Medical trivia question: What is the most uniquely human part of the body? The answer, which may come as a surprise, is the foot! No other part of our bodies can make such a claim.

The uniquely human foot is a masterpiece of engineering that, though often taken for granted or neglected, is the foundation of our whole body.

Because we walk on two feet instead of four, the shapes and positions of the 26 bones in each foot are designed far differently than those in any other species of animal.

The unique anatomy and bio-mechanics of our lower extremities explains many of the medical conditions of the foot.

Bones
The bones of the foot are divided into three regions: forefoot, midfoot and rearfoot. Any of the bones of the foot can be bruised or broken (fractured) as a result of various injuries.

The forefoot consists of the toe bones (phalanges) and the five long bones (metatarsals) that attach to the toes. The midfoot consists of several strangely-shaped bones called the mid-tarsal bones, while the rearfoot consists of the heel bone (calcaneus) and ankle bone (talus).

Between each two adjacent bones is a space called a joint.

Joints are the parts of our bodies that move. This occurs because the bones are coated with a smooth material (cartilage) that allows them to glide past each other. When this cartilage wears down or is injured, a painful condition called arthritis develops. Surrounding the joints are fibrous structures called ligaments. These structures can be injured if they are overstretched (sprain) or torn (rupture).

The rearfoot bones are responsible for transmitting forces between the foot and leg. The midtarsal bones connect the forefoot to the rearfoot. Their unusual shapes and position of their joints allow transmission of forces in various directions, and over uneven terrain. The forefoot bones allow the foot to propel at the end of each step and assist with balancing while standing.

Muscles and Tendons
The muscles of the leg connect to the bones of the foot by tendons.

The tendons create movement of the foot in various directions. Those on the front of the leg (extensors) move the foot up, while those on the back of the leg (flexors) move the foot down.

The most powerful of the flexor tendons is the Achilles tendon. This tendon is frequently injured or even torn in falls and athletic activity, particularly in middle-aged men. There are other tendons on either side of the ankle that move the foot from side to side. These are called invertors and evertors.

In addition to the muscles that originate in the leg (extrinsic muscles) and attach to the foot, there are four layers of small muscles on the bottom of the foot and one layer on top. These are totally contained within the foot and are called the intrinsic muscles. These are not commonly injured.

Nerves
There are two types of nerves in the foot: motor nerves, which cause muscles to move, and sensory nerves, which provide all types of sensation.

The sensory nerves of the bottom of the foot are particularly important, because the sole of the foot is continuously in contact with the environment and help us identify when we’re standing on hot or cold or smooth or sharp surfaces.

Certain diseases such as diabetes can damage sensory nerves, resulting in a loss of protective sensation. These nerves also can be pinched due to tight or pointed shoes, a condition known as neuroma, a common cause of toe and forefoot pain.

Blood Vessels
There are two major arteries which bring blood to the foot. One is located on the top of the foot, and the other goes to the bottom of the foot. Diseases such as diabetes and atherosclerosis can damage the arteries and reduce blood flow to the foot, which can lead to loss of sensation or numbing.

Skin and Appendages
The final anatomic structure of the foot is the skin and its so-called appendages, namely, the toenails. The skin of the foot is prone to many injuries, infections and allergic reactions. The nails of the feet also can be injured or become ingrown due to shoe pressure or improper trimming, or can become infected with fungus.

Fungal infections on the feet and toenails are very common in Florida – and other warm weather climates. Typical infections include Athlete’s Foot, nail infections and ringworm of the toenails.

Fungal infections thrive in moist climates on the skin. To avoid this, be sure to thoroughly cleanse and properly dry the skin after strenuous exercise, swimming or your daily bath. Also, be sure to wear shoes and socks that allow air to circulate around the foot and toes.

Richard C. Wilson, D.P.M., is board certified by the American Board of Podiatric Surgery. He treats conditions of the foot, ankle, and leg at his two offices in Melbourne. For more information, call (321) 723-3500.