A marvel of bioengineering, the human foot combines the mechanical complexity of a Swiss watch with the structural strength of a cantilever bridge. The ankle, it serves as foundation, shock absorber and propulsion engine. The foot can sustain enormous pressure - several tons over the course of a one-mile run, for example - and still provide the combination of flexibility and resiliency needed to support delicate and demanding ballet steps.
The foot and ankle contain: 26 bones; 33 joints; more than 100 muscles, tendons (fibrous tissues that connect muscles to bones) and ligaments (fibrous tissues connecting bones to other bones); and a vast network of blood vessels, nerves, skin and soft tissue. Together, the feet contain one-quarter of the bones in the human body. All of these components work together in unison to provide the body with support, balance and mobility. A structural flaw or malfunction in any one part can result in the development of problems elsewhere in the body. Conversely, abnormalities in other parts of the body ultimately can lead to problems in the feet.
Parts of the Foot Structurally, the foot has three main parts; the forefoot, the midfoot, and the rearfoot.
The forefoot is composed of the five toes, collectively called phalanges, and their connecting long bones, the metatarsals. Each toe, or phalanx, is made up of several small bones. The big toe, also called the hallux, has two phalanges and one joint (interphalangeal joint); it also features two tiny, round sesamoid bones that enable it to move up and down. The other four toes each have three bones and two joints. The phalanges are connected to the metatarsals by five metatarsal phalangeal joints at the ball of the foot. Collectively, the forefoot bears half the body's weight and balances pressure on the ball of the foot.
The midfoot, featuring five irregularly shaped tarsal bones, forms the foot's characteristic arch and serves as a shock absorber. The bones of the midfoot are connected to the forefoot and the rearfoot by muscles and the plantar fascia or arch ligament.
The rearfoot, composed of three joints, links the midfoot to the ankle or talus. The top of the talus is connected to the two long bones of the lower leg, the tibia and fibula, forming a hinge that allows the foot to move up and down. The heel bone or calcaneus, is the largest bone of the foot. It joins the talus to form the subtalar joint, which enables the foot to rotate at the ankle. Its bottom is cushioned with a layer of fat.
Supporting this complex of bones and joints is a network of muscles, tendons, and ligaments. There are some 20 muscles in the foot. They give the foot its shape by holding the bones in position, and expand and contract to impart movement to the bones and joints. The main muscles of the foot are:
the anterior tibial, which enables the foot to move upward;
the posterior tibial, which supports the arch;
the peroneal tibial, which controls movement on the outside of the ankle;
the extensors, which help the ankle raise the toes and initiate the act of stepping forward;
and the flexors, which help stabilize the toes against the ground.
Other smaller muscles enable the toes to lift and curl. In the foot there are elastic tissues that connect the muscles to the bones and joints. The largest and strongest tendon of the foot is the Achilles tendon, which extends from the calf muscle of the leg to the heel. Its strength and joint function facilitate running, jumping, walking up stairs or raising the body onto the toes.
Ligaments hold the tendons in place and stabilize the joints. The longest of these, the plantar fascia, forms the arch on the sole of the foot from the heel to the toes. By stretching and contracting, it allows the arch to curve or flatten, providing balance and giving the foot strength to push off and initiate the act of walking. Medial ligaments on the inside and lateral ligaments on outside of the foot provide stability and enable the foot to move up and down.
Skin, blood vessels and nerves help give the foot its shape and durability, provide cell regeneration and essential muscular nourishment, and control its many, varied movements.