Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: E
Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed
Macalister reported the variatins of extensor indicis as follows;
Extensor medii digiti is often a differentiated portion of extensor indicis; arising below that muscle from the back of the ulna, it varies only in its greater or lesser amount of differentiation from its neighbor. Wood found it eleven times in a hundred and two subjects; and the same author has seen it when separate from the extensor indicis, sending an additional tendon to the index finger; in one case this coalesced with the indicator before its insertion. Wood found it arising from the intermuscular septum between the extensor communis digitorum and the supinator brevis (supinator), above the other deep muscles. It has also been seen sending a slip to be inserted partly into the indicator tendon, and partly into the middle metacarpal fascia (Petsche); Meckel found it arising from the radius, Brugnone from the carpus. Most commonly, it is only a second tendon connected with the indicator, and showing no sign of being connected with a separate belly; sometimes, this tendon is an offshoot from the indicator tendon. See below also.
The tendon of extensor indicis is occasionally doubled and one of the slips may pass, although rarely, to the thumb or ring finger, or more commonly to the middle finger. This last slip, forming an extensor digiti III may occur as a separate muscle (2-5%) arising from the ulna, or from the posterior ligament of the wrist joint below the indicator. An extensor digiti IV is a rarer variation. These slips of the deep or short extensor appear to be reversions to a primative arrangement, in which the muscle provides tendons to the whole series of digits. The tendons of these muscles may also be poorly developed.
An extensor digitorum brevis manus is also found in rare cases. Macalister found this muscle once in fifteen subjects while Wood reported once in thirty six subjects. It may appear in two forms: slips arising from the back of the wrist, and slips arising from the carpus or metacarpus may be connected to the tendons of interosseous muscles as well as to the tendons of the extensor.
Extensor digiti medii (present in 10% of bodies) arises from the ulna beneath the extensor indicis, with which it may be fused. It sends a tendon to the extensor aponeurosis of the middle finger or sends slips to the middle finger and the index finger.
Tendinous slips may leave extensor digitorum communis to join those of extensor indicis or extensor pollicis longus. Extensor digitorum brevis (s. extensor brevis digitorum manus), first described by Albinus in 1734, resembles the muscle of the same name on the dorsum of the foot. It may have from one to four fasiculi. The most common fasciculus is one that provides an extensor tendon of the index finger, extensor indicis brevis. This arrangement for the middle finger is nearly as frequent. The fascicle usually arises from the bones of the ulnar half of the carpus (lunate, triquetrum, hamatum, and capitatum) and from the dorsal ligaments joining the bones. The tendons are inserted either into the corresponding extensor tendons or onto the metacarpals. This muscle may be found in about 3 to 9% of bodies. Others have reported frequencies of 2 to 10%. Ogura, et al., found extensor digitorum brevis manus muscle present 28 times in a study of 845 hands; a frequency of 3.3%.
In an extensive study of the extensor indicis proprius muscle, 263 extremities from 140 consecutive cadavers were examined (Cauldwell, et al.). These authors report that in man, the gorilla, and frequently the chimpanzee, a relatively constant special extensor indicis can be found. Inspite of its constancy, the muscle showed marked variation in size origin, insertion, or all of these, in 41 (15.6%) of 263 specimens. In eight specimens (3%) from female cadavers, the muscle was abnormally small. They did not find complete absence although it has been reported.
In three cases (1.4%) the muscle was aberrant at its origin only: 1) a short muscle of carpal origin joined the tendon of a normal indicis; 2) the tendon of an indicis was incorporated with a short muscle of carpal origin; 3) a short muscle arose autonomously from the radial tip and carpus. The short carpal extensor has been termed an "extensor digiti brevis manus."
Complete duplication of the extensor indicis proprius muscle occurred in 5 cases, not counting 5 anomalous short extensor muscles.
Supernumerary tendons, with normal muscle origins, were found in 27 (10.3%) of 263 specimens:
Variations in origin and insertion were observed in 3 cases (1.14%); in one, an anomalous carpal muscle inserting with the middle finger co-existing with a normal indicis proprius; in 2, a short extensor muscle derived tendinous origin from the ulna, muscular origin from the ulna, radius and carpus, and inserted by two tendons with the index and middle fingers - an "extensor digitorum brevis manus." Gama reported a frequency of 1.1% for this muscle in a study of 3004 adults who were randomly examined, 38 were found. Gama also reported that this muscle has been described 128 times between 1743 and1983). reported that extensor digitorum brevis manus (EDBM) was found in 17 of 559 (3%) of dissected hands of 286 cadavers. These were classified into three types, based on their origin. The EDBM insertion was the same as extensor indicis proprius and they were often joined. The two muscles shared the same blood and nerve supply. EDBM was considered a variant and disassociated part of extensor indicis proprius. Excluding variation in origin, supernumerary tendons occurred in 17 (of 135 or 12.6%) right and 13 (of 128 or 10.6%) left extremities, a total of 30 of 263 or 11.4%).
