Found in the back of the lower limb, the posterior tibial artery begins behind the knee and descends the leg toward the back of the foot. It is a branch of the popliteal artery and itself splits into the medial and lateral plantar arteries in the foot as well as forms a branch just below the knee called the fibular or peroneal artery. Arteries carry oxygen-rich blood away from the heart, so the direction of blood flow in the posterior tibial artery is downward. This vessel is attended by the posterior tibial vein, which lies to the inside of the artery and transports blood back up the leg.
As a branch of the popliteal artery, the posterior tibial artery receives blood from this larger vessel, as does its other branch, the anterior tibial artery, which supplies the front of the lower leg. The popliteal artery divides into these two vessels at the height of the bottommost edge of the popliteus, a muscle that crosses the back of the knee. A short distance below this point near the top of the calf, the posterior artery gives off its own branch, the peroneal artery, which angles toward the outside of the posterior leg behind the fibula bone.
From here, the posterior tibial artery descends the limb behind the tibia bone, gradually curving toward the inside of the ankle. It crosses the joint behind the medial malleolus of the tibia, the bulged portion of the bottom of the bone visible along the inside of the ankle. The vessel lies between the malleolus and the Achilles tendon. In fact, a pulse from the artery can be felt here. Along with the tendons of the tibialis posterior, flexor digitorum longus, and flexor hallucis longus muscles, as well as the posterior tibial vein and the tibial nerve, the artery is bundled behind the ankle by the flexor retinaculum, a horizontal band of ligament.
After passing behind the ankle, the posterior tibial artery divides into two smaller arteries of the plantar surface or underside of the foot: the medial and lateral plantar arteries. This occurs beneath the calcaneus or heel bone, with the medial plantar artery directing toward the big toe and the lateral plantar artery supplying the four smaller toes. Just as the posterior tibial artery brings oxygen-and-nutrient-dense blood to the muscles and tissues of the posterior lower leg, the plantar arteries supply those of the sole of the foot.