The plantar fascia is a strong connective tissue structure that runs almost the full length of the plantar aspect of the foot from its origin at the os calcis to its complex insertion at the level of the heads of the metatarsals. It is the most important of several ligamentous bands that maintain the longitudinal arch of the foot. The other ligaments include the short and long plantar ligaments.The short plantar ligament runs from a more distal point on the undersurface of the os calcis to insert into the undersurface of the navicular. The long plantar ligament also arises from the os calcis and inserts on the bases of the second to fifth metatarsals. The long plantar ligament is separated from the plantar fascia by several layers of muscles and tendons. The deepest of these is quadratus plantae, which inserts onto flexor hallucis longus.Superficial to this are the bellies of three important muscles. Centrally is flexor digitorum brevis and then on either side are abductor digiti minimi laterally and abductor hallucis medially (Fig. 1). The plantar fascia overlies these muscles. Also called the plantar aponeurosis, the plantar fascia comprises three bundles: central, lateral, and medial. The medial bundle is the least significant of these and arises from the midportion of the central bundle extending over abductor hallucis to combine with the deep fascia on the medial aspect of the foot. Some previous descriptions have not recognized this structure but identify only two bundles. Under this terminology, the central bundle is referred to as the medial bundle; this should not be confused with the true medial bundle. For the remainder of this article, the three-bundle terminology is used.
The central bundle is the most important of the three bundles and the one most commonly affected by disease. It runs from the medial tubercle of the os calcis distally and divides into five limbs, each of which blends with the deep fascia and transverse ligaments that themselves combine at the level of the heads of the metatarsals. The lateral bundle lies beneath the abductor digiti minimi. Two branches of the posterior tibial nerve innervate the fascia. The most superficial of these, the medial calcaneal nerve, arises directly from the posterior tibial nerve. The deeper, more important branch is called the first branch of the lateral plantar nerve, which, as the name implies, arises from the lateral plantar nerve.The lateral plantar nerve is the first substantial division of the posterior tibial nerve.