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The region of the foot known as the posterior arch includes the area on the underside of the foot that runs from the apex of the arch to the heel. Contained in this part of the foot is the tarsus, a collection of small, irregular bones that link the heel and ankle to the anterior part of the foot. A number of muscles, tendons, and their surrounding fascia contribute to the posterior arch and maintain its shape. The arch is significant for its role in transferring weight toward the front of the foot when the foot strikes the ground.
Actually composed of two longitudinal arches, the medial and lateral antero-posterior arches, the arch of the foot runs from front to back. Its anterior portion consists of the five metatarsal bones, one leading to each toe in the front half of the foot. The first through third metatarsals, those aligned with the big and second two toes, make up the medial anterior arch, while the fourth and fifth metatarsals, those aligned with the two smallest toes, compose the lateral anterior arch.
The metatarsals meet the tarsal bones at the highest point of these arches, which is where the posterior arch begins. The tarsus consists of the calcaneus, talus, navicular, cuboid, and three cuneiform bones, with the calcaneus also known as the heel bone and the talus situated on top of the heel bone below the ankle. Linking the heel to the midfoot are the remaining five bones: the navicular on the medial or big-toe side of the foot, the cuboid on the lateral or little-toe side of the foot, and the first through third cuboid bones on the medial side in front of the navicular. Included in the medial posterior arch are the talus, calcaneus, navicular, and three cuneiform bones, while in the lateral posterior arch are the outside portion of the calcaneus and the cuboid.
Running through the posterior arch beneath and among these bones are multiple soft tissues that lend both support and elasticity to the arch. Among the most significant of these are the plantar calcaneonavicular ligament, the plantar aponeurosis, and the tendon of the tibialis posterior muscles. The plantar calcaneonavicular ligament is a thick band of fibrous tissue that crosses the posterior arch, linking the front of the calcaneus bone to the navicular. It is also known as the spring ligament for the elasticity it lends to the arch.
Similarly, the plantar aponeurosis or plantar fascia is a soft tissue of the posterior arch that crosses from the heel bone to the metatarsals and helps support the arch as well as transfer forces toward the ball of the foot. Plantar fasciitis is a common and well-known condition in which this tissue becomes painfully inflamed. The posterior arch is also supported and stabilized by the branches of the tendon of the tibialis posterior, a deep muscle of the calf. This tendon divides into multiple segments in the hindfoot that affix to the calcaneus, navicular, cuboid, and all three cuneiforms in the posterior arch as well as the middle three metatarsals in the anterior arch.