Novel, bilateral, two-bellied muscles span the extensor forearm, thenar eminence to insert on the proximal phalanx of the thumb: Clinical and embryological significance

P. L. Mishall, A. N. Marsh, D. Perez, X. H. Quezada, M. C. Stahl, R. E. Weinstock, S. A. Downie

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

Muscle and tendon variations in the forearm, wrist and hand are commonly reported in the anatomical and surgical literature. They are frequently the source of inflammatory conditions such as de Quervain’s tenosynovitis or carpal tunnel syndrome. During academic dissection, a cadaver presented with bilateral, additional muscles running parallel to the abductor pollicis longus muscles (APL) in the extensor compartment of the forearm. Both additional muscles had two bellies, one proximal and one distal, with an intervening tendon. The proximal bellies were separate and distinct from the adjacent APLs. The tendons traversed the first dorsal compartments with the tendons of the APLs and the extensor pollicis brevis muscles (EPB). The distal bellies lay adjacent to the abductor pollicis brevis (APB) muscles in the thenar compartments, and inserted onto the volar base of the proximal phalanges of the thumbs. Following a thorough search of the literature, we determined that these additional muscles constitute a previously unreported variation. This report details the variation, compares it with other reported variations, presents the related embryology, and reviews the significance of this variation as it relates to inflammatory conditions and surgical procedures.

Original languageEnglish (US)
Pages (from-to)182-187
Number of pages6
JournalFolia Morphologica
Volume79
Issue number1
DOIs
StatePublished - Mar 3 2020

Keywords

  • De Quervain’s syndrome
  • Extensor compartment forearm
  • Novel muscles

ASJC Scopus subject areas

  • Anatomy
  • Histology

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