The accessory brachioradialis muscle (brachioradialis accessorius): Prevalence of a rare variant with possible implications for radial nerve compression

The accessory brachioradialis muscle (brachioradialis accessorius): Prevalence of a rare variant with possible implications for radial nerve compression | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article The accessory brachioradialis muscle (brachioradialis accessorius): Prevalence of a rare variant with possible implications for radial nerve compression George Triantafyllou, Krzysztof Koptas, Nicol Zielinska, Maria Piagkou, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4675099/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 13 Aug, 2024 Read the published version in Surgical and Radiologic Anatomy → Version 1 posted 11 You are reading this latest preprint version Abstract Purpose The brachioradialis muscle (BR) belongs to the radial forearm muscles and contributes to the elbow flexion. Accessory brachioradialis muscle (ABR) or brachioradialis “accessorius” represents an uncommon BR variant, not been enough studied. The present study investigates the incidence of the ABR variant, along with its origin, insertion, and innervation. Materials: Eighty-three (83) upper limbs were meticulously dissected at the arm, forearm, and cubital fossa to investigate the ABR presence. When the variant muscle was identified, morphometric measurements were obtained. Results The ABR was identified in two upper limbs (2/83, 2.4%), in a male cadaver, bilaterally. Its origin was located along with the typical BR, and its insertion was identified into the anterior surface of the radius. The radial nerve supplied the ABR, having a course posteriorly to it (in a deeper layer). Conclusions In the current study, the variant muscle was observed in 2.4%, while the ABR reported incidence is recorded between 0.5–2.8%. Radial nerve compression, at the forearm, is not an uncommon entrapment neuropathy. The relationship between the radial nerve and the ABR could precipitate radial neuropathy. brachioradialis accessorius accessory brachioradialis muscle variation radial nerve compression Figures Figure 1 Introduction Typically, the brachioradialis muscle (BR), a radial forearm muscle, originates from the upper two-thirds of the lateral epicondylar ridge, and the anterior surface of the lateral intermuscular septum and inserts onto the lateral side of the base of the styloid process of the radius [ 14 , 15 ]. It is innervated by the radial nerve (RN), which courses between the BR and brachialis to enter the anterior forearm compartment [ 14 ]. The BR's main function is the elbow flexion [43]. Occasionally, the muscle is fused with the brachialis and deltoid muscles in the arm, and with the extensor carpi radialis longus and abductor pollicis longus in the forearm [ 8 , 12 ]. Other BR variants include the splitting of its muscular or tendinous part [ 4 , 16 ] and the concomitant variant course of the RN superficial branch in between the BR split muscular or tendinous part that may cause RN entrapment also known as Wartenberg’s syndrome [ 4 , 16 ]. A very uncommon muscle variant that has been barely studied is the accessory BR (ABR), the so-called brachioradialis “accessorius” [ 11 ]. The ABR variant has been identified mainly incidentally and has been systematically studied in a few papers with a calculated incidence varying between 0.5–2.8% [ 1 , 3 , 11 ]. Rodriguez-Niedenfuhr et al. [ 11 ] in their detailed morphological study defined the ABR as a separate supernumerary muscle in the lateral cubital fossa originating from the humerus or as a BR which is inserted into the radius, the pronator teres, or the supinator muscle, with innervation by the RN, so characterized as a derivative of the humero-radialis group [ 11 ]. The current study identifies the ABR and characterizes its origin, insertion, innervation, and relationship with the RN. The embryological development, comparative anatomy, and possible clinical significance are further discussed to enhance the current gross anatomical study. Materials and Methods Eighty-three (42 right and 41 left) 10% formalin-fixed upper limbs of both genders, were examined. The sample (Central European population) was derived from the Department of Anatomical Dissection and Donation of the Medical University of Lodz. All the upper limbs were free of visible trauma and previous surgery. Dissection began with the removal of the skin and superficial fascia of the arm and forearm lateral compartment. The brachialis, BR, biceps, and triceps along with the RN branching pattern were visualized. An adequate dissection of the cubital fossa was performed for the identification of the ABR presence. After identifying the variant muscle, we investigated the following parameters: ABR origin and insertion Relationship with the RN and the cubital fossa neurovascular structures Morphometric parameters of ABR (length, width, and thickness). An electronic digital caliper was used for all measurements ( Mitutoyo Corporation, Kawasaki-shi, Kanagawa, Japan ), and each measurement was performed twice with an accuracy of up to 0.1 mm. Results The typical BR was identified in all specimens (83 upper limbs, 100%). An ABR was recorded in two upper limbs (2/83, 2.4%) of a male cadaver, bilaterally. In both cases, the atypical muscle’s origin was along with the typical BR, from the lateral supracondylar humeral ridge, and its insertion into the proximal third of the anterior surface of the radius. The ABR innervation was