Batuhan Erhan Aktaş; Berkay Yalçınkaya; Ahmet Furkan Çolak; Murat Kara; Levent Özçakar

doi:10.12701/jyms.2025.42.50

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Image vignette Radiology, Radiotherapy & Diagnostic Imaging
Accessory abductor digiti minimi muscle detected during hand/wrist ultrasonography: Batuhan Erhan Aktaş¹, Berkay Yalçınkaya², Ahmet Furkan Çolak², Murat Kara², Levent Özçakar²; Journal of Yeungnam Medical Science 2025;42:50.
DOI: https://doi.org/10.12701/jyms.2025.42.50
Published online: August 29, 2025

¹Department of Sports Medicine, Hacettepe University Medical School, Ankara, Türkiye

²Department of Physical and Rehabilitation Medicine, Hacettepe University Medical School, Ankara, Türkiye

Corresponding author: Batuhan Erhan Aktaş, MD Department of Sports Medicine, Hacettepe University Medical School, Zemin Kat, Spor Hekimliği AD, Sıhhiye Ankara 06230, Türkiye Tel: +90-3123951347 • E-mail: batuhanerhanaktas@gmail.com

• Received: July 25, 2025 • Revised: August 12, 2025 • Accepted: August 26, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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In this illustrative figure (Fig. 1) and video (Supplementary Video 1), we wish to provide a side note for those who may be less familiar with anatomical variants encountered during musculoskeletal ultrasound. The video and figure of the accessory abductor digiti minimi (AADM) muscle were incidentally captured while practicing hand ultrasound. Accessory/aberrant muscles of the upper extremity have been previously identified and reported in the literature [1]. They are often detected incidentally during imaging, surgery, autopsy, or cadaveric dissection [2]. Although generally being of minor clinical importance, they can cause musculoskeletal complaints in some patients.

The AADM muscle is one of these variants, the most common variant in the hand and wrist, with an incidence ranging from 22% to 35% [3]. It typically originates from the antebrachial fascia or the tendons of the palmaris longus or flexor carpi radialis muscles. The most common insertion is the base of the proximal phalanx of the fifth finger [3]. It can cause ulnar nerve compression, particularly the palmar ulnar cutaneous nerve which is a distal branch of the ulnar nerve that arises from the main trunk about 5 to 10 cm proximal to the wrist crease. It passes into Guyon’s canal after piercing the palmar carpal ligament, then travels between the palmaris longus and flexor carpi ulnaris tendons [4]. In some instances, it forms connections with the superficial and deep branches of the ulnar nerve, as well as with the palmar cutaneous branch of the median nerve. This nerve can become entrapped in the presence of an AADM muscle. This accessory muscle can also mimic soft tissue swelling and be used as a graft in repair surgeries [5]. Therefore, awareness of the AADM muscle is essential to avoid misdiagnoses and unnecessary examinations or interventions.

In our case, the muscle originated from the antebrachial fascia on the ulnar side at the distal third of the right forearm and, together with the abductor digiti minimi muscle, inserted at the base of the fifth finger’s proximal phalanx (Fig. 1). Throughout its course, it was imaged with a 5- to 12-MHz linear probe (Logiq P5, GE Healthcare, Milwaukee, WI, USA) as a muscle that did not transition into a tendinous structure (Supplementary Video 1). This was compatible with the type II variant of the AADM muscle [6]. During the nerve conduction study, electrical stimulation was applied to the ulnar nerve at the elbow level, and a compound muscle action potential response was obtained from the belly of the AADM muscle. This finding confirmed that the AADM muscle was innervated by the ulnar nerve, whereby motor unit action potentials were observed during flexion/abduction of the fifth metacarpophalangeal joint. Ultrasound can detect such anatomical variations even in asymptomatic cases, like ours, thereby informing both the physician and patient of potential issues, as noted in the literature [7]. Moreover, owing to its patient-friendly nature, ultrasound does not require surgical dissection to identify variations, making it a valuable imaging tool that complements physical examination.

