Association between digit ratio (2D:4D) and palmaris longus muscle agenesis according to gender: a radiological study

Year 2025, Volume: 19 Issue: 3, 93 - 100, 15.01.2026

Seda Sertel Meyvacı , Beyza Çelik , Ayşenur Buz Yaşar , Handan Ankaralı

Abstract

Objectives: The palmaris longus (PLM) muscle is a superficial forearm muscle that may be congenitally absent, with prevalence varying among populations. This study aimed to investigate the association between PLM agenesis, sex, and the digit ratio (2D:4D) using radiological imaging methods.
Methods: Wrist magnetic resonance imaging (MRI) examinations of 264 individuals (115 males and 149 females) performed at Bolu Abant İzzet Baysal University, Faculty of Medicine, Department of Radiology between 2020 and 2024 were evaluated retrospectively to assess the presence or absence of the PLM. The 2D:4D digit ratio was assessed using hand radiographs. Descriptive statistics were calculated. An independent samples t-test and Pearson’s chi-square test were applied, with the significance level set at p≤0.05.
Results: PLM was present in 83.7% and absent in 16.3% of cases. PLM was absent in 13.9% of males and 18.1% of females, with no statistically significant sex difference (p=0.359). Right and left sided absence rates were 17.4% and 15.0%, respectively, showing no significant side-related difference (p=0.605). PLM was absent in 16.1% of individuals with a 2D>4D ratio and in 16.5% of those with a 4D>2D ratio (p=0.928). No significant association was found between PLM presence and the 2D:4D ratio.
Conclusion: PLM agenesis is a relatively uncommon anatomical finding. The absence rate observed in this study and the lack of significant differences between sexes or sides are consistent with previous imaging-based studies. No significant association was identified between PLM presence or absence and the 2D:4D digit ratio.

Keywords

digit ratio (2D:4D) , magnetic resonance imaging , palmaris longus absence , radiography , sex