derived by the RN. In both cases, the RN coursed between the brachialis and the ABR, while at the cubital fossa, the nerve passed posteriorly to the variant muscle (Fig. 1 ). The morphometric parameters of the two cases are summarized in Table 1 . Table 1 Morphometric parameters of the accessory brachioradialis muscle (ABR) by side. All values are expressed in mm. PA- proximal attachment, and DA- distal attachment. The width was expressed as the lateromedial distance, the thickness was expressed as an anteroposterior distance, and length as the craniocaudal distance from the uppermost point of origin to the lowermost insertion point Parameters PA (width) PA (thickness) ABR Length DA (width) DA (thickness) Left side 24.73 0.68 70.10 30.44 1.24 Right side 20.86 1.37 96.87 8.62 0.68 Discussion Embryological development and comparative anatomy of the brachioradialis muscle During embryological development, the extensor forearm muscles differentiate before the flexors. In about 11-mm embryo length, a common extensor premuscle mass differentiates into three groups. The first group that develops into the extensors digitorum communis, carpi ulnaris, and digiti minimi, corresponds to the largest and most superficial group. The second group differentiates to BR, and extensors carpi radialis brevis and longus [ 7 ]. Therefore, alterations during this differentiation process from a common premuscular mass to distinct muscles could potentially give accessory muscles, such as the ABR. Except for the embryological background of the typical BR, the muscle’s comparative anatomy is essential to better understand how an accessory muscle may develop. In some mammals, such as the Myrmecophagidae , the BR was considered to be composed of two heads, while recent studies have proved that the two heads have an independent origin, insertion, and innervation; therefore, it has been proposed that the BR typically coexists with the ABR [ 10 ]. Morphological variability of the accessory brachioradialis (ABR) In the current study, the ABR was identified in 2.4%, with a bilateral presence in a male cadaver. The origin was adjacent to the typical BR, and the insertion onto the anterior surface of the proximal third of the radius. The innervation was provided by the RN that coursed posteriorly to the ABR. After a detailed literature search, only a few studies and case reports refer to the ABR variant. Recently, rare muscle variants of the upper limb have been studied to enhance the current knowledge of human morphological anatomy [ 18 ]. The ABR is considered a rare variant, with very few studies referring to its presence [ 2 , 3 , 5 , 6 , 11 , 13 ]. Dawson [ 2 ] was the first to describe the ABR variant. The old studies conducted by Carrington et al. [ 1 ] and Gruber [ 3 ] recorded an incidence ranging between 0.5-1%, while the newer morphological study by Rodrigiuez-Niedefuhr et al. [ 11 ] identified a relatively higher incidence (2.8%). The ABR origin is relatively constant, proximal to the BR typical origin, while Rodriguez-Niedenfuhr et al. [ 11 ] identified, in a few cases, its origin from the humeral condylar ridge, distally to BR. Less frequent origin is considered when the ABR originates from the typical BR [ 2 , 6 , 11 ]. Tountas and Bergman [ 15 ] reported an ABR termed supinator longus accessorius or BR brevis (Gruber [ 3 ]) was described as arising adjacent to BR, inserting onto the radial tuberosity, and acting as a true supinator, or inserting into the supinator or the tendon of pronator teres or onto the ulna. On the other hand, the ABR insertion is variable, including more frequently the radial tuberosity, along with the biceps brachii tendon, and less frequently the anterior surface of the radius, the supinator muscle, the pronator teres or rarely the sigmoid cavity of the ulna [ 2 , 6 , 11 ]. Hence, in the current study, the origin followed the current literature, while the insertion into the anterior surface of the radius is considered uncommon. Furthermore, in the current study, the ABR presence was bilaterally identified in a male cadaver. Such bilateral presence was also identified by Rodriguez-Niedenfuhr's [ 11 ] study, where they identified bilateral appearance in two cadavers. Lastly, its innervation has been studied only in the Rodriguez-Niedenfuhr et al. [ 11 ] study, which supported that the ABR was supplied by RN branches, similar to the current study. Except from ABR, BR variants could also be detected, such as duplicated muscle bellies or tendons. Herma et al. [ 4 ] presented a report of a two-bellied BR coexisting with a duplicated RN superficial branch, predisposing to radial neuropathy. Nambi and Dhiwakar [ 9 ] identified a second aberrant BR muscular belly during the radial artery forearm flap. Except for the muscular part, the tendinous part could be presented with variant forms. Turkof et al. [ 16 ] studied the BR tendon split in 75 cadavers (150 upper limbs) and identified the split tendon in 9 upper limbs (6%). Interestingly, in 5 of them (3.33%), the RN superficial branch coursed between the two slips, indicating a possible site of compression [ 16 ]. Sanudo et al. [ 12 ], among 80 upper limbs, identified an BR uncommon insertion into the base of the third metacarpal bone. Clinical implications of the brachioradialis accessorius The BR is considered a possible site for RN compression, particularly when considering the muscle’s morphological variability [ 17 ]. In the current literature, few clinical cases refer to radial neuropathy due to the BR variants. Spinner