DEEP FASCIA OF FOOT
The deep fascia of the dorsum of the foot is thin where it is continuous proximally with the inferior extensor retinaculum. Over the lateral and posterior aspects of the foot, the deep fascia is continuous with the plantar fascia, the deep fascia of the sole. The plantar fascia has a thick central part and weaker medial and lateral parts.
The thick, central part of the plantar fascia forms the strong plantar aponeurosis , longitudinally arranged bundles of dense fibrous connective tissue investing the central plantar muscles. It resembles the palmar aponeurosis of the palm of the hand but is tougher, denser, and elongated.
The plantar fascia holds the parts of the foot together, helps protect the sole from injury, and helps to support the longitudinal arches of the foot.
The plantar aponeurosis arises posteriorly from the calcaneus and functions like a superficial ligament. Distally, the longitudinal bundles of collagen fibers of the aponeurosis divide into five bands that become continuous with the fibrous digital sheaths that enclose the flexor tendons that pass to the toes. At the anterior end of the sole, inferior to the heads of the metatarsals, the aponeurosis is reinforced by transverse fibers forming the superficial transverse metatarsal ligament .
In the midfoot and forefoot, vertical intermuscular septa extend deeply (superiorly) from the margins of the plantar aponeurosis toward the 1st and 5th metatarsals, forming the three compartments of the sole:
The medial compartment of the sole is covered superficially by thinner medial plantar fascia . It contains the abductor hallucis, flexor hallucis brevis, the tendon of the flexor hallucis longus, and the medial plantar nerve and vessels.
The central compartment of the sole is covered superficially by the dense plantar aponeurosis . It contains the flexor digitorum brevis; the tendons of the flexor hallucis longus and flexor digitorum longus, plus the muscles associated with the latter; the quadratus plantae and lumbricals, and the adductor hallucis. The lateral plantar nerve and vessels are also located here.
The lateral compartment of the sole is covered superficially by the thinner lateral plantar fascia and contains the abductor and flexor digiti minimi brevis.
In the forefoot only, a fourth compartment, the interosseous compartment of the foot , is surrounded by the plantar and dorsal interosseous fascias. It contains the metatarsals, the dorsal and plantar interosseous muscles, and the deep plantar and metatarsal vessels. Whereas the plantar interossei and plantar metatarsal vessels are distinctly plantar in position, the remaining structures of the compartment are located intermediate between the plantar and dorsal aspects of the foot.
A fifth compartment, the dorsal compartment of the foot , lies between the dorsal fascia of the foot and the tarsal bones and the dorsal interosseous fascia of the midfoot and forefoot. It contains the muscles (extensors hallucis brevis and extensor digitorum brevis) and neurovascular structures of the dorsum of the foot.