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Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: E

Extensor Digitorum Communis

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD

Peer Review Status: Internally Peer Reviewed

Variations of extensor digitorum communis include the occasional deficiency of one or more tendons of insertion or an increase in their number to five, supplying the five digits. If one of the tendons is absent it is usually that to the fifth digit. More frequently, however, the tendons are limited to the index or middle finger alone, although an additional slip to the thumb is occasionally seen. Any digit may receive two tendons.

Wood reported a hand with tendons doubled to the second, third and fifth fingers. The fleshy part of the muscle may consist of two to four bellies, one for each tendon of insertion. Tendinous slips may leave the muscle and join those of extensor Indicis or extensor pollicis longus. The head to the second finger was found arising from extensor carpi radialis brevis, and another head supplied the third finger (Henle).

Mori provides statistical data on the condition of the terminal tendon of extensor digitorum as follows:

The tendon for the third digit is doubled in 2.5%.
The tendon for the fourth digit is doubled in 5.0%.
The tendon for the fifth digit is doubled in 12.5%.
The tendons of the second and fourth digits are doubled in 2.5%.
The tendons of the fourth and fifth digits are doubled in 2.5%.
The tendons of the third, fourth, and fifth digits are doubled in 15%.
The tendons of the third and fifth digits are doubled in 2.5% of Mori's cases.

The absence of junctura tendinea:
The junctura tendinae may be absent between the index and middle fingers, 10.0%; may be absent between the ring and little fingers, 2.5%; may be absent between the middle and ring fingers 10%. The terminal tendon for the little finger may be absent in 4% of subjects.

Macalister observations complement those of Mori as follows: Extensor communis digitorum:

1. The little finger tendon may be absent;
2. The tendon for each finger may be doubled;
3. Partial doubling of the ring finger tendon;
4. Exclusive doubling of the index tendon;
5. Tendon for the middle-finger only doubled.
6. Tendon for the middle-finger trebled;
7. With the middle and ring doubled, the contigous portions being joined by a vinculum;
8. The index tendon being doubled, and the ulnar (side) tendon being joined to the middle finger tendon;
9. All tendons united by vincula;
10. Mr. Wood described the occurrence of this, one of the index tendons being the only one free;
11. Albinus reported a separate belly for each tendon, and the same has been reported by Brugnone, Meckel, and by Wood;
12. A special (accessory) belly for the index finger tendon has been reported by Henle, Wood and Macalister;
13. the little finger tendon may be doubled;
14. the ring and little finger tendons both doubled;
15. The index and little finger tendons both doubled;
16. Wood reported, in one case, two tendons to the index and little fingers, and four to the ring finger;
17. This muscle may send a slip in the groove with the extensor secundi internodii pollicis (extensor pollicis longus), which it joined at the base of the first phalanx of the thumb (Macalister and by Wood);
18. Mr. Wood saw a similar slip going to the indicator (first finger);
19. Extensor digitorum communis (edc) may send one, two, or three slips to substitute the extensor digiti minimi, when this muscle was absent;
20. It has been found likewise deficient of a tendon for the second finger, the tendon for which arose from extensor carpi radialis brevis;
21. It can be seen with two bellies, one supplying the second and third, and one to the fourth and fifth;
22. The third and fourth bellies may be split into two parts, each of which had a tendon inserted into their respective fingers;
23. Sömmerring saw it send a slip that joined extensor digiti minimi; and
24. Rüdinger had a case where there was a remarkable subdivision of the extensor muscles, in which there were eleven extensor tendons for the fingers between this muscle, the extensores medii et tertii digiti, and the indicator. See also Extensor indicis.

Image 41

Extensor Digitorum Communis Supplying Index, Middle, and Ring Fingers as a single unit.
from Vesalius, Fabricus, 1543, in Straus, Jr. and Temkin.

Image 45

Extensor Medii Proprius.
from Vesalius, Fabricus, 1543, in Straus, Jr. and Temkin.

Image 19

Doubled Extensor Digiti Medii.
from Calori.

Image 16

Extensor digiti medii longus and brevis.
from Calori


Bankart, J., Pye-Smith, P.H., and J.J. Phillips. (1869) Note of abnormalities observed in the dissection room during sessions of 1866-7, 1867-68. Guy's Hospital Report. 14:436-455.

Baumann, J.A. (1947) Valeur, variation, et équivalences des muscles extenseurs, interosseux, adducteurs de la main et du pied chez l'homme. 4:10-16.

Calori, L. (1867) Di alcune varieta muscolari dell'avambraccio e dell'eminenza ipothenar. Mem. Accad Scienze Istituto di Bologna. S. 2. VII:383-393.

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.

Clason, E. (1869) Om muskelanomalier. Upsala Läkareforening Förhandlingar. IV:244-248.

Cogniard, -. (1874) Fasciculation des muscles extenseurs des doigts. Lyon Med. 15:500.

Culver, J. (1980) Extensor pollicis and Indicis communis tendon: a rare anatomic variation revisited. J. Hand Surg. 5:548-549.

Ebisawa, K. (1954) The tendons of the extensors of the fingers. Kaibogaku Zasshi. 29:164. In Japanese.

Ebisawa, K. (1960) The form of the tendons of the extensors on the dorsum of the hand. Nihon Ikadaigaku Zasshi. 19:831-846. In Japanese.