and Spinner [ 13 ] intraoperatively identified the RN superficial branch running inferiorly to an ABR, causing progressive numbness in the right thumb dorsal aspect. Closely to Spinner and Spinner [ 13 ], Kravarski et al. [ 5 ], intraoperatively, identified another ABR form adjacent to the typical BR. Due to this close relationship between the ABR and RN superficial branch, the variant muscle could cause entrapment, the so-called Wartenberg’s syndrome, or cheiralgia paresthetica [ 5 ]. In the current study, the RN was coursing posteriorly to the atypical BR, and this course could potentially be an entrapment site. Closely to the current results, Rodriguez-Niedenfuhr et al. [ 11 ] observed a similar course of the RN posteriorly to the ABR. Muscle hypertrophy could precipitate this entrapment [ 4 ]. Nevertheless, surgeons should be aware of this variant while performing a radial forearm free flap to not confuse intraoperatively [ 5 ]. Limitations The present study has a few limitations. Firstly, a higher sample would have been desirable (n = 83), particularly a mixed sample not exclusively derived from a specific (Poland, Central European) population, permitting us to generalize our findings. Wider populations and more extensive studies will enhance the current knowledge about the ABR variant. Also, the arterial supply and the relationship of the variant muscle with vascular structures were not possible to study in the two identified specimens. Conclusion The ABR is considered a very uncommon variation of the BR and was identified in 2.4% of the present study, as a symmetrical (bilateral) finding. The variant muscle’s origin included the lateral supracondylar ridge, and the insertion was into the anterior compartment of the radius. The RN innervated the muscle and coursed posterior to the ABR. Clinicians should bear in mind this variant and include it during RN compression differential diagnosis. Declarations Ethical approval and consent to participate The cadavers belonged to the Department of Anatomical Dissection and Donation, Medical University of Lodz. Availability of data and materials Please contact authors for data requests (George Triantafyllou - email address: [email protected] ). Competing interests The authors declare that they have no competing interests. Funding The authors have no financial or personal relationship with any third party whose interests could be positively or negatively influenced by the article’s content. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Authors’ contribution George Triantafyllou and Krzysztof Koptas equally contributed to this paper, as first-authors. George Triantafyllou – student – project development, data collection and management, data analysis, and manuscript writing. Krzysztof Koptas – student – data collection, data analysis, and manuscript editing. Nicol Zielinska – student – data collection, data analysis, and manuscript editing. Maria Piagkou (DDS, MD, PhD, MSc) – professor – data analysis and manuscript editing. Łukasz Olewnik (D.P.T., PhD) – associate professor – supervision, data analysis, and manuscript editing. All authors have read and approved the manuscript. ACKNOWLEDGMENTS The authors sincerely thank those who donated their bodies to science so that anatomical research could be performed. The knowledge gained from such research can immensely benefit patient care, and these donors and their families deserve our highest gratitude. References Carrington RE, Horrocks P, Hale White W (1883) Abnormalities observed in the dissecting room of Guy’s Hospital during the sessions 1880–1881 and 1881–1882. Guy’s Hospital Reports 41: 57–81 Dawson M (1822) Sketch of two small supernumerary muscles of the arm. Edinb Med Surg J 18:82–83 Gruber W (1848) Seltene Beobachtungen aus dem Gebiete der menschlichen Anatomie. Archiv fur Anatomie und Physiologie und wissenschaftliche Medizin 412: 433 Herma T, Baca V, Yershov D, Kachlik D (2017) A case of a duplicated superficial branch of radial nerve and a two-bellied brachioradialis muscle presenting a potential entrapment syndrome. Surg Radiol Anat 39:451–454. https://doi.org/10.1007/s00276-016-1732-8 Kravarski M, Goerres GW, Antoniadis A, Guenkel S (2020) Supernumerary brachioradialis - Anatomical variation with magnetic resonance imaging findings: A case report. World J Orthop 11:411–417. https://doi.org/10.5312/wjo.v11.i9.411 Lauth EA (1830) Varietes dans la distribution des muscles de l’homme. Memoires de la Societe d ’Histoire Naturelle de Strasbourg 1:65–69 Lewis WH (1910) XII. THE DEVELOPMENT OF THE MUSCULAR SYSTEM. BY WARREN H. LEWIS, JOHNS HOPKINS UNIVERSITY, BALTIMORE, MD., USA. Manual of human embryology 1: 454 Macalister A (1875) Additional Observations on Muscular Anomalies in Human Anatomy. (Third Series) With a Catalogue of the Principal Muscular Variations Hitherto Published. Trans Royal Ir Acad 25:1–134 Nambi GI, Dhiwakar M (2016) Variable Presentation of Brachioradialis Muscle During Radial Artery Forearm Free Flap Harvest—An Accessory Distal Belly. J Hand Microsurg 06:35–36. https://doi.org/10.1007/s12593-012-0080-0 Polania-Guzmán PV, Vélez-García JF (2019) Gross anatomical adaptations of the craniolateral forearm muscles in Tamandua mexicana (Xenarthra: Myrmecophagidae): development of accessory muscles and rete mirabile for its arterial supply. Heliyon 5:e02179. https://doi.org/10.1016/j.heliyon.2019.e02179 Rodriguez-Niedenfuhr M, Vazquez T, Parkin I, Nearn L, Sanudo JR (2001) Incidence and morphology of the brachioradialis accessorius muscle. J