Extensor Indicis Radialis and Extensor Medii Proprius Associated with an Unknown Fibromuscular Slip: a Case Report
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MEDICINE
Extensor Indicis Radialis and Extensor Medii Proprius Associated with an Unknown Fibromuscular Slip: a Case Report Laphatrada Yurasakpong 1 & Rui Diogo 2 & Arada Chaiyamoon 3 & Krai Meemon 1 & Athikhun Suwannakhan 1 Accepted: 23 September 2020 # Springer Nature Switzerland AG 2020
Abstract Posterior compartment of forearm and hand is among the most variable parts of the human body. During a routine dissection, we found two anatomical variants in the right forearm and hand of an 84-year-old male cadaver including the extensor indicis radialis and the extensor medii proprius associated with a fibromuscular slip. Histological analysis using hematoxylin and eosin staining revealed that this unusual fibromuscular slip associated with the extensor medii proprius was composed of dense connective tissue along with small amount of skeletal muscle fibers, and the innervation from the posterior interosseous nerve. Based on the existing literature, a fibromuscular slip associated with a hand extensor tendon on the dorsum of hand has never been reported. Further studies are needed to clarify the evolutionary origin of this structure, although it resembles to a certain extent the dorsometacarpales, a group of muscles that were once present in our mammalian ancestors. Keywords Anatomical variations . Extensor indicis radialis . Extensor medii proprius . Hand . Muscles
Introduction Posterior compartment of forearm and hand is among the most variable parts of the human body. The lack of the understanding of these variations could lead to false diagnosis and inappropriate treatment. A thorough understanding of comparative myology is also critical for developing hypotheses about the functional morphology of modern human musculature. Numerous studies and metaanalyses [1–5] have been conducted to study the anatomy and the prevalence of variations in these regions including the extensor indicis radialis (EIR) muscle, extensor medii proprius (EMP) muscle, extensor indicis et medii communis (EIMC) muscle, extensor pollicis et indicis This article is part of the Topical Collection on Medicine * Athikhun Suwannakhan [email protected] 1
Department of Anatomy, Faculty of Science, Mahidol University, Bangkok, Thailand
2
Department of Anatomy, Howard University College of Medicine, Washington DC, USA
3
Department of Anatomy, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
(EPI) muscle, and extensor digitorum brevis manus (EDBM) muscle. Classification systems were also proposed to systematically identity these variants [1, 6, 7]. According to recent meta-analyses [3, 4], the prevalence of EMP, EIMC, EPI, and EDBM were 3.7%, 1.6%, 0.75%, and 4% respectively. The EIR is an extremely rare variation which existed in only 0.2% of limbs [8]. These variants are believed to be part of the extensor profundus complex, a common digital extensor in the in the deep layer of the posterior forearm muscle group, which variably exists in non-human primate species [9]. Despite the considerable amount of literature s
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