Anatomy

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Overview

The human foot combines mechanical complexity and structural strength. The ankle serves as foundation, shock absorber, and propulsion engine. The foot can sustain enormous pressure (several tons over the course of a one-mile run) and provides flexibility and resiliency.

The foot and ankle contain:

• 26 bones (One-quarter of the bones in the human body are in the feet.);
  
• 33 joints;
  
• more than 100 muscles, tendons (fibrous tissues that connect muscles to bones), and ligaments (fibrous tissues that connect bones to other bones); and
  
• a network of blood vessels, nerves, skin, and soft tissue.

These components work together 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. Abnormalities in other parts of the body can lead to problems in the feet.

Parts of the Foot
Structurally, the foot has three main parts: the forefoot, the midfoot, and the hindfoot.

Top View of Foot Bones	Side View of Foot Bones
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The forefoot is composed of the five toes (called phalanges) and their connecting long bones (metatarsals). Each toe (phalanx) is made up of several small bones. The big toe (also known as the hallux) has two phalanx bones—distal and proximal. It has one joint, called the interphalangeal joint. The big toe articulates with the head of the first metatarsal and is called the first metatarsophalangeal joint (MTPJ for short). Underneath the first metatarsal head are two tiny, round bones called sesamoids. 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. The forefoot bears half the body's weight and balances pressure on the ball of the foot.

The midfoot has five irregularly shaped tarsal bones, forms the foot's arch, and serves as a shock absorber. The bones of the midfoot are connected to the forefoot and the hindfoot by muscles and the plantar fascia (arch ligament).

The hindfoot is composed of three joints and links the midfoot to the ankle (talus). The top of the talus is connected to the two long bones of the lower leg (tibia and fibula), forming a hinge that allows the foot to move up and down. The heel bone (calcaneus) is the largest bone in the foot. It joins the talus to form the subtalar joint. The bottom of the heel bone is cushioned by a layer of fat.

Musles, Tendons, and Ligaments
A network of muscles, tendons, and ligaments supports the bones and joints in the foot.

Front View of Foot Muscles	Side View of Foot Muscles	Back View of Foot Muscles
Click on the images to view a larger version.

There are 20 muscles in the foot that give the foot its shape by holding the bones in position and expand and contract to impart movement. 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 to initiate the act of stepping forward; and
• the flexors, which help stabilize the toes against the ground.

Smaller muscles enable the toes to lift and curl.

There are elastic tissues (tendons) in the foot 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 to the heel. Its strength and joint function facilitate running, jumping, walking up stairs, and 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 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 give the foot its shape and durability, provide cell regeneration and essential muscular nourishment, and control its varied movements.

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