Anat 199:353–355. https://doi.org/10.1046/j.1469-7580.2001.19930353.x Sañudo JR, Young RC, Abrahams P (1996) Brachioradialis muscle inserting on the third metacarpal. J Anat 188(3):733–734 Spinner RJ, Spinner M (1996) superficial radial nerve compression at the elbow due to an accessory brachioradialis muscle: A case report. J Hand Surg Am 21:369–372. https://doi.org/10.1016/S0363-5023(96)80346-7 Standring S (2016) Gray's anatomy. Elsevier/Churchill Livingstone, New York Tountas CP, Bergmann RA (1993) Anatomic Variations of the Upper Extremity. Churchill Livingstone, New York Turkof E, Puig S, Choi MSS, Schilhan R, Millesi H, Firbas W (1994) Superficial Branch of the Radial Nerve Emerging between Two Slips of a Split Brachioradialis Muscle Tendon: A Variation of Possible Clinical Relevance. Cells Tissues Organs 150:232–236. https://doi.org/10.1159/000147624 Węgiel A, Karauda P, Zielinska N, Tubbs RS, Olewnik Ł (2023) Radial nerve compression: anatomical perspective and clinical consequences. Neurosurg Rev 46:53. https://doi.org/10.1007/s10143-023-01944-2 Zielinska N, Duparc F, Polguj M, Borowski A, Olewnik Ł (2022) A proposal for a new classification of the Coracobrachialis longus: A rare case or a new, distinct muscle? Ann Anat 239:151825. https://doi.org/10.1016/j.aanat.2021.151825 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 13 Aug, 2024 Read the published version in Surgical and Radiologic Anatomy → Version 1 posted Editorial decision: Revision requested 30 Jul, 2024 Reviews received at journal 21 Jul, 2024 Reviews received at journal 15 Jul, 2024 Reviews received at journal 12 Jul, 2024 Reviewers agreed at journal 10 Jul, 2024 Reviewers agreed at journal 08 Jul, 2024 Reviewers agreed at journal 04 Jul, 2024 Reviewers invited by journal 03 Jul, 2024 Editor assigned by journal 03 Jul, 2024 Submission checks completed at journal 03 Jul, 2024 First submitted to journal 02 Jul, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4675099","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":329685312,"identity":"016adf27-e386-4819-9761-23b9eaf907af","order_by":0,"name":"George Triantafyllou","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABAElEQVRIiWNgGAWjYJCDhAMfKoAUM3MD0VoePpxxBqSFkWgtjI+NOdvADPxa5N2bj338UnFPTr69OU2acV5tNH87UMuPim04tRieOZY8W+ZMsbHBmWNp0oXbjufOOMzYwNhz5jZuLTNyjJkl2xISN0jkpEnP3HYstwGohZmxDY+W+W+AWv4lJM6f//6bNO+cY7nzCWmRl+AxZvzYkJDYcIMh2Zi3oSZ3AyEtBjxpycwMxxKAfklIfDjj2IHcjUAtB/H5Rb798GHGHzUJwBA7AIzKmrrceecPH3zwowKPLQeAcceD4B8GkwdwqgfZ0gCMuh8Ifh0+xaNgFIyCUTBCAQBZLWEjFkKnWQAAAABJRU5ErkJggg==","orcid":"","institution":"Department of Anatomy, School of Medicine, Faculty of Health Sciences, National and Kapodistrian University of Athens","correspondingAuthor":true,"prefix":"","firstName":"George","middleName":"","lastName":"Triantafyllou","suffix":""},{"id":329685313,"identity":"47914095-6e6b-4955-b929-402eda3c9b03","order_by":1,"name":"Krzysztof Koptas","email":"","orcid":"","institution":"Department of Clinical Anatomy, Masovian Academy in Plock","correspondingAuthor":false,"prefix":"","firstName":"Krzysztof","middleName":"","lastName":"Koptas","suffix":""},{"id":329685317,"identity":"3acadb57-c5e0-4b1f-9e1e-052d8a1f35a8","order_by":2,"name":"Nicol Zielinska","email":"","orcid":"","institution":"Department of Clinical Anatomy, Masovian Academy in Plock","correspondingAuthor":false,"prefix":"","firstName":"Nicol","middleName":"","lastName":"Zielinska","suffix":""},{"id":329685319,"identity":"989c947a-397b-4cfe-8830-d81a0b5438a1","order_by":3,"name":"Maria Piagkou","email":"","orcid":"","institution":"Department of Anatomy, School of Medicine, Faculty of Health Sciences, National and Kapodistrian University of Athens","correspondingAuthor":false,"prefix":"","firstName":"Maria","middleName":"","lastName":"Piagkou","suffix":""},{"id":329685320,"identity":"ab40ed48-e33f-4785-b8bc-08d29f8dbe12","order_by":4,"name":"Łukasz Olewnik","email":"","orcid":"","institution":"Department of Clinical Anatomy, Masovian Academy in Plock","correspondingAuthor":false,"prefix":"","firstName":"Łukasz","middleName":"","lastName":"Olewnik","suffix":""}],"badges":[],"createdAt":"2024-07-02 14:51:24","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4675099/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4675099/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00276-024-03462-2","type":"published","date":"2024-08-13T15:57:38+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":61076161,"identity":"59dff5ec-ecfa-41a0-b8fe-c267757d3705","added_by":"auto","created_at":"2024-07-25 09:31:25","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":3687975,"visible":true,"origin":"","legend":"\u003cp\u003eThe accessory brachioradialis (ABR) variant muscle. BM- brachialis muscle, RN- radial nerve, BR- brachioradialis muscle, and ECR- extensor carpi radialis.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-4675099/v1/c1a3a25a5f495845504e3a02.png"},{"id":63071421,"identity":"26228146-06b4-4a07-9bef-4bcf4b8f3bbc","added_by":"auto","created_at":"2024-08-22 20:07:04","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4948417,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4675099/v1/8861a100-c185-4d80-8fd0-93e508676dda.