open access

Vol 82, No 2 (2023)
Case report
Submitted: 2022-03-03
Accepted: 2022-03-23
Published online: 2022-04-05
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A unique bilateral accessory forearm flexor muscle

R. K. Fernandez1, S. Ramakrishnan1, T. T. Sukumaran1, N. Kilarkaje2, M. Pillay1
·
Pubmed: 35411546
·
Folia Morphol 2023;82(2):407-411.
Affiliations
  1. Department of Anatomy, Amrita School of Medicine, Amrita Institute of Medical Sciences, Amrita Vishwa Vidyapeetham, Kochi, Kerala, India
  2. Department of Anatomy, Faculty of Medicine, Kuwait University, Kuwait

open access

Vol 82, No 2 (2023)
CASE REPORTS
Submitted: 2022-03-03
Accepted: 2022-03-23
Published online: 2022-04-05

Abstract

Muscular and neurovascular variations in the upper extremity are of utmost clinical significance. Here we report a unique bilateral accessory muscle in the forearm and palm of an 89-year-old male cadaver. The accessory muscle presented two bellies on the right side, one in the forearm, innervated by the anterior interosseous nerve, and the other in the palm, innervated by a branch of the median nerve. A long tendon interconnected the two bellies. On the left side, the muscle had a single belly in the palm, which began at the end of a long tendon that extended from the forearm. However, on both sides, the muscle originated from the posterior surface of the flexor digitorum superficialis belly and inserted along with the first lumbrical muscle into the dorsal digital expansion of the index finger. The proximal parts of the variant muscles were sandwiched between the flexor digitorum muscles. The palmar bellies coursed distally through the carpal canal and lay deep to the superficial palmar arch, and superficial to the first lumbrical, between the thenar muscles and the lateral-most tendon of the flexor digitorum superficialis. Arguably, the accessory muscle might be a variant of a lumbrical muscle, as reported before, but innervation of the proximal belly by the anterior interosseous nerve suggests that the muscle may well be a deep accessory muscle at the forearm, probably appeared as a diverted part of the flexor digitorum profundus. Its space-occupying course through the forearm and palm, especially through the carpal canal, might be clinically significant as it might contribute to nerve compression pathologies in the upper extremity. This accessory muscle also indicates the complex nature of individual muscle formation and evolution of the upper extremity with constant changes in the morphology of muscles based on their changing functions.

Abstract

Muscular and neurovascular variations in the upper extremity are of utmost clinical significance. Here we report a unique bilateral accessory muscle in the forearm and palm of an 89-year-old male cadaver. The accessory muscle presented two bellies on the right side, one in the forearm, innervated by the anterior interosseous nerve, and the other in the palm, innervated by a branch of the median nerve. A long tendon interconnected the two bellies. On the left side, the muscle had a single belly in the palm, which began at the end of a long tendon that extended from the forearm. However, on both sides, the muscle originated from the posterior surface of the flexor digitorum superficialis belly and inserted along with the first lumbrical muscle into the dorsal digital expansion of the index finger. The proximal parts of the variant muscles were sandwiched between the flexor digitorum muscles. The palmar bellies coursed distally through the carpal canal and lay deep to the superficial palmar arch, and superficial to the first lumbrical, between the thenar muscles and the lateral-most tendon of the flexor digitorum superficialis. Arguably, the accessory muscle might be a variant of a lumbrical muscle, as reported before, but innervation of the proximal belly by the anterior interosseous nerve suggests that the muscle may well be a deep accessory muscle at the forearm, probably appeared as a diverted part of the flexor digitorum profundus. Its space-occupying course through the forearm and palm, especially through the carpal canal, might be clinically significant as it might contribute to nerve compression pathologies in the upper extremity. This accessory muscle also indicates the complex nature of individual muscle formation and evolution of the upper extremity with constant changes in the morphology of muscles based on their changing functions.

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Keywords

anatomical variations, accessory muscle, first lumbrical muscle, forearm, flexor digitorum superficialis muscle, median nerve

About this article
Title

A unique bilateral accessory forearm flexor muscle

Journal

Folia Morphologica

Issue

Vol 82, No 2 (2023)

Article type

Case report

Pages

407-411

Published online

2022-04-05

Page views

2524

Article views/downloads

828

DOI

10.5603/FM.a2022.0037

Pubmed

35411546

Bibliographic record

Folia Morphol 2023;82(2):407-411.

Keywords

anatomical variations
accessory muscle
first lumbrical muscle
forearm
flexor digitorum superficialis muscle
median nerve

Authors

R. K. Fernandez
S. Ramakrishnan
T. T. Sukumaran
N. Kilarkaje
M. Pillay

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