Morphological variability of the extensor hallucis longus in human fetuses.

The extensor hallucis longus originates from about the middle three fifths of the anterior surface of the fibula, medial to the origin of the extensor digitorum longus, and inserts into the distal phalanx of the great toe. The goal of this study was to examine the insertion of the extensor hallucis longus tendon and thus prepare its first classification in human fetuses. Fifty spontaneously-aborted human fetuses (26 male, 24 female, 100 lower limbs), aged 18-38 weeks of gestation, were examined. The classification comprised three types of extensor hallucis longus insertion. The most common was type I (68%), which was characterized by a single tendon that ends as an extensor hood inserting into the dorsal aspect of the base of the distal phalanx of the great toe. The second most frequent was type II (27%), which was characterized by two distal tendons: the dominant one ends as an extensor hood inserting into the distal phalanx of the great toe, and the auxiliary inserts separately into the dorsal aspect of the proximal phalanx of the great toe, medial to the insertion of the extensor hallucis brevis tendon. Finally, type III (5%), the least frequent type, was characterized by two distal tendons: the dominant one ends as an extensor hood inserting into the distal phalanx of the great toe, and the auxiliary connects to the tendon of the extensor hallucis brevis. The extensor hallucis longus demonstrates great variability in the approach of its tendon to the foot, at least in fetuses, as indicated by this initial classification.

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