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"The accessory brachioradialis muscle (brachioradialis accessorius): Prevalence of a rare variant with possible implications for radial nerve compression","fulltext":[{"header":"Introduction","content":"\u003cp\u003eTypically, the brachioradialis muscle (BR), a radial forearm muscle, originates from the upper two-thirds of the lateral epicondylar ridge, and the anterior surface of the lateral intermuscular septum and inserts onto the lateral side of the base of the styloid process of the radius [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. It is innervated by the radial nerve (RN), which courses between the BR and brachialis to enter the anterior forearm compartment [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. The BR's main function is the elbow flexion [43]. Occasionally, the muscle is fused with the brachialis and deltoid muscles in the arm, and with the extensor carpi radialis longus and abductor pollicis longus in the forearm [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Other BR variants include the splitting of its muscular or tendinous part [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] and the concomitant variant course of the RN superficial branch in between the BR split muscular or tendinous part that may cause RN entrapment also known as Wartenberg\u0026rsquo;s syndrome [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. A very uncommon muscle variant that has been barely studied is the accessory BR (ABR), the so-called brachioradialis \u0026ldquo;accessorius\u0026rdquo; [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The ABR variant has been identified mainly incidentally and has been systematically studied in a few papers with a calculated incidence varying between 0.5\u0026ndash;2.8% [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Rodriguez-Niedenfuhr et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] in their detailed morphological study defined the ABR as a separate supernumerary muscle in the lateral cubital fossa originating from the humerus or as a BR which is inserted into the radius, the pronator teres, or the supinator muscle, with innervation by the RN, so characterized as a derivative of the humero-radialis group [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe current study identifies the ABR and characterizes its origin, insertion, innervation, and relationship with the RN. The embryological development, comparative anatomy, and possible clinical significance are further discussed to enhance the current gross anatomical study.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003eEighty-three (42 right and 41 left) 10% formalin-fixed upper limbs of both genders, were examined. The sample (Central European population) was derived from the Department of Anatomical Dissection and Donation of the Medical University of Lodz. All the upper limbs were free of visible trauma and previous surgery. Dissection began with the removal of the skin and superficial fascia of the arm and forearm lateral compartment. The brachialis, BR, biceps, and triceps along with the RN branching pattern were visualized. An adequate dissection of the cubital fossa was performed for the identification of the ABR presence. After identifying the variant muscle, we investigated the following parameters:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eABR origin and insertion\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eRelationship with the RN and the cubital fossa neurovascular structures\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eMorphometric parameters of ABR (length, width, and thickness).\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eAn electronic digital caliper was used for all measurements (\u003cem\u003eMitutoyo Corporation, Kawasaki-shi, Kanagawa, Japan\u003c/em\u003e), and each measurement was performed twice with an accuracy of up to 0.1 mm.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eThe typical BR was identified in all specimens (83 upper limbs, 100%). An ABR was recorded in two upper limbs (2/83, 2.4%) of a male cadaver, bilaterally. In both cases, the atypical muscle\u0026rsquo;s origin was along with the typical BR, from the lateral supracondylar humeral ridge, and its insertion into the proximal third of the anterior surface of the radius. The ABR innervation was derived by the RN. In both cases, the RN coursed between the brachialis and the ABR, while at the cubital fossa, the nerve passed posteriorly to the variant muscle (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The morphometric parameters of the two cases are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMorphometric parameters of the accessory brachioradialis muscle (ABR) by side. All values are expressed in mm. PA- proximal attachment, and DA- distal attachment. The width was expressed as the lateromedial distance, the thickness was expressed as an anteroposterior distance, and length as the craniocaudal distance from the uppermost point of origin to the lowermost insertion point\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameters\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePA\u003c/p\u003e \u003cp\u003e(width)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePA\u003c/p\u003e \u003cp\u003e(thickness)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eABR Length\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDA\u003c/p\u003e \u003cp\u003e(width)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eDA\u003c/p\u003e \u003cp\u003e(thickness)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eLeft side\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e24.73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e70.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.24\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eRight side\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e96.