Accessory flexor carpi ulnaris muscle
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The accessory flexor carpi ulnaris muscle is considered very rare 1,2.
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
- 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
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.
On ultrasound, the accessory flexor carpi ulnaris muscle is characterized by a muscle like well-defined hypoechoic echotexture 2.
The accessory flexor carpi ulnaris muscle can be visualized 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.
It might be confused with a pathologic condition on imaging such as a soft tissue tumor 4.
The accessory flexor carpi ulnaris muscle has been implicated in the following clinical conditions 1:
- volar ulnar swelling
- ulnar nerve entrapment
- 1. Pressney I, Upadhyay B, Dewlett S, Khoo M, Fotiadou A, Saifuddin A. Accessory Flexor Carpi Ulnaris: Case Report and Review of the Literature. BJR|case Reports. 2020;6(3):20200010. doi:10.1259/bjrcr.20200010 - Pubmed
- 2. Bhardwaj P, Bhandari L, Sabapathy S. Supernumerary Flexor Carpi Ulnaris — Case Report and Review. Hand Surg. 2013;18(03):393-7. doi:10.1142/s0218810413720222 - Pubmed
- 3. Sakthivel S & Verma S. Accessory Flexor Carpi Ulnaris and Bilaterally Variant Vascular Anatomy of Upper Limb: An Unusual Presentation. Int J App Basic Med Res. 2017;7(2):143. doi:10.4103/ijabmr.ijabmr_326_16 - Pubmed
- 4. Pires L, Machado G, Fernandes R, Manaia J, Champs J, Babinski M. Notes on the Accessory Flexor Carpi Ulnaris Muscle: A Rare Supernumerary Variation. J Morphol Sci. 2019;36(02):138-40. doi:10.1055/s-0039-1681108
- 5. Çıftçıoğlu E, Kopuz C, Çorumlu U, Demır M. Accessory Muscle in the Forearm: A Clinical and Embryological Approach. Anat Cell Biol. 2011;44(2):160. doi:10.5115/acb.2011.44.2.160 - Pubmed
- 6. Anatole-Félix le Double. Traité Des Variations Du Système Musculaire De L'Homme Et De Leur Signification Au Point De Vue De L'Anthropologie Zoologique, Vol. 2 (Classic Reprint). (2016) ISBN: 9781333171803 - Google Books