What are feet? |

Structure and Functions

The anatomy of the foot is very similar to that of the hand; however, the foot is adapted to perform very different functions. The human hand has the ability to perform fine movements such as grasping and writing, while the foot is involved mainly in support and movement. Therefore, the bones and muscles of the foot tend to be heavier and function without the same dexterity as the hand.

The twenty-six bones of the foot include the tarsals, metatarsals, and phalanges. The proximal portion of the foot next to the ankle is composed of seven tarsal bones: the calcaneus, talus, navicular, cuboid, medial cuneiform, intermediate cuneiform, and lateral cuneiform. The bones are rather irregular in shape and form gliding joints; these joints allow only a limited movement when compared to other joints in the body. The calcaneus forms the large heel bone, which serves as a major attachment for the muscles that are located in the back of the lower leg. Just above the calcaneus is another large foot bone called the talus. The talus rests between the tibia and the fibula, the two lower leg bones. Interestingly, the talus is the single bone that receives the entire weight of the body when an individual is standing; it must then transmit this weight to the rest of the foot below. The cuboid and the three cuneiform
bones meet the proximal end of the long foot bones, the metatarsals.

The five separate metatarsal bones are relatively long and thin when compared to the tarsal bones. Anatomists distinguish between the five metatarsals by number. If one begins numbering from the medial (or inside) part of the foot, that metatarsal is number one and the lateral (or outside) metatarsal is number five. The distal portion of each metatarsal articulates (meets) with the toe bones, or phalanges.

Humans have toes that are very similar to their fingers. In fact, the numbers and names of the toe and finger bones, phalanges, are identical. The major differences lie in the fact that the finger phalanges are longer than the phalanges that make up toes. Hinge joints are located between each phalanx and allow for flexion and extension movements only. Human toes (or fingers) are made up of fourteen different phalanges. Each toe (or finger) has three phalanges except for the big toe (or thumb), which has only two. The toes are named in a similar way as the metatarsals; that is, the big toe is number one and the little toe is number five. The three phalanges that make up each toe (except for the big toe) are named according to location. The phalanx meeting the metatarsal is referred to as the proximal phalanx. The bone at the tip of the toe is the distal phalanx, and the one in between is the middle phalanx. Since the big toe only has two phalanges, they are called proximal and distal phalanges.

Although it seems that there is only a single arch in each foot, podiatrists and anatomists identify three arches: the medial and lateral longitudinal arches and the transverse, or metatarsal, arch. The medial longitudinal arch, as the name implies, is located on the medial surface of the foot and follows the long axis from the calcaneus to the big toe. Likewise, the lateral longitudinal arch is on the lateral surface and runs from the heel to the little toe. The transverse, or metatarsal, arch crosses the width of the foot near the proximal end of the metatarsals. The bones are only one factor that maintains arches in the feet and prevents them from flattening under the weight of the body. Ligaments (which connect bones), muscles, and tendons (which attach muscles to bones) are primarily responsible for the support of the arches. The arches function to distribute body weight between the calcaneus and the distal end of the metatarsals (the balls of the feet). They also are flexible enough to absorb some of the shock to the feet from walking, running, and jumping.

While the feet seem to be composed of only bones, tendons, and ligaments, the movements of the toes and feet require an extensive system of muscles. Most of the larger muscles that act on the foot and toes are actually located in the lower leg. Anatomists divide these muscles into separate compartments: anterior, posterior, and lateral.

The muscles of the anterior compartment move the foot upward (dorsiflex) and extend the toes. These muscles include the tibialis anterior, extensor digitorum longus, extensor hallucis longus, and peroneus tertius. The tibialis anterior is attached to the top of the first metatarsal and pulls the medial part of the foot upward and slightly lateral. All of the toes except the big toe are pulled up (extended) by the extensor digitorum longus. The extensor hallucis longus moves only the big toe upward, while the peroneus tertius is attached to the fifth metatarsal and moves the foot upward.

The muscles of the lateral compartment act to move the foot in a lateral or outward direction. The peroneus longus and peroneus brevis are attached to the first and fifth metatarsal, respectively. Using these attachments, the muscles can pull the foot laterally.