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e8.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.68\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eEmbryological development and comparative anatomy of the brachioradialis muscle\u003c/h2\u003e \u003cp\u003eDuring embryological development, the extensor forearm muscles differentiate before the flexors. In about 11-mm embryo length, a common extensor premuscle mass differentiates into three groups. The first group that develops into the extensors digitorum communis, carpi ulnaris, and digiti minimi, corresponds to the largest and most superficial group. The second group differentiates to BR, and extensors carpi radialis brevis and longus [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Therefore, alterations during this differentiation process from a common premuscular mass to distinct muscles could potentially give accessory muscles, such as the ABR.\u003c/p\u003e \u003cp\u003eExcept for the embryological background of the typical BR, the muscle\u0026rsquo;s comparative anatomy is essential to better understand how an accessory muscle may develop. In some mammals, such as the \u003cem\u003eMyrmecophagidae\u003c/em\u003e, the BR was considered to be composed of two heads, while recent studies have proved that the two heads have an independent origin, insertion, and innervation; therefore, it has been proposed that the BR typically coexists with the ABR [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eMorphological variability of the accessory brachioradialis (ABR)\u003c/h2\u003e \u003cp\u003eIn the current study, the ABR was identified in 2.4%, with a bilateral presence in a male cadaver. The origin was adjacent to the typical BR, and the insertion onto the anterior surface of the proximal third of the radius. The innervation was provided by the RN that coursed posteriorly to the ABR. After a detailed literature search, only a few studies and case reports refer to the ABR variant. Recently, rare muscle variants of the upper limb have been studied to enhance the current knowledge of human morphological anatomy [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe ABR is considered a rare variant, with very few studies referring to its presence [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Dawson [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] was the first to describe the ABR variant. The old studies conducted by Carrington et al. [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] and Gruber [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] recorded an incidence ranging between 0.5-1%, while the newer morphological study by Rodrigiuez-Niedefuhr et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] identified a relatively higher incidence (2.8%). The ABR origin is relatively constant, proximal to the BR typical origin, while Rodriguez-Niedenfuhr et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] identified, in a few cases, its origin from the humeral condylar ridge, distally to BR. Less frequent origin is considered when the ABR originates from the typical BR [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Tountas and Bergman [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] reported an ABR termed supinator longus accessorius or BR brevis (Gruber [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]) was described as arising adjacent to BR, inserting onto the radial tuberosity, and acting as a true supinator, or inserting into the supinator or the tendon of pronator teres or onto the ulna.\u003c/p\u003e \u003cp\u003eOn the other hand, the ABR insertion is variable, including more frequently the radial tuberosity, along with the biceps brachii tendon, and less frequently the anterior surface of the radius, the supinator muscle, the pronator teres or rarely the sigmoid cavity of the ulna [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Hence, in the current study, the origin followed the current literature, while the insertion into the anterior surface of the radius is considered uncommon. Furthermore, in the current study, the ABR presence was bilaterally identified in a male cadaver. Such bilateral presence was also identified by Rodriguez-Niedenfuhr's [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] study, where they identified bilateral appearance in two cadavers. Lastly, its innervation has been studied only in the Rodriguez-Niedenfuhr et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] study, which supported that the ABR was supplied by RN branches, similar to the current study.\u003c/p\u003e \u003cp\u003eExcept from ABR, BR variants could also be detected, such as duplicated muscle bellies or tendons. Herma et al. [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] presented a report of a two-bellied BR coexisting with a duplicated RN superficial branch, predisposing to radial neuropathy. Nambi and Dhiwakar [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] identified a second aberrant BR muscular belly during the radial artery forearm flap. Except for the muscular part, the tendinous part could be presented with variant forms. Turkof et al. [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] studied the BR tendon split in 75 cadavers (150 upper limbs) and identified the split tendon in 9 upper limbs (6%). Interestingly, in 5 of them (3.33%), the RN superficial branch coursed between the two slips, indicating a possible site of compression [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Sanudo et al. