Accessory flexor digitorum superficialis indicis muscle
- origin: flexor digitorum superficialis tendon near the transverse carpal ligament
- insertion: metacarpal head of the index finger near the A1 pulley
The accessory flexor digitorum superficialis muscle of the index finger is characterized by several variations that have been reported in the literature. It usually arises from the flexor digitorum superficialis tendon at the level of the transverse carpal ligament and runs through the carpal tunnel and within the flexor tendon sheath to insert near the metacarpophalangeal joint of the index finger 1-5.
Variations of the accessory flexor digitorum superficialis indicis muscle include the following 1:
- replacement of the normal tendon with a muscle belly within the palm
- digastric muscle with components in the palm and the forearm
- muscular component extending into but not through the carpal tunnel
The accessory flexor digitorum superficialis indicis muscle can be nicely visualized on an MRI of the wrist. It travels deep in the subcutaneous tissue through the carpal tunnel and the distal tendon or palmar muscle belly extends into the flexor tendon sheath 1.
History and etymology
The accessory flexor digitorum superficialis indicis muscle was first described by Donald Mainland in 1927 as ‘an uncommon abnormality of the flexor digitorum sublimis muscle'.
Depending on the variant anatomy the accessory flexor digitorum muscle of the index finger might be confused with a pathologic condition such as a tumor 1,2.
The accessory flexor digitorum muscle of the index finger has been implicated in the following clinical conditions 1,2:
- carpal tunnel syndrome
- chronic wrist pain
- wrist tumor
- 1. Sookur PA, Naraghi AM, Bleakney RR, Jalan R, Chan O, White LM. Accessory muscles: anatomy, symptoms, and radiologic evaluation. (2008) Radiographics : a review publication of the Radiological Society of North America, Inc. 28 (2): 481-99. doi:10.1148/rg.282075064 - Pubmed
- 2. Timins ME. Muscular anatomic variants of the wrist and hand: findings on MR imaging. (1999) AJR. American journal of roentgenology. 172 (5): 1397-401. doi:10.2214/ajr.172.5.10227524 - Pubmed
- 3. Javed S, Woodruff M. Carpal tunnel syndrome secondary to an accessory flexor digitorum superficialis muscle belly: case report and review of the literature. (2014) Hand (New York, N.Y.). 9 (4): 554-5. doi:10.1007/s11552-014-9622-1 - Pubmed
- 4. Park SH. Anomalous Muscles of the Wrist Encountered During Endoscopic Carpal Tunnel Surgery. (2019) Journal of Korean Neurosurgical Society. 62 (1): 90-95. doi:10.3340/jkns.2018.0111 - Pubmed
- 5. Mainland D. An Uncommon Abnormality of the Flexor Digitorum Sublimis Muscle. (1927) Journal of anatomy. 62 (Pt 1): 86-9. Pubmed