Supplementary materials

Supplementary Video 1 can be found at https://doi.org/10.12701/jyms.2025.42.50.

Supplementary Video 1.

Dynamic ultrasound imaging (short-axis view, from proximal to distal) depicts the accessory abductor digiti minimi muscle (stars), median nerve (thin arrow), ulnar artery (arrowhead), and nerve (thick arrow). ADM, abductor digiti minimi muscle; FDS, flexor digitorum superficialis muscle; FDP, flexor digitorum profundus muscle; P, pisiform; PQ, pronator quadratus muscle.

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Ethics statement

Informed consent was obtained from the patient.

Conflicts of interest

No potential conflict of interest relevant to this article was reported.

Funding

None.

Author contributions

Conceptualization: all authors; Data curation: BEA, BY, AFC, LÖ; Formal analysis, Supervision: BY; Investigation: BEA, MK, LÖ; Methodology: BEA, LÖ; Project administration, Resources: MK, LÖ; Software: LÖ; Visualization: BEA, BY, MK, LÖ; Writing-original draft: BEA, MK, LÖ; Writing-review & editing: BEA.

Fig. 1.

Illustration shows ultrasonographic images of the accessory abductor digiti minimi muscle (star), ulnar nerve (arrow), ulnar artery (arrowhead) in short- and long-axis views. ADM, abductor digiti minimi muscle; FDS, flexor digitorum superficialis muscle; FDP, flexor digitorum profundus muscle; MC5, fifth metacarpal; P, pisiform; PQ, pronator quadratus muscle. The blank-colored boxes represent the relevant probe positions.

References

1. Ata AM, Kara M, Aydin G, Kaymak B, Gürçay E, Özçakar L. Ultrasound imaging for muscle variations: digastric flexor carpi ulnaris, gastrocnemius tertius, and supernumerary fibularis longus in an asymptomatic family. Am J Phys Med Rehabil 2018;97:e107–9.Article PubMed
2. Borthakur D, Ganapathy A, Ansari MA, Sehgal R. Accessory flexor carpi ulnaris muscle in humans: a rare anatomical case with clinical considerations. Prague Med Rep 2024;125:163–71.Article PubMed
3. Antonopoulos I, Tsikouris G, Chrysikos D, Asouhidou I, Paraskevas G, Troupis T. Aberrant accessory abductor digiti minimi manus muscle: a rare anatomical variation. Folia Morphol (Warsz) 2024;83:221–5.Article PubMed
4. Chang KV, Wu WT, Tsai YY. Guyon canal unveiled. In: Chang KV, editor. Ultrasonography of musculoskeletal pain: insights into the upper extremity. Singapore: Springer; 2025. p. 281–301.Article
5. Wu WT, Chang KV, Hsu YC, Tsai YY, Mezian K, Ricci V, et al. Ultrasound imaging and guidance for distal peripheral nerve pathologies at the wrist/hand. Diagnostics (Basel) 2023;13:1928.Article PubMed PMC
6. Rixey A, Wenger D, Baffour F, Kakar S, McKenzie G. Accessory abductor digiti minimi muscle, less muscular than thought: an update on prevalence, morphology, and review of the literature. Skeletal Radiol 2021;50:1687–95.Article PubMed PDF
7. James MR, Rowley DI, Norris SH. Ulnar nerve compression by an accessory abductor digiti minimi muscle presenting following injury. Injury 1987;18:66–7.Article PubMed

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Figure

Accessory abductor digiti minimi muscle detected during hand/wrist ultrasonography

Fig. 1. Illustration shows ultrasonographic images of the accessory abductor digiti minimi muscle (star), ulnar nerve (arrow), ulnar artery (arrowhead) in short- and long-axis views. ADM, abductor digiti minimi muscle; FDS, flexor digitorum superficialis muscle; FDP, flexor digitorum profundus muscle; MC5, fifth metacarpal; P, pisiform; PQ, pronator quadratus muscle. The blank-colored boxes represent the relevant probe positions.

Fig. 1.

Accessory abductor digiti minimi muscle detected during hand/wrist ultrasonography