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], among 80 upper limbs, identified an BR uncommon insertion into the base of the third metacarpal bone.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eClinical implications of the brachioradialis accessorius\u003c/h2\u003e \u003cp\u003eThe BR is considered a possible site for RN compression, particularly when considering the muscle\u0026rsquo;s morphological variability [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. In the current literature, few clinical cases refer to radial neuropathy due to the BR variants. Spinner and Spinner [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] intraoperatively identified the RN superficial branch running inferiorly to an ABR, causing progressive numbness in the right thumb dorsal aspect. Closely to Spinner and Spinner [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], Kravarski et al. [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], intraoperatively, identified another ABR form adjacent to the typical BR. Due to this close relationship between the ABR and RN superficial branch, the variant muscle could cause entrapment, the so-called Wartenberg\u0026rsquo;s syndrome, or cheiralgia paresthetica [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. In the current study, the RN was coursing posteriorly to the atypical BR, and this course could potentially be an entrapment site. Closely to the current results, Rodriguez-Niedenfuhr et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] observed a similar course of the RN posteriorly to the ABR. Muscle hypertrophy could precipitate this entrapment [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Nevertheless, surgeons should be aware of this variant while performing a radial forearm free flap to not confuse intraoperatively [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eLimitations\u003c/h2\u003e \u003cp\u003eThe present study has a few limitations. Firstly, a higher sample would have been desirable (n\u0026thinsp;=\u0026thinsp;83), particularly a mixed sample not exclusively derived from a specific (Poland, Central European) population, permitting us to generalize our findings. Wider populations and more extensive studies will enhance the current knowledge about the ABR variant. Also, the arterial supply and the relationship of the variant muscle with vascular structures were not possible to study in the two identified specimens.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe ABR is considered a very uncommon variation of the BR and was identified in 2.4% of the present study, as a symmetrical (bilateral) finding. The variant muscle\u0026rsquo;s origin included the lateral supracondylar ridge, and the insertion was into the anterior compartment of the radius. The RN innervated the muscle and coursed posterior to the ABR. Clinicians should bear in mind this variant and include it during RN compression differential diagnosis.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthical approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe cadavers belonged to the Department of Anatomical Dissection and Donation, Medical University of Lodz.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePlease contact authors for data requests (George Triantafyllou - email address:\u0026nbsp;[email protected]).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no financial or personal relationship with any third party whose interests could be positively or negatively influenced by the article\u0026rsquo;s content. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; contribution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eGeorge Triantafyllou and Krzysztof Koptas equally contributed to this paper, as first-authors.\u003c/p\u003e\n\u003cp\u003eGeorge Triantafyllou \u0026ndash; student \u0026ndash; project development, data collection and management, data analysis, and manuscript writing.\u003c/p\u003e\n\u003cp\u003eKrzysztof Koptas \u0026ndash; student \u0026ndash; data collection, data analysis, and manuscript editing.\u003c/p\u003e\n\u003cp\u003eNicol Zielinska \u0026ndash; student \u0026ndash; data collection, data analysis, and manuscript editing.\u003c/p\u003e\n\u003cp\u003eMaria Piagkou (DDS, MD, PhD, MSc) \u0026ndash; professor \u0026ndash; data analysis and manuscript editing.\u003c/p\u003e\n\u003cp\u003eŁukasz Olewnik (D.P.T., PhD) \u0026ndash; associate professor \u0026ndash; supervision, data analysis, and manuscript editing.\u003c/p\u003e\n\u003cp\u003eAll authors have read and approved the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eACKNOWLEDGMENTS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors sincerely thank those who donated their bodies to science so that anatomical research could be performed. The knowledge gained from such research can immensely benefit patient care, and these donors and their families deserve our highest gratitude.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eCarrington RE, Horrocks P, Hale White W (1883) Abnormalities observed in the dissecting room of Guy\u0026rsquo;s Hospital during the sessions 1880\u0026ndash;1881 and 1881\u0026ndash;1882. Guy\u0026rsquo;s Hospital Reports 41: 57\u0026ndash;81\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDawson M (1822) Sketch of two small supernumerary muscles of the arm. Edinb Med Surg J 18:82\u0026ndash;83\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGruber W (1848) Seltene Beobachtungen aus dem Gebiete der menschlichen Anatomie. 