The muscles of the posterior compartment are the largest group and act to flex the foot and toes. All of these muscles share a common tendon, the calcaneus (or Achilles) tendon. As the name suggests, this large tendon attaches to the calcaneus bone. The larger, more superficial muscles include the gastrocnemius, soleus, and plantaris; these powerful muscles are commonly called the calf muscles. Also in the posterior compartment are four smaller muscles located beneath the calf muscles: the popliteus (located directly behind the knee joint), flexor hallucis longus, flexor digitorum longus, and tibialis posterior. The popliteus rotates the lower leg medially. The flexor hallucis longus flexes the big toe. The remaining toes are flexed by the flexor digitorum longus, while the tibialis posterior acts opposite the tibialis anterior to flex the foot.

Within the foot itself are some muscles known as the intrinsic foot muscles. All but one of these muscles are located on the bottom surface of the foot. This one muscle extends all of the toes except the little toe. The remaining intrinsic muscles are on the plantar (bottom) surface and serve to flex the toes.

The major vessels that provide blood to the foot include branches from the anterior tibial artery. This relatively large artery is located along the anterior surface of the lower leg and branches into the dorsalis pedis artery, which serves the ankle and upper part of the foot. Physicians often check for a pulse in this foot artery to provide information about circulation to the foot and circulation in general, as this is the point farthest from the heart. The bottom parts of the feet are supplied with blood by branches of the peroneal artery. At the ankle, this artery branches into plantar arteries, which supply the structures on the sole of the foot. The human toes receive most of their blood from branches of the plantar arteries called the digital arteries.

Disorders and Diseases

Even though the anatomy of the foot is resistant to the tremendous amount of force that the body places on it, it can be injured. Force injuries to the foot commonly result in fractures or breaks of the metatarsals and phalanges. Occasionally, the calcaneus may fracture from a fall on a hard surface. More commonly, patients complain of painful heel syndrome.

Because the shock-absorbing pads of tissue on the heel become thinner with age, repeated pressure on the heel can cause pain. Prolonged standing, walking, or running can add to the pressure, as can being overweight. One cause of pain is plantar fasciitis, an inflammation of the tough band of connective tissue on the sole. The inflammation occurs when the muscles located on the back of the lower leg that are attached to the connective tissue at the calcaneus pull under stress. This may even be associated with small fractures. X-rays may show small spurs of bone near the site of stress; however, these spurs are not believed to be the cause of pain.

Deformities of the foot at birth are fairly common and include clubfoot, flat foot, and clawfoot. The cause of these anomalies is abnormal development. The foot of the fetus normally goes through stages where it is turned outward and inward but gradually assumes a normal position by about the seventh month of gestation. In the case of clubfoot, arrested development in the stage when the foot is turned inward causes the muscles, bones, and joints to develop in this abnormal anatomical position. At the time of birth, the deformity is readily observable and the foot immobile. Treatment includes splints, casting, and surgery. If treatment is begun at birth, the foot may look relatively normal after approximately one year.

Almost everyone is born with feet that are flat because the arches do not begin to develop until the ligaments and muscles function normally. In most people, the arches are fully formed by the age of six. In some individuals, however, the ligaments and muscles remain weak and the feet do not develop a normal arch. Flat feet can also develop in adult life, at which time they are called “fallen arches.” Body weight moves along a precise path during walking or running, beginning with the heel touching the ground. Then, as the foot steps, the arch receives the forces pushing down on the foot. Because the bones, muscles, and ligaments form an arch in the foot, the arch can deform slightly and absorb some of the downward force. With further movement, the weight passes to the ball of the foot (the distal metatarsals). A fallen arch has lost this flexibility and shock-absorbing capability. The arch “falls” because of improper weight distribution along the foot, causing the arch to stretch excessively and to weaken with time. Without proper arch support, the foot begins to twist inward, or medially, causing the body weight to be transmitted to the inside of the foot rather than in a
straight line toward the toes. This problem often occurs in runners who have improperly fitted shoes or a poor running style (although anyone can suffer from fallen longitudinal arches, regardless of the individual’s level of physical activity). As a runner increases distance and speed without correcting his or her shoes or running form, the force applied to the feet increases. Fallen arches appear to occur particularly in runners or joggers who exercise on hard surfaces without proper technique or arch support.