References

• Bernardes A, Melo C, Pinheiro S. A combined variation of palmaris longus and flexor digitorum superficialis: case report and review of literature. Morphologie 2016;100:245–9.
• Cooper DW, Burns B. Anatomy, shoulder and upper limb, hand palmaris tendon. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023.
• Angelini Júnior LC, Angelini FB, de Oliveira BC, Soares SA, Angelini LC, Cabral RH. Use of the tendon of the palmaris longus muscle in surgical procedures: study on cadavers. Acta Orthop Bras 2012;20:226–9.
• Sankar KD, Bhanu PS, John SP. Incidence of agenesis of palmaris longus in the Andhra population of India. Indian J Plast Surg 2011;44:134–8.
• Johnson CC, Vutescu ES, Miller TT, Nwawka OK, Lee SK, Wolfe SW. Ultrasound determination of presence, length and diameter of the palmaris longus tendon. J Hand Surg Eur Vol 2018;43:948–53.
• Sebastin SJ, Lim AY. Clinical assessment of absence of the palmaris longus and its association with other anatomical anomalies – a Chinese population study. Ann Acad Med Singap 2006;35:249–53.
• Ioannis D, Anastasios K, Konstantinos N, Lazaros K, Georgios N. Palmaris longus muscle’s prevalence in different nations and interesting anatomical variations: review of the literature. J Clin Med Res 2015;7:825–30.
• Kapoor SK, Tiwari A, Kumar A, Bhatia R, Tantuway V, Kapoor S. Clinical relevance of palmaris longus agenesis: common anatomical aberration. Anat Sci Int 2008;83:45–8.
• Aliyu MN, Tiryakioglu M. The palmaris longus muscle: a surface study of the population of North Cyprus. Marmara Medical Journal 2021;34:267–73.
• Fidan N, Turk AC, Yetis EUM, Yucesoy C. Determination of congenital absence of palmaris longus tendon with clinical examination and ultrasonography. Surg Radiol Anat 2021;43:741–8.
• Alzahrani MT, Almalki MA, Al-Thunayan TA, Almohawis AH, Al Turki AT, Umedani L. Clinical assessment of the congenital absence of palmaris longus and flexor digitorum superficialis muscles in young Saudi population. Anat Res Int 2017, 5342497.
• Manning JT, Fink B. Digit ratio (2D:4D) and its relationship to foetal and maternal sex steroids: a mini-review. Early Hum Dev 2023;183:105799.
• Wang Y, Wang HL, Li YH, Zhu FL, Li SJ, Ni H. Using 2D: 4D digit ratios to determine motor skills in children. Eur Rev Med Pharmacol Sci 2016;20:806–9.
• Almashali M, Alekrish K, Shadid A. The use of 2D:4D digit ratio as a predictor of androgenetic alopecia: a review. Dermatol Pract Concept 2023;13:e2023237.
• Lee SHF, Aziz SA, Hamid M, Lim YC, Koh D, Chaw LL. 2D:4D ratio and autism spectrum disorder in Brunei Darussalam. J Autism Dev Disord 2021;51:4577–86.
• Fusar-Poli L, Rodolico A, Sturiale S, Carotenuto B, Natale A, Arillotta D, Siafis S, Signorelli MS, Aguglia E. Second-to-fourth digit ratio (2D:4D) in psychiatric disorders: a systematic review of case-control studies. Clin Psychopharmacol Neurosci 2021;19:26–45.
• Kalichman L, Batsevich V, Kobyliansky E. 2D:4D finger length ratio and radiographic hand osteoarthritis. Rheumatol Int 2018;38:865–70.
• Peters M, Mackenzie K, Bryden P. Finger length and distal finger extent patterns in humans. Am J Phys Anthropol 2002;117:209–17.
• Zhang W, Robertson J, Doherty S, Liu JJ, Maciewicz RA, Muir KR, Doherty M. Index to ring finger length ratio and the risk of osteoarthritis. Arthritis Rheum 2008:58:137–144.
• Zheng Z, Cohn MJ. Developmental basis of sexually dimorphic digit ratios. Proc Natl Acad Sci U S A 2011;108:16289–94.
• Lutchmaya S, Baron-Cohen S, Raggatt P, Knickmeyer R, Manning JT. 2nd to 4th digit ratios, fetal testosterone and estradiol. Early Hum Dev 2004;77:23–8.
• Voracek M, Dressler SG. Digit ratio (2D:4D) in twins: heritability estimates and evidence for a masculinized trait expression in women from opposite-sex pairs. Psychol Rep 2007;100:115–26.
• Pearce E, Wlodarski R, Machin A, Dunbar RIM. Associations between neurochemical receptor genes, 2D:4D, impulsivity and relationship quality. Biol Lett 2018;14:20180642.
• Manning JT, Bundred PE. The ratio of 2nd to 4th digit length: a new predictor of disease predisposition? Med Hypotheses 2000;54:855–7.
• Paul SN, Kato BS, Hunkin JL, Vivekanandan S, Spector TD. The big finger: the second to fourth digit ratio is a predictor of sporting ability in women. Br J Sports Med 2006;40:981–3.
• Hönekopp J, Schuster M. A meta-analysis on 2D: 4D and athletic prowess: substantial relationships but neither hand out-predicts the other. Personality and Individual Differences 2010;48:4–10.
• Pękala PA, Henry BM, Pękala JR, Skinningsrud B, Walocha JA, Bonczar M, Tomaszewski KA. Congenital absence of the palmaris longus muscle: a meta-analysis comparing cadaveric and functional studies. J Plast Reconstr Aesthet Surg 2017;70:1715–24.
• Kyung DS, Lee JH, Choi IJ, Kim DK. Different frequency of the absence of the palmaris longus according to assessment methods in a Korean population. Anat Cell Biol 2012;45:53–6.
• Venter G, Van Schoor AN, Bosman MC. Degenerative trends of the palmaris longus muscle in a South African population. Clin Anat 2014;27:222–6.
• Oluyemi Kayode A, Adesanya Olamide A, Odion Blessing I, Ukwenya Victor O. Incidence of palmaris longus muscle absence in Nigerian population. International Journal of Morphology 2008;26:305–8.
• Erić M, Krivokuća D, Savović S, Leksan I, Vucinić N. Prevalence of the palmaris longus through clinical evaluation. Surg Radiol Anat 2010;32:357–61.
• Cetin A, Genc M, Sevil S, Coban YK. Prevalence of the palmaris longus muscle and its relationship with grip and pinch strength: a study in a Turkish pediatric population. Hand (N Y) 2013;8:215–20.
• Holzgrefe RE, Anastasio AT, Farley KX, Daly CA, Mason AR, Gottschalk MB. Detection of the palmaris longus tendon: physical examination versus sonography. J Hand Surg Eur Vol 2019;44:800–4.