Other studies of "extensor pollicis et indicis" muscle show some variability in frqeuency; Wood reported 1 in 600; Gruber found it in 5% of 204 cadavers, and Wagenseil saw it in 1 of 131 limbs. This muscle is infrequent in humans but is commonly found in the dog, fox, wolf, jackel, panther, and the dingo. It has also been found in the vampire bat, cat, hedgehog, rabbit, bear, coati and beaver. See also Extensor pollicis for illustration.
Extensor pollicis et indicis was described by LeDouble (translation by E. Kaplan in D. T. W. Chiu) as follows: This tendon, which may come off the tendon, or from the muscle of the extensor indicis proprius, or even separately from the epicondyle by muscular or tendinous fibers, may join the tendon of the long extensor of the thumb at the level of the first metacarpal entering the tunnel of extensor pollicis longus at the level of the first metacarpal or into the tunnel for the extensor indicis proprius. This was observed by Monel, Duval, Gruber, Wood, myself ( i.e., LeDouble).
Macalister reported the following variations for extensor indicis;
Extensor medii digiti is often a differentiated part of extensor indicis; arising below extensor indicis from the back of the ulna, it varies only in its greater or less degree of differentiation from its neighbor. Wood found it 11 times in 102 subjects. Wood also found it separate from the extensor indicis, sending an additional tendon to the index finger; in one case the tendon coalesced with the indicator before insertion. Wood has also seen it arising from the intermuscular septum between the extensor communis digitorum and the supinator brevis (supinator), above the other deep muscles. It has also been seen sending a slip to be inserted partly into the indicator tendon, and partly into the middle metacarpal fascia. Meckel found extensor medii digiti arising from the radius and it has been seen arising from the carpus. Most commonly, it is only a second tendon connected with a separate belly; sometimes this tendon is an offshoot from the indicator tendon.
The evolution of the modern name for the special extensor muscle of the index finger is provided by Cauldwell, et al. as follows: Albinus recognized the extensor muscle and noted it in his Historia musculorum hominis (1734). "Vesalius employed the functional designation decimusnonus digitos movetium, and Columbus the topographial term tertius manus exterior musculus. The simplified term indicatorius was introduced by Arantius , and shortened to indicator by Riolan. Strangely enough, the muscle was considered to have an abducting function by Spigelius and Veshing, as witnessed by the respectively given terms indicem abducens and indicis abductor; the thumb is the only reference point that could be used in educing this action, and a more logical one is hard to conceive. Cowper used, extenseur secundi seu indicator. Douglas' ' "nomenclaturic nicety required the unwieldly, extensor secundi internodii indicis proprius, vulgo indicator. The modern usage represents the acceptance, in Latinized form, of Winslow's l'extenseur propre de index."
Syn.: m. Indicator ("vulgar") s. Indicatorius, abductor indicis.
Extensor digiti medii brevis and extensor bicaudatus digiti medii et tertii.from Calori, 1867
Albinus, B.S. (1743) Historia musculorum hominis. Lib. iii, Cap, pp.467-469. Haak & Mulhovium, Leidae, Batavorum.
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Bhadkamkar, A.R. and V.R. Mysorekar. (1960) Bilateral extensor digitorum brevis muscle in the hand. J. Anat. Soc. India. 9:104-105.
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Binns, J.H. (1972) Two cases of extensor digitorum brevis manus. Hand 4:263-264.
Breglia, A. (1886) Di una rara anomalia del plesso brachiale. Rivista Internazionale di Medicina e Chururgia 4:337-344.
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Calori, L. (1867) Di alcune varieta muscolari dell'avambraccio e dell'eminenza ipothenar. Mem. Accad Scienze Istituto di bologna. S, 2. 7:383-393.
Cauldwell, E.W., Anson, B.J., and R.R. Wright. (1943) The extensor indicis proprius muscle. A study of 263 consecutive specimens. Q. Bull. Northwestern Univ. Med. School 17:267-279.
Cheselden, W. (1806) The Anatomy of the Human Body. 2nd American edition. (p.86) David West, Boston.
Chiu, D.T.W. (1981) Supernumerary extensor tendon to the thumb: A report on a rare anatomic variation. Plastic and Reconstructive surg. 68(6):937-939.
Chudzinski, T. (1898) Observations sur les variations musculaire dans les races humaines. Mem. Soc. L'Anthropol. Paris. 2(2):227-?
Compte, -. (1874) Muscles anormaux du dos del main. Lyon Méd.16:161.
Culver, J. (1980) Extensor pollicis and indicis communis tendon: a rare anatomic variation revisited. J. Hand Surg. 5:548-549.
Curnow, J. (1873) Notes of some irregularities in muscles and nerves. J. Anat. Physiol. 7:304-309.
Dunn, A.W. and C.M. Evarts. (1963) The extensor digitorum brevis manus muscle. Clin. Ortho. 28:210-212.