Egawa, T. and K. Hashimoto. (1966) An anomalous extensor Indicis muscle - A case report. Bull. NY Hosp. Joint Dis. 27:116-119.

Gantzer, C.F.L. (1813) Extensor digitorum Varietät. Thesis. J.F. Starkii, Berolini.

Gruber, W. (1875) Über den Musculus extensor digitorum communis manus anomalous mit 5 Sehnen zu allen Fingern, und über den Musculus extensor digitorum longus pedis anomalous mit 5 Sehnen zu allen Zehen. Arch. Anat. Physiol. Wissen. Med. 1875:204-210.

Gruber, W. (1878) Musculus extensor digitorum communis manus anomalous mit 5 Sehnen zu allen Fingern. Arch. Path. Anat. Physiol. Klin. Med. 72:500-501. Gruber, W. (1879) Nachtrag zum Vorkommen des Musculus extensor digitorum communis manus mit 5 Sehnen zu allen Fingern. Arch. Path. Anat. Physiol. Klin. Med. 77:129-130.

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 einen anomalen, den constanten Musculus extensor digitorum communis manus zu allen 5 Fingern bei den Säugetieren Genera Myogale und Fiber Homologen Muskel beim Menschen. Arch. Path. Anat. Physiol. Klin. Med. 90:88-97.

Gruber, W. (1882) Über anomale, dem constanten Musculus extensor digitorum communis manus zum 2.-4. Fingern bei Asplax und Dasypus, und dem constanten Musculus extensor digitorum communis manus zum 1.-4. Fingern bei Echidna homologe Muskeln beim Menschen. Arch. Path. Anat. Physiol. Klin. Med. 90:97-103.

Gruber, W. (1882) Über einen zum Extensor indicis et pollicis singularis gewordenen Extensor indicis proprius beim Menschen - Dasypeus Bildung. Arch. Path. Anat. Physiol. Klin. Med. 90:108-110.

Gruber, W. (1885) Düplicität des Musculus extensor digiti quinti et quarti proprius manus. Arch. Path. Anat. Physiol. Klin. Med. 101:260-262.

Gruber, W. (1887) Seltener Extensor proprius digiti quinti manus bei dem Menschen und bei den Menschen und bei Säugethieren. Arch. Pathol. Anat. Physiol. Klin. Med. 107:478-480.

Gruber, W. (1888) Vagina propria im ligamentum carpi dorsale fur den Bäuch des Extensor digitorum communis manus zum Zeigefingern beim Menschen - und dieselbe analoge Vagina fur den Bäuch desselben Muskels fur die 2. Zehe des Vorderfusses bei Phascolarctos cinereus. Arch. Path. Anat. Physiol. Klin. Med. 114:369-371.

Henle, J. (1871) Handbuch der Muskellehre des Menschen., in Handbuch der systematischen Anatomie des Menschen. Verlag von Friedrich Vieweg und Sohn, Braunschweig.

Ishizuki, M., Furyua, K., and T. Kumakura. (1986) Extensor digitorum brevis manus associated with attrition rupture of a common extensor tendon. J. Hand Surg. (A): 11(4):582-584.

Jones, B.V. and I. Suffolk (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 Jikeikai Med. J. 99:877-883. In Japanese.

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.

Mori, M. (1966) Statistics on the musculature of the Japanese. Okajimas Fol. Anat. Jap. 40:195-300.

Scheldrup, E.W. (1951) Tendon sheath patterns in the hand: an anatomical study based on 367 hand dissections. Surg., Gynecol. Obstet. 93:16-22.

Schenk, R.R. (1964) Variations of the extensor tendons of the fingers. Surgical significance. J. Bone Joint Surg. (A) 46:103-110.

von Schroeder, H.P., Botte, M.J., and H. Gellman. (1990) Anatomy of the juncturae tendinum of the hand. J. Hand Surg. 15A:595-602.

Spinner, M. and K. Olshansky. (1973) The extensor indicis proprius syndrome - A clinical test. Plast. Reconstr. Surg. 51:134-138.

Steichen, J.B. and D.P. Peterson. (1984) Junctura tendinum between extensor digitorum communis and extensor pollicis longus. J. Hand Surg. (A) 9:674-676.

Straus, Jr.,W.L. (1941) Phyologeny of the human forearm extensors. Hum. Biol. 13:203-238.

Straus, Jr., W.L. and O. Temkin. (1943) Vesalius and the problem of variability. Bull. Hist. Med. 14:609-633.

Sunderland, S. (1945) The actions of the extensor digitorum communis, interosseous and lumbrical muscles. Am. J. Anat. 77:189-209.

Testut, L. (1884) Les Anomalies Musculaires Chez l'Homme Expliquees par L'Anatomie Comparee. Masson, Paris.

Vesalius, A. (1555) De Humani Corporis Fabrica. Oporinum, Basle.

de Vilhena, H. (1933) Le muscle surnuméraire extenseur commun du pouce et de l'index. Assoc. Anat., Comptes Rendus 26:685-702

Wood, J. (1868) Variations in human myology observed during the winter session of 1867-68 at King's College, London. Proc. Roy. Soc. Lond. B 17:483-525.

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