The structure of the extensor pollicis et indicis communis resembles both the characteristics of the extensor pollicis longus and the extensor indicis proprius. It originates from the distal end of ulna. Its tendon passes through the extensor retinaculum in the fourth extensor compartment, splits into two and inserts to both thumb and index finger. The presence of the extensor pollicis et indicis communis, on the other hand, may impair thumb adduction.[3]
It was reported as an unusual juncturae tendinum, a tendinous connection between tendon of the extensor pollicis longus and tendon of the extensor digitorum communis to the index finger.[4] It was also identified as a slip of the extensor indicis proprius to the extensor pollicis longus in an Indian cadaver.[5]
In other animals
In many species of New World monkeys, a muscle similar to the extensor pollicis et indicis communis was found to be a normal anatomy rather than an anatomical variation.[6] It is described as the extensor pollicis et indicis longus.[6] In chimpanzees and humans, however, the muscle is well separated becoming the extensor pollicis longus and the extensor indicis proprius.[7]
^Martínez, Daniel Casanova; Gandur, Iván Valdivia; Golanó, Pau (2012-12-20). "Extensor pollicis et indicis communis or extensor indicis radialis muscle". Anatomical Science International. 88 (3): 153–155. doi:10.1007/s12565-012-0164-8. ISSN1447-6959. PMID23255266.
^Komiyama, M.; Nwe, T. M.; Toyota, N.; Shimada, Y. (1999-10-01). "Variations of the extensor indicis muscle and tendon". Journal of Hand Surgery (Edinburgh, Scotland). 24 (5): 575–578. doi:10.1054/jhsb.1999.0239. ISSN0266-7681. PMID10597935.
^Steichen, J. B.; Petersen, D. P. (1984-09-01). "Junctura tendinum between extensor digitorum communis and extensor pollicis longus". The Journal of Hand Surgery. 9 (5): 674–676. doi:10.1016/s0363-5023(84)80011-8. ISSN0363-5023. PMID6491210.
^Bolwar, Preeti R. (2011). "A study of anatomical variations of the extensor tendons of the index finger and their significance". Eur J Anat. 15: 129–135.
^Aversi-Ferreira, T. A.; Diogo, R.; Potau, J. M.; Bello, G.; Pastor, J. F.; Aziz, M. Ashraf (2010-12-01). "Comparative anatomical study of the forearm extensor muscles of Cebus libidinosus (Rylands et al., 2000; Primates, Cebidae), modern humans, and other primates, with comments on primate evolution, phylogeny, and manipulatory behavior". Anatomical Record. 293 (12): 2056–2070. doi:10.1002/ar.21275. ISSN1932-8494. PMID21082733.