Flower, W.H. and J. Murie. (1867) Account of the dissection of a Bush woman. J. Anat. Physiol. 1:202-208.
Fukuzawa, G. and S. Mitani. (1979) An anomalous extensor digitorum brevis manus. A case report. Clin. Orthop. Surg. 14:1228-1233. In Japanese.
Gahhos, F.N. and S. Ariyan. (1983) Extensor indicis brevis manus: a rare anatomical variation. Ann. Plast. Surg. 10:326-328.
Gama, C. (1983) Extensor digitorum brevis manus: a report of 38 cases, and a review of the literature. J. Hand Surg. 8:575-582.
Gama, C.C. (1976) Musculus extensor digitorum brevis manus. Internat. J. Surg. 61:31-40.
Gebuhr, P. and B. Klareskov. (1987) Extensor digitorum brevis manus. Acta orthop. Scand. 58:85-86.
Glasgow, E.F. (1967) Bilateral extensor digitorum brevis manus. Med. J. Australia 54:24-25.
Gruber, W. (1881) Über den dem constanten Musculus extensor pollicis et indicis gewisser Säugetiere homologen supernumerären Muskel beim Menschen. Arch. Path. Anat. Physiol. Klin. Med. 86:471-491.
Gruber, W. (1882) Über den zum Extensor pollicis et indicis singularis gewordenen extensor pollicis longus beim Menschen. Arch. Path. Anat. Physiol. Klin. Med. 90:103-108.
Gruber, W. (1882) Uber einen zum Extensor indicis et pollicis singularis gewordenen Extensor indicis proprius beim Menschen.- Dasypeus Bildung. Arch. Path. Anat. Physiol. Klin. Med. 95:180-183.
Hart, J.A. L. (1972) Extensor digitorum brevis manus. Hand 4:265-267.
Henle, J. (1871) Handbuch der Muskellehre des Menschen, in Handbuch der systematischen Anatomie des Menschen. Verlag von Friedrich Vieweg und Sohn, Braunschweig.
Jacob, -. (1873) Extenseur propre de l'index envoyant un faiseau au médius. Lyon Med. 13:36.
Jansen, J.H. (1850) Waarnemingen van anomale spieren. Nederlandsch Lancet 1850:431-437.
Jones, B.V. (1959) An anomalous extensor indicis muscle. J. Bone Joint Surg. (B ) 41:763-765.
Kosugi, K., Fujishima, A., Koda, M., and M. Tokudome. (1984) Anatomical study on the variation of the extensor muscles of the forearm. 2. M. extensor digitorum manus brevis. Tokyo Jikekai Med. J. 99:877-883. In Japanese.
Kuczynski, K. (1972) Development of the hand and some anatomical anomalies. Hand 4:1-9.
Kuschner, S.H., Gellman, H.,nd A. Budinger (1989) Extensor digitorum brevis manus. An unusual cause of exercise-induced wrist pain. J. Sports Med. 17:440-441.
Kuwahata, T. and F. Sakamoto. (1959) One case of variation of the M. extensor indicis. Kagoshima Daigaku Igaku Zasshi 11:1440-1442. In Japanese.
LeDouble, A.F. (1897) Traité des variations du Systeme Musculaire de l'Homme et leur Signification au Point de Vue de l'Anthropologie Zoologique. Vol. 2. Schleicher Freres, Paris.
Loup, -. (1875) L'extenseur propre de l'index donne un faisceau au mèdius. Lyon Méd. 18:375.
Lucas, G.L. (1979) An intratendinous cyst in the extensor digitorum brevis manus tendon. J. Hand Surg. 4:176-177.
Lunda, O. and R. Cihak (1967) Clinical significance of muscle extensor digitorum manus brevis and similar variations. Rozhl. Chir. Praha 46:652-658.
Macalister, A. (1875) Additional observations on muscular anomalies in human anatomy (third series) with a catalogue of the principal muscular variations hitherto published. Trans. Roy. Irish Acad. Sci. 25:1-134.
Maguire, W.B. (1977) Les muscles anormaux de la main. Commun. GEM Ann. Chir. 31:371.
Manno, A. (1907) Un cas de M. extensor digitorum brevis de la main. Arch. Ital. Biol. 47:482.
Mercier, -. (1837) Anomalies musculaires. Bulletins et Mem. de la Société Anatomique de Paris XII(11)(1837):321-322.
Moriya, M. (1956) The variation of the M. palmaris longus and the extensor indicis. Tokyo Jikeikai Ikadaigaku Zasshi. 71:2035-2041. In Japanese.
Murakami, Y. and K. Todani. (1982) The extensor indicis brevis muscle with an unusual ganglion. Clin. Orthop. Rel. Res. 162:207-209.
Nomura, S., Torisu, T., and T. Kitajima. (1976) A case of the extensor digitorum brevis manus. Seikei-Geka 27:148-149. In Japanese.
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