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Magnetic Resonance Imaging Evaluation of the DistalBiceps Tendon and Lacertus Fibrosus at the Elbow:A Study of Normal Anatomy and VariantsKirthi Sathyakumar 1 Aravind Murugesan 1 Madhu Sowmitha Pachipala 1Sundara Raja Perumal 11 Department of Radiology, SRM Medical College Hospital andResearch Centre, Chengalpattu, Tamil Nadu, IndiaIndian J Radiol ImagingAddress for correspondence Aravind Murugesan, MBBS, MD(Radiology), Department of Radiology, SRM Medical College Hospitaland Research Centre, Potheri, Chengalpattu, Tamil Nadu, India –603203 (e-mail: aravind.murug@gmail.com).IntroductionThe biceps brachii (BB) muscle inserts distally via a primarytendon to the radial tuberosity and an aponeurotic expan-sion known as the lacertus f i brosus (LF), also called thebicipital aponeurosis. This f i brous structure spans mediallyacrossthe antecubital fossa, merging with theforearm f l exorfascia. 1,2 Theirproximitytocriticalneurovascularstructures,the median nerve (MN) and brachial artery (BrA), renders itclinically signif i cant in cases of entrapment syndromes.Keywords? MRI? lacertus fibrosus? bicipital aponeurosis? biceps brachii? distal biceps tendonAbstract Background The distal biceps brachii tendon (BB) and its aponeurotic extension, thelacertus f i brosus (LF), represent important anatomical structures of the elbow withfunctional and clinical relevance.Purpose The objective of this study is to describetheappearance, morphometry, andanatomical variations of the LF and distal biceps tendon on magnetic resonanceimaging (MRI).Materials and Methods Retrospective review of the MRI elbow joints of 81 patients.The presence and morphology of the LFand BB were analyzed utilizing high-resolutionMRI and referencing anatomical classif i cations and morphometric parameters.Results The study included 81 patients (32 females, 49 males; mean age 33.7?13.4years). The LF was present in 87.7% and absent in 12.3% of elbows. Mean LF measure-ments were: thickness 0.63?0.16mm, width 17.54?4.66mm, and length30.55?8.37mm. In 77.5%, the brachial artery lay anterior to the median nerve; in19.7%, they were equidistant from the LF, and in 2.8%, the median nerve lay anterior tothe brachial artery. Type I BB tendon was most common (n¼74), with Type II (n¼5)and Type III (n¼2). Mean BB tendon length and thickness were 59.25?11.96mm and3.51?0.70mm, respectively. BB tendon thickness was the strongest predictor of LFabsence(areaunder thecurve [AUC]:0.698),whileaddingvariablesliketendonlength,age, and sex did not signif i cantly enhance discrimination (AUC: 0.714).Conclusion TheLFandanatomicalvariationsofthedistalBBtendonattheelbowareoftenoverlooked. We emphasize the relevance of understanding normal variants that could aid inaccurate diagnosis and facilitate the recognition of possible entrapment syndromes.DOI https://doi.org/10.1055/s-0046-1820518.ISSN 0971-3026.© 2026. Indian Radiological Association. All rights reserved.This is an open access article published by Thieme under the terms of theCreative Commons Attribution-NonDerivative-NonCommercial-License,permitting copying and reproduction so long as the original work is givenappropriate credit. Contents may not be used for commercial purposes, oradapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/)Thieme Medical and Scientif i c Publishers Private Limited, A-13A,GraphixTower1,6thf l oor,Sector62,Noida201309,UttarPradesh,IndiaTHIEMEOriginal ArticleArticle published online: 2026-05-11