Long Abductor Digiti Minimi Muscle: Variation of the Hypothenar Muscles and Clinical Consequences

Abstract

Variations in the hypothenar muscles influence the susceptibility of Guyon's canal and surgical procedures in this region. The hypothenar regions of both hands of 38 human donors were dissected and the single muscles identified. A semiquantitative evaluation included 19 donors. The opponens digiti minimi and the abductor digiti minimi were constantly present. The flexor digiti minimi showed various appearances: in 58% it formed one belly, in 21% two bellies, and in 21% it was missing. Rare unilateral supernumerary muscles (2.5% in this study) were associated to the abductor digiti minimi. The variation of the flexor digiti minimi and the possible appearance of additional muscles should be recognized for hypothenar region pathologies. Clin. Anat., 33:643–645, 2020. © 2019 Wiley Periodicals, Inc.

Aberrant accessory abductor digiti minimi manus muscle: a rare anatomical variation

“…The existence of an AADM muscle has been previously described and C.A. May recently proposed the use of term "long abductor digiti minimi" for this category of aberrant muscles [16]. However, we describe a unique case of an AADM that originates from the tendons of the flexor digitorum superficialis and insert to the head of the 5 th metacarpal.…”

“…The radial, middle, and ulnar blastemas are responsible for the development of the abductor pollicis brevis, flexor digitorum superficialis, and abductor digiti minimi muscles (in that order) [17]. Thus, the flexor digitorum superficialis originates in the carpal area, but its blastema migrates proximally [18], and the abductor digiti minimi and abductor pollicis brevis originate from where their blastema started [16].…”

“…Generally, the existence of an AADM muscle has been implicated with ulnar nerve compression at the wrist [7,16]. Dimitriou (2007) reported a case of intraoperative identification of an AADM that was covering Guyon's canal and creating apparent undue pressure on the ulnar nerve proximal to its bifurcation [20].…”

Before assessing a novel muscle in the hand, please be very careful

“…I would like to point out that when the authors pretend to describe something unique nowadays, they need to present it in clear and informative dissection, excellent photographs and no misdescriptions in the text. 5) In the discussion the authors state that the existence of an accessory AADM muscle has been previously described [4]. According to this consideration and to the description in the case report section, Antonopoulos et al [1] accept the described unique muscle as a hypothenar variation; this is in contrast to their previous assessment for an extra wrist muscle in the abstract.…”