Extensor Hallucis Longus

This muscle is occasionally united at its origin with extensor digitorum longus. The tendon may be divided into three slips confined to the great toe; a slip to the second toe has also been observed.

Macalister found the following variations for this muscle: 1. The muscle may be doubled (Meckel, Henle); 2. It may have a common muscular slip between it and extensor digitorum; 3. With a slip to the extensor hallucis brevis at the junction of its muscle and tendon; 4. It may be joined to extensor ossis metatarsi hallucis.

Extensor ossis metatarsi hallucis may exist as a slip of the last, or with a distinct belly arising beside the usual extensor, or with a tendon from the annular ligament, and no belly; or, as an offshoot from the tibialis anticus (anterior), or extensor digitorum longus. When separate, it traverses the same groove in the annular ligament as the extensor hallucis.

Occasionally this muscle, which is usually unipennate, has three bellies and three tendons and is named extensor hallucis longus tricaudatus (Gruber). When one of these three bellies is represented as a separate (and usually smaller) muscle, it is named extensor hallucis longus minor.

Doubling of the muscle may occur anywhere along its length with the extra muscle (extensor primi internodii hallucis longus [Wood]) running parallel and lateral to the main muscle. It may be joined to the tendon of extensor hallucis brevis distally or insert independently onto the first metatarsal, the proximal part of the first phalanx, or both phalanges of the great toe. Rarely it arises below the usual extensor, or it may arise from the tendon of the extensor at the ankle, or three inches (inch = 2.54 cm) above it. Wood found it as a tendinous offshoot from extensor digitorum longus; its insertion may be separate from extensor brevis. Wood found it present in nearly one-half of the subjects examined by him.

Reference Gruber, W. (1875) Über die varietäten des Musculus extensor hallucis longus. Arch. Anat. Physiol. Wissen. Med. 1875:565-589.

Gruber, W. (1876) Ein neuer Fall von Musculus extensor hallucis longus tricaudatus. Arch. Anat. Physiol. Wissen. Med. 1876:750-752.

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

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.

Natsis, K., Konstantinidis, G.A., Symeonidis, P.D. et al. The accessory tendon of extensor hallucis longus muscle and its correlation to hallux valgus deformity: a cadaveric study. Surg Radiol Anat (2017). https://doi.org/10.1007/s00276-017-1881-4

Perret, M. et M. Trossat. (1876) Anomalie de l'extenseur propre du gros orteil. Lyon Méd. 22:123.