![]() The anterior tibial artery supplies the extensor hallucis longus muscle. Errors in Hox gene expression can lead to malformations in the limbs. These genes control patterning and, consequently, the morphology of the developing limb in the human embryo. SHH activates specific HOX genes – Hoxd-9, Hoxd-10, Hoxd-11, Hoxd-12, Hoxd-13 – which are important in limb polarization and regional specification. SHH is produced by the zone of polarizing activity (ZPA), which promotes the organization of the limb bud along the anterior-posterior axis. The specific fibroblast growth factor involved in hindlimb development is Fgf10, which gets stimulated by Tbx4. The apical ectodermal ridge (AER) produces fibroblast growth factor (Fgf), promoting the outgrowth of the limb buds by stimulating mitosis. Retinoic acid is a global organizing gradient that initiates the production of transcription factors that specify regional differentiation and limb polarization. Several factors influence the formation of the limb bud musculature, including retinoic acid, sonic hedgehog (SHH), HOX genes, apical ectodermal ridge (AER), and the zone of polarizing activity (ZPA). The posterior condensation will develop into the extensor and abductor musculature of the lower limb, and the anterior condensation will form into the flexor and adductor musculature of the lower limb. The embryo's limb buds begin to form about five weeks after fertilization as the mesoderm migrates into the limb bud and forms a posterior condensation and an anterior condensation to eventually form the muscular and skeletal components of the lower limb. Consequently, loss of the extensor hallucis longus can also result in weakness in foot inversion, although typically not clinically significant due to the strong action of the tibialis anterior in inverting the foot. In addition to extending the hallux and dorsiflexing the foot at the ankle, the extensor hallucis longus has a role in weakly inverting the foot due to its insertion on the distal phalanx of the hallux-the most medial toe. Consequently, damage or loss to the muscles or deep peroneal nerve, the innervation of the anterior compartment, can result in foot drop-loss of dorsiflexion-and a characteristic high-stepping gait. ![]() This movement is critical to gait because it allows clearance of the foot off the ground during the swing phase. Due to its origination on the fibula-the lateral bone of the anterior leg-and insertion on the tendon of the distal phalanx of the hallux, muscle contraction lifts the foot and the big toe upward toward the shin (dorsiflexion). The principal function of the extensor hallucis longus is to extend the hallux and dorsiflex the foot at the ankle. The muscle fibers of the extensor hallucis longus course inferiorly and medially, ending in a tendon that passes under the inferior extensor retinaculum, which prevents the muscle from bowstringing or subluxation. The anterior tibial artery and vein and deep peroneal nerve run between the extensor hallucis longus and the tibialis anterior muscles. Its location is between the tibialis anterior and extensor digitorum longus muscles on the anterior side of the lower limb, coursing inferiorly and medially to its insertion point at the base of the distal phalanx of the great toe. The extensor hallucis longus arises from the anterior surface of the fibula and inserts at the base and dorsal center of the distal phalanx of the hallux. ![]()
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