The axis artery then gives off branches that form the anterior tibial artery and the posterior tibial artery. The earliest arterial supply of the lower limb bud is the axis artery and the terminal plexus, both of which come from the umbilical artery. SHH activates specific HOX genes – Hoxd-9, Hoxd-10, Hoxd-11, Hoxd-12, Hoxd-13 – which are essential in limb polarization and regional specification. The zone of polarizing activity (ZPA) manufactures SHH, which promotes the organization of the limb bud along the anterior-posterior axis. The apical ectodermal ridge (AER) produces fibroblast growth factor (FGF), which promotes 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 vasculature and musculature, including retinoic acid, sonic hedgehog (SHH), HOX genes, apical ectodermal ridge (AER) and the zone of polarizing activity (ZPA). The limb buds of the embryo begin to form about five weeks after fertilization as the lateral plate mesoderm migrates into the limb bud region and condenses along the central axis to eventually form the vasculature and skeletal components of the lower limb. In the foot, the posterior tibial artery bifurcates into the medial and lateral plantar arteries after crossing the sustentaculum tali. It then gives off the distinct branches of the posterior medial malleolar artery and the artery of the tarsal canal, which is the dominant blood supply to the talar body. At the level of the ankle, its path is more superficial, and it is palpable posterior to the medial malleolus as it courses through the tarsal tunnel. It travels with the tibial nerve in the deep posterior compartment of the leg along its fascial border with the superficial compartment. The posterior tibial artery is the largest of the terminal branches of the popliteal artery. The tibioperoneal trunk then divides approximately 2.5 cm from its origin, into the peroneal and posterior tibial arteries. The popliteal artery divides toward the distal end of the popliteal fossa to give rise to the tibioperoneal trunk and the anterior tibial artery. The superficial femoral artery continues inferiorly passing through the adductor hiatus into the popliteal fossa to become the popliteal artery posterior to the knee. The deep branch (profunda femoris artery) continues to supply the posterior structures of the thigh through the medial circumflex femoral artery and lateral circumflex femoral artery. The blood supply of each of the four compartments of the lower limb originates at the common femoral artery, a branch of the external iliac artery, which eventually splits into deep and superficial branches. There have been only 33 documented cases of true infra-popliteal arterial aneurysms, twelve of which involve the posterior tibial artery. The arteries of the lower limb are susceptible to several pathologies, including atherosclerotic plaque buildup, compartment syndrome, trauma, and in rare instances, aneurysm. The posterior compartment muscles serve as the primary flexors of the ankle (plantarflexion) and flexors of the toes. The superficial and deep posterior compartment muscles are supplied by the posterior tibial artery and innervated by the tibial nerve, both of which course in the deep posterior compartment. The deep posterior compartment contains the tibialis posterior, flexor digitorum longus, and flexor hallucis longus muscles. The superficial posterior compartment contains the gastrocnemius, soleus, and plantaris muscles. The lateral compartment muscles function primarily to evert the foot and weakly plantarflex the foot at the ankle. The peroneal artery provides muscular branches to the lateral compartment but is, in fact, a posterior compartment structure. The lateral compartment of the lower limb contains the fibularis longus and brevis muscles and receive innervation from the superficial fibular nerve. The anterior compartment muscles function as the primary extensors of the ankle (dorsiflexion) and extensors of the toes. The anterior compartment contains the tibialis anterior, extensor hallucis longus, extensor digitorum longus, and fibularis tertius muscles, innervated by the deep peroneal nerve and supplied by the anterior tibial artery. These four compartments are the anterior, lateral, superficial posterior, and deep posterior compartments. The lower leg divides into four compartments.
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