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Churchill Livingstone, New York\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTurkof E, Puig S, Choi MSS, Schilhan R, Millesi H, Firbas W (1994) Superficial Branch of the Radial Nerve Emerging between Two Slips of a Split Brachioradialis Muscle Tendon: A Variation of Possible Clinical Relevance. Cells Tissues Organs 150:232\u0026ndash;236. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1159/000147624\u003c/span\u003e\u003cspan address=\"10.1159/000147624\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWęgiel A, Karauda P, Zielinska N, Tubbs RS, Olewnik Ł (2023) Radial nerve compression: anatomical perspective and clinical consequences. 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Ann Anat 239:151825. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.aanat.2021.151825\u003c/span\u003e\u003cspan address=\"10.1016/j.aanat.2021.151825\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"surgical-and-radiologic-anatomy","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"sara","sideBox":"Learn more about [Surgical and Radiologic Anatomy](http://link.springer.com/journal/276)","snPcode":"276","submissionUrl":"https://submission.nature.com/new-submission/276/3","title":"Surgical and Radiologic Anatomy","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"brachioradialis accessorius, accessory brachioradialis muscle, variation, radial nerve compression","lastPublishedDoi":"10.21203/rs.3.rs-4675099/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4675099/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003ePurpose\u003c/h2\u003e \u003cp\u003eThe brachioradialis muscle (BR) belongs to the radial forearm muscles and contributes to the elbow flexion. Accessory brachioradialis muscle (ABR) or brachioradialis \u0026ldquo;accessorius\u0026rdquo; represents an uncommon BR variant, not been enough studied. The present study investigates the incidence of the ABR variant, along with its origin, insertion, and innervation.\u003c/p\u003e\u003ch2\u003eMaterials:\u003c/h2\u003e \u003cp\u003eEighty-three (83) upper limbs were meticulously dissected at the arm, forearm, and cubital fossa to investigate the ABR presence. When the variant muscle was identified, morphometric measurements were obtained.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eThe ABR was identified in two upper limbs (2/83, 2.4%), in a male cadaver, bilaterally. Its origin was located along with the typical BR, and its insertion was identified into the anterior surface of the radius. The radial nerve supplied the ABR, having a course posteriorly to it (in a deeper layer).\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eIn the current study, the variant muscle was observed in 2.4%, while the ABR reported incidence is recorded between 0.5\u0026ndash;2.8%. Radial nerve compression, at the forearm, is not an uncommon entrapment neuropathy. The relationship between the radial nerve and the ABR could precipitate radial neuropathy.\u003c/p\u003e","manuscriptTitle":"The accessory brachioradialis muscle (brachioradialis accessorius): Prevalence of a rare variant with possible implications for radial nerve compression","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-25 09:31:21","doi":"10.21203/rs.3.rs-4675099/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-07-30T11:18:58+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-07-21T08:54:08+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-07-15T17:19:08+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-07-12T20:34:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"322750145042551079126055203495686239698","date":"2024-07-10T15:05:21+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"54210145295450301990724108852507599309","date":"2024-07-08T11:39:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"219808659396654568839275268663741856650","date":"2024-07-04T07:26:23+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-07-03T16:39:48+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-07-03T16:36:36+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-07-03T06:43:23+00:00","index":"","fulltext":""},{"type":"submitted","content":"Surgical and Radiologic Anatomy","date":"2024-07-02T14:47:54+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"surgical-and-radiologic-anatomy","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"sara","sideBox":"Learn more about [Surgical and Radiologic Anatomy](http://link.springer.com/journal/276)","snPcode":"276","submissionUrl":"https://submission.nature.com/new-submission/276/3","title":"Surgical and Radiologic Anatomy","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"146e231a-2181-4ed6-944c-8d94f9938bb1","owner":[],"postedDate":"July 25th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-08-22T19:40:00+00:00","versionOfRecord":{"articleIdentity":"rs-4675099","link":"https://doi.org/10.1007/s00276-024-03462-2","journal":{"identity":"surgical-and-radiologic-anatomy","isVorOnly":false,"title":"Surgical and Radiologic Anatomy"},"publishedOn":"2024-08-13 15:57:38","publishedOnDateReadable":"August 13th, 2024"},"versionCreatedAt":"2024-07-25 09:31:21","video":"","vorDoi":"10.1007/s00276-024-03462-2","vorDoiUrl":"https://doi.org/10.1007/s00276-024-03462-2","workflowStages":[]},"version":"v1","identity":"rs-4675099","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4675099","identity":"rs-4675099","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}