A number of disorders can affect the skin of the foot. Corns are small areas of thickened skin on a toe that are usually caused by tight-fitting shoes. People with high arches are affected most because the arch increases the pressure applied to the toes during walking. If the corn becomes painful, the easiest treatment is for the person to wear better-fitting shoes. If the pain persists, a clinician can pare down the growth with a scalpel.

Plantar warts appear on the skin of the sole and are caused by a papillomavirus. Because of pressure from the weight of the body, the plantar
wart is often flattened and forced into the skin of the sole. The wart may disappear without treatment. If it persists, surgery or chemical therapy can be used to relieve the discomfort.

Athlete’s foot is a common fungal infection that causes the foot to become itchy, sore, and cracked. It is usually treated with antifungal agents such as miconazole. Preventive measures include keeping the feet dry and disinfecting areas where the fungus may live, such as shower stalls.

Another common deformity is a bunion, which is a bursa (fluid-filled pad) overlying the joint at the base of the big toe. Normal structure of the first metatarsal, first phalange, and their joint is necessary to withstand the force applied to them in everyday activities. A
bunion is caused by an abnormal outward projection of the joint and an inward projection of the big toe. Treatment involves correcting the position of the big toe and keeping it in a normal position. Sometimes surgery is necessary if the tissues become too swollen. In fact, some severe cases of bunions have required complete reconstruction of the toe. Unless treated, a bunion will get progressively worse.

Gout is a metabolic disorder, mainly found in men, which causes uric acid crystals to form in joints. Even though any joint can be affected, the big toe joint is likely the major site for gout because it is under chronic stress from walking. The joint is usually red, swollen, and very tender and painful. The first attack usually involves only one joint and lasts a few days. Some patients never experience another attack, but most have a second episode between six months and two years after the first. After the second attack, more joints may become involved. Treatment includes anti-inflammatory drugs and colchicine. These drugs help reduce the pain by decreasing the amount of inflammation around the joint. Physicians may also prescribe allopurinol to reduce the amount of uric acid that the body produces. Drugs are also available that increase the kidneys’ ability to excrete uric acid; examples of these agents are probenecid and sulfinpyrazone.

Perspective and Prospects

Even though the feet constitute a relatively small area of the body, ailments of the feet afflict more than half the world’s population. For a long time, disorders of the foot were not taken as seriously as those found in other parts of the body. It is now known, however, that poor foot health can have serious effects. For example, in children a painful foot condition not properly diagnosed and treated can result in lost school days and decreased participation in other activities. More important, an uncorrected congenital abnormality, if neglected, could have irreversible consequences. For the elderly, foot problems hinder or prevent normal activities such as taking care of personal needs, exercising, and socializing. Anything that affects the feet affects that individual’s overall health and well-being.

Because of the potentially devastating problems of improper foot care, a branch of medicine developed that specifically addresses problems of the feet. Physicians known as podiatrists practice a specialized branch of medicine called podiatry. It is the job of the podiatrist to assess the cause of the foot problem and the patient’s general medical condition in determining the need for and the course of treatment. This assessment often calls for contact with the patient’s primary care
physician for access to the patient’s medical records, as many diseases affect the whole body but present signs and symptoms in the feet. The podiatrist or other physician, such as an orthopedist, will evaluate a disorder through physical exams, laboratory tests, and anatomical tests to examine the internal structures; the latter may include X-rays, computed tomography (CT) scans, or magnetic resonance imaging (MRI). The physician will then diagnose and begin treating the disorder using surgery, medical therapy, or physical therapy.

As more individuals become physically active throughout their lives, clinicians who practice
sports medicine are paying closer attention to problems of the foot. Many people seek to improve their health by walking, jogging, and bicycling. All these activities have proven to be excellent for maintaining cardiovascular health, but all place additional stress on the foot. Physicians who counsel patients on physical fitness programs attempt to identify individuals who may be injury-prone. Failure to recognize an anatomical anomaly of the feet could lead to an injury or series of injuries that restrict certain activities or even cause permanent damage. Occasionally, individuals are too enthusiastic about their exercise program and experience overuse injuries involving the feet. Such injuries may cause a sudden cessation of the physical activity and may have a significant demoralizing effect on individuals who finally decide to take steps to improve
their health and well-being.

People commonly neglect their feet and underemphasize the importance of the normal functional anatomy of the foot. Individuals who experience a foot injury, however, begin to appreciate the absolute importance of this rather complex but often overlooked structure.

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