Anatomy Atlases: Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: E: Extensor Pollicis Brevis

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

Extensor Pollicis Brevis

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed

Extensor pollicis brevis, a muscle peculiar to (or individualized to a greater degree in) humans is sometimes absent, being fused with abductor longus, as in the Simiidae. On the other hand, its tendon is often united with that of the long extensor and is inserted with it, or it may be continued as an independent slip to the base of the distal phalanx.

In a study of 118 forearms extensor pollicis brevis inserted onto the first phalanx in 72% of cases, both phalanges in 21%, and the terminal phalanx only, in 6.8%. Extensor pollicis brevis has been reported absent in 6.3% of cases. In another study, the muscle was absent in five of 120 limbs. The muscle may terminate in two tendons, one of which attaches to the base of the first metacarpal.

Macalister has reported the following variations for extensor pollicis brevis:

1. It has been found absent by Wood (1867 and 1868) once in 36 specimens and three times in 36 specimens, this has also been found by S. Moser, and by Macalister;

2. Theile and Henle have seen it fused with abductor pollicis longus as have Wood and Macalister;

3. Its tendon may pass distally to the ungual distal phalanx;

4. The tendon has been described as split (B), and Macalister has found the entire muscle cleft with each part normally attached;

5. Mr. Wood found it replaced by a tendon from the styloid process of the radius to its normal site of insertion;

6. A slip to the tendon of the extensor secundi (extensor pollicis longus) at the base of the ungual phalanx (S);

7. The tendon entirely going to the ungual phalanx;

8. A slip has been seen going to the metacarpal bone at its head; and

9. Or it has been found receiving a slip from the abductor which passed it on to the second phalanx.

Syn.: m. Extensor primi minor, extensor primi internodii pollicis.

References

Bahm, J., Szabo, Z. and G. Foucher (1995) The anatomy of de Quervains's disease. A study of operative findings. Internat. Orthop., 19:209-211.

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

Chopra, R.P., Singh, S. and S.S. Makhni. (1954-56) The insertion of the abductor pollicis longus and extensor pollicis brevis. J. Anat. Soc. India 7:105-109.

Dawson, S. and N. Barton. (1986) Anatomical variations of the extensor pollicis brevis. J. Hand Surg. (B) 11:378-381.

Dubreuil-Chambardel, L. (1919) Des muscles flechisseurs et extenseurs sur un pouce a trois phalanges. Bull. Mem. Soc. Anthropol. Paris. 10:45-47.

Gilles, K.W. (1960) Anatomical variations affecting the surgery of de Quervain's disease. J. Bone Joint Surg. (Br) 42:352-355.

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

Jackson, W.T., Viegas, S.F., Coon, T.M., Stimpson, K.D., Frogameni, A.D. and J.M. Simpson. (1986) Anatomical variations in the first extensor compartment of the wrist. J. Bone Joint Surg. (Am) 68:923-926.

Kaplan, E.B. (1981) Anatomical variations of the forearm and hand. In The Hand, Vol. 1 pp 361-374. R. Tubiana, Ed. W.B. Saunders Company, Philadelphia, 1981.

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.

McGregor, A.L. (1926) A contribution to the morphology of the thumb. J. Anat. 60:266-269.

Stein, A.H. (1951) Variations of the tendons of insertion of the abductor pollicis longus and the extensor pollicis brevis. Anat Rec. 110:49-55.

Tountas, C.P. and R.A. Bergman. (1993) Extensor pollicis brevis. In Anatomic Variations of the Upper Extremity. Churchill Livingstone, New York.

Wood, J. (1864) On some varieties in human myology. Proc. Roy. Soc. Lond. B 13:299-303.

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 16:483-525.

Yoshida, Y. (1990) Anatomical study on the extensor digitorum profundus muscle in the Japanese. Okajimas Folia Anat. Jpn. 66:339-354.

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