considered very rare 1,2.
Associations
It has been associated with other muscular variants of the forearm such as 2-4:
- flexor carpi radialis brevis vel profundus
- absent palmaris longus
- duplication of the palmaris longus
- persistent median artery
Summary
- origin: medial surface of the ulna, deep and anterior to the extensor carpi ulnaris muscle belly
- insertion: pisiform bone radial to the flexor carpi ulnaris muscle insertion and/or flexor retinaculum
- innervation: variable median nerve or ulnar nerve innervation
Gross anatomy
The accessory flexor carpi ulnaris muscle is an extra muscle of the medial volar forearm with features of the normal flexor carpi ulnaris muscle and variably of the palmaris longus muscle. It originates from the medial surface of the ulna, courses radial or deep to the normal flexor carpi ulnaris muscle and inserts at the pisiform separate and radial to the insertion of the latter and variably to the flexor retinaculum 1,2.
Variant anatomy
Variant insertions of the accessory flexor carpi ulnaris include the hook of the hamate, the abductor digiti minimi or the base of the fifth metacarpal bone 5.
Radiographic features
Ultrasound
On ultrasound, the accessory flexor carpi ulnaris muscle is characterised by a muscle like well-defined hypoechoic echotexture 2.
MRI
The accessory flexor carpi ulnaris muscle can be visualised on MRI of the wrist and forearm on the ulnar side deep to flexor carpi ulnaris muscle 1.
History and etymology
According to Le Double, the accessory flexor carpi ulnaris muscle was described first by the French anatomist Jean-Francois Jarjavay in 1857 6.
Clinical importance
It might be confused with a pathologic condition on imaging such as a soft tissue tumour 4.
Related pathology
The accessory flexor carpi ulnaris muscle has been implicated in the following clinical conditions 1:
- volar ulnar swelling
- ulnar nerve entrapment
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