Anatomy of the Foot

Plus, Common Injuries of the Feet and Ankles

artwork of foot anatomy
LEONELLO CALVETTI/Science Photo Library/Getty Images

Your feet are made for walking—and running, jumping, balancing, climbing, and more. So it's no wonder that the human food is complex. Believe it or not, your size sixes (or nines or twelves) house 28 bones—nearly a quarter of all the bones in your entire body—plus 30 joints and more than a hundred muscles, ligaments, and tendons, according to the Arthritis Foundation.

All of these structures work together like fine-tuned machinery to carry out two important functions: weight bearing and propulsion. These functions require a high degree of stability. Also, the foot must be flexible so that it can adapt to uneven surfaces. This is one reason each foot has so many bones and joints.

Here's a brief overview of the structures of the foot and how they work together, plus a look at some common podiatric problems, including Achilles tendonitis, plantar fasciitis, and ankle sprains that sometimes result from normal wear-and-tear, overuse, or injury to the foot.

Foot Structure

The foot can be divided into three sections: the forefoot, midfoot, and hindfoot. Here are the main structures found in each:

Forefoot. This is the very front part of the foot, including the toes, or phalanges. There are 14 toe bones (two per big toe and three per each of the other four), plus five metatarsals. The first metatarsal bone is the shortest and thickest and plays an important role during propulsion (forward movement). It also provides attachment for several tendons. The second, third, and fourth metatarsal bones are the most stable of the metatarsals. They are well-protected and have only minor tendon attachments.

In addition to the phalanges and metatarsals, the forefoot contains two small, oval-shaped sesamoid bones just beneath the head of the first metatarsal, on the plantar surface, or underside, of the foot, that are held in place by tendons and ligaments. The forefoot meets the midfoot at the five tarsometatarsal (TMT) joints.

Midfoot. This section of the foot is made up of five irregularly-shaped bones called the tarsals. The clinical names for these bones are the navicular, cuboid, and medial, intermediate, and lateral cuneiforms. Together they form the arch of the foot, which is key for weight-bearing.

Hindfoot. There are only two large bones in this section of the foot: the talus, and the calcaneus. The largest of these, the calcaneus, forms the heel of the foot. The talus rests on top of the calcaneus and forms the pivoting joint of the ankle.

Foot and Toe Movement

Toe movements take place at the TMT joints. These joints are capable of moving the toes in several directions: plantar flexion (what you do when you point or curl your toes) and dorsiflexion (the clinical term for flexing the toes). In addition, the TMT joints allow the toes to abduct (spread out) and add (squeeze toward each other).

The foot as a whole (excluding the toes) can move in two ways at the ankle joint: It can turn in so that the pinky-toe (outer edge) side of the foot is on the ground and the inner edge of the foot is raised; this is call inversion. The opposite movement, or eversion, is the opposite. All the joints in the hindfoot and midfoot are involved in making these complex movements.

The foot has three arches. The medial longitudinal arch is the highest and most important of the three arches. It is composed of the calcaneus, talus, navicular, cuneiforms, and the first three metatarsals. The lateral longitudinal arch is lower and flatter than the medial arch. It is composed of the calcaneus, cuboid, and the fourth and fifth metatarsals. The transverse arch is composed of the cuneiforms, the cuboid, and the five metatarsal bases.

The arches of the foot are maintained by the shapes of the bones and by the ligaments. Also, muscles and tendons play an important role in supporting the arches.

Muscles of the Foot

The muscles of the foot are classified as intrinsic or extrinsic. The intrinsic muscles, which include the flexors (plantar flexors), extensors (dorsiflexors), abductors, and adductors of the toes, are located within the foot and are responsible for moving the toes. Several intrinsic muscles also help support the arches of the foot.

The extrinsic muscles of the foot are located in the lower leg. They have long tendons that cross the ankle in order to attach to the bones of the foot and assist in movement. The exception is the talus, which has no tendon attachment.) The powerful gastrocnemius (calf) muscle is one of the most important extrinsic foot muscles.

Common Foot Problems

Given how many (literally) moving parts there are in the human foot and how many (literally) thousands of miles this amazing structure logs in a lifetime—according to the American Podiatric Medical Association (APMA), the average person clocks in at 75,000 miles by age 50—it's not surprising that structures within it can be subject to injury or overuse. Here are some of the most common such problems.

Ankle sprains. These are injuries of the ligaments of the ankle in which the ligament becomes overstretched or is partially or totally torn. Ankle sprains typically result from a sudden sideways or twisting movement of the ankle.

Heel pain. Since the heel bone (calcaneus) is the largest bone in the foot, it's especially prone to injury caused by faulty biomechanics (walking in ways that are not optimal), according to the APMA. There are several causes of heel pain. These include heel spurs (bony growths on the underside of the bone); plantar fasciitis (inflammation of the fibrous tissue called fascia that extends from along the sole of the foot from the heel to the ball; and Achilles tendonitis (see below).

Osteoarthritis. This degenerative disease can affect joints in any part of the body. It's caused by progressive damage to cartilage—the connective tissue that provides a layer of padding between bones so that they don't rub against each other. When osteoarthritis affects the feet, it can show up in the ankle joints as well as in the TMT joints that connect the toes to the midfoot. The APMA says that because they take on so much weight over time and contain so many joints, the feet are particularly susceptible to osteoarthritis.

Plantar fasciitis. This condition results from overuse or overstretching of the thick band of connective tissue called the plantar fascia that extends from the heel to the toes along the bottom of the foot. Microtears form in the thick fibrous tissue, causing pain and swelling in the heel, and sometimes bony overgrowths called heel spurs. Plantar fasciitis is a particular risk for long-distance walkers or runners.

Stress fractures. A fracture is a small crack in a bone. In the foot, most such injuries affect the second and third metatarsals, which are located in the part of the foot that takes the most impact during walking and running. Stress fractures also can affect calcaneus (heel) and the navicular bone on the top of the foot.

Tendonitis. This is inflammation of the strong, cord-like tendons in the foot or ankle. Tendonitis usually triggered when a tendon becomes stretched or even torn from overuse. A common type such injury is Achilles tendonitis, which involves the tendon that runs along the back of the heel and is common among people who run or walk a lot whose tendons are tight.