Plantar fasciitis is the most common cause of heel pain. This condition is simply inflammation of the plantar fascia, a strong strap-like tissue divided into three bands found on the bottom of the foot. This tissue begins attached to the heel bone, and runs the length of the foot to the bottom of the toe bases. The plantar fascia can become injured due to a variety of reasons. The majority of the time, the fascia becomes injured simply as a result of walking or being active while having a certain foot structure. People with flat feet commonly get this condition because the foot becomes strained with every step when flat. The resulting strain over many years results in eventual microscopic damage and inflammation to the plantar fascia, which stretches as the foot flattens. This is accelerated when some minimal injury occurs, like stepping off a curb or onto a ladder awkwardly. After awhile, the inflammation can become significant enough that pain is actually felt. People with high arches can develop plantar fasciitis, but for a different reason. High arches do not flatten much with walking and standing. Unfortunately, some level of flattening is needed to effectively absorb shock when walking. Since high arched feet do not absorb shock well, the tissues on the bottom of the foot and heel take the brunt of the pressure of the foot pressing actively on the ground with the weight of the body behind it. This shock eventually irritates the plantar fascia, either at the point it begins from the heel bone, or somewhere in the middle of the arch.
Plantar fasciitis can also develop when one damages it directly in an injury. One can injure their plantar fascia by either stepping on a protruding object that bruises the heel or arch (like a root, stone, high door threshold, toy, or other hard object), or by directly straining the tissue after excessive use of a ladder or shallow stairs. Injuries that force the foot upward suddenly can strain the fascia, and can even cause the fascia to rupture or tear across its width.
Plantar fasciitis can have several different symptoms depending on the individual, but most commonly is felt as heel or arch pain that begins as soon as one arises from bed or from a seated position. After a few steps or a few minutes, the pain begins to decrease but eventually returns as activity increases. It rarely ever hurts when one is at rest for awhile, and does not wake people up with pain in the middle of the night. The pain can feel sharp, stabbing, throbbing, or simply aching. Burning or tingling pain usually indicates involvement of nerves that are positioned near the fascia, or an entirely different condition (such as tarsal tunnel syndrome or lower back nerve problems). Plantar fasciitis pain is usually worse when one is barefoot or in a less supportive shoe. It is rare for one to be able to see actual swelling or bruising at the heel or arch, and when these are present this usually indicates a fascia rupture or tear.
Bursitis and Heel Bruises
Direct injuries to the bottom of the heel can produce pain that is independent of the fascia. The bottom of the heel contains a small network of nerves, as well as fat padding. A small pillow of tissue can also be found in this area, and is known as the subcalcaneal bursa. This pad of tissue, or bursal sac, is part of a system of little shock absorbers that protect prominent bone tissue throughout the body. People have bursal sacs throughout the body, but under the heel one is not born with it. They develop over time after the bottom of the heel receives chronic stress and pressure. I tend to see these form and become inflamed more readily in people that have a heel bone with more of a pointed shape to the bottom of the heel. Gradual pressures causes inflammation to form in these bursal sacs, and direct injury to the heel tissue, such as when one steps on a rock or other hard object, can also result in inflammation to the bursa (bursitis), or simply may cause a bruise to form. The plantar fascia can become injured with this tissue, or the bursitis and bruise can form independently.
The result is the sensation of sharp pain or strong aching when direct pressure is applied to the heel, particularly when it strikes the ground during walking. Pain is rarely present when one is at rest, and generally the pain stays in the direct undersurface of the heel without extending to the arch or ankle.
Tarsal Tunnel Syndrome
The tarsal tunnel is a passageway on the inner side of the ankle (the side of the big toe) where a big bundle of blood vessels and a large nerve passes through. It is surrounded by firm fibrous tissue that can pinch, or create abnormal pressure, on the tissue within it. In particular, the nerve that runs within it, called the posterior tibial nerve, can become irritated. A similar nerve irritation occurs in the wrist in the more commonly known carpal tunnel syndrome. The posterior tibial nerve allows for sensation to the entire bottom of the foot, as well as the inner side of the foot and heel. It can be sensitive to irritation from either a narrowing of the tarsal tunnel through injury or chronic stress (such as seen in people with flat feet), or by cysts, varicose vein branches, or other small masses that physically push on the nerve.
When this nerve is irritated by tissue impinging on it in the tarsal tunnel, the result can be abnormal nerve function. In particular, the bottom of the foot and the heel can feel numb, or there can be a sharp, burning, or tingling pain present. Much of the pain is felt directly on the inner side of the heel. However, early tarsal tunnel syndrome can feel strictly as if the pain is in the bottom of the heel. This is due to referred pain, or pain that is sensed at the end of the nerve but is generated or referred from the point where the nerve is actually irritated, which is closer to the ankle. The pain is felt more with activity, like in plantar fasciitis. However, unlike fasciitis, the problem is not limited to the arch, and the pain can remain in the foot even during rest if the tarsal tunnel is irritated enough. In addition to the nerve in the tarsal tunnel itself, there are several branches of this nerve that come off of it before and after the tarsal tunnel that can cause similar symptoms if they are inflamed by injury or foot strain from abnormal foot structure.
Other Causes of Pain on the Bottom of the Heel
There are numerous other causes for pain on the bottom of the heel besides plantar fasciitis, tarsal tunnel syndrome, and bursitis. These causes are far less common than the others combined, but do develop from time to time.
Lower back spinal disease:
The lower back is home to the end of the spine, and subsequently nerves that supply the legs with sensation and muscle control. In a process similar to the above tarsal tunnel syndrome, spinal nerve root branch damage through arthritis or a slipped disk can create pain that is felt further down in the leg. Back pain usually accompanies this, but not always. The typical symptoms including an electrical shooting, tingling, or burning down the leg, but the symptoms can also be much more limited in some cases. If specific parts of the nerve root branch are affected, the heel or arch may be the only part of the foot that feels painful. The heel itself may be painful to the touch, but in this case it is most often due to oversensitization of the pressure receptors in the foot as a result of the lower back nerve damage. Heel pain in this situation does not respond well to treatment of the foot itself, and the lower back must be addressed. Unfortunately, this connection is difficult for people with no medical training to accept, as it is hard to conceptualize that the lower back can cause foot pain, and treatment recommendations are often dismissed or ignored.
Stress fracture of the heel bone (calcaneus):
Stress fractures of the stout heel bone are uncommon, but can develop and are misinterpreted as plantar fasciitis. Stress fractures can take several months to appear on x-rays, and when they do appear in the heel bone they can be difficult to see. For this reason stress fractures are often missed initially. Imaging studies like MRI or a bone scan can demonstrate stress fractures early on, but unless one is suspected these expensive tests are rarely performed in the initial stages of heel pain treatment. The foot needs to be immobilized for treatment and heel pain relief, and many traditional aspects of plantar fascia treatment, like anti-inflammatory medications, will actually stress fracture healing.
Inflammation from rheumatoid arthritis and other inflammatory diseases:
There are a whole group of conditions that cause inflammation throughout the body to bone and joint tissue. These conditions are called systemic arthropathies, and there are numerous diseases in this category. Fibromyalgia is also part of this group. Some inflammatory bowel diseases can also cause bone and joint pain, especially in the heels. The tissue covering the bottom of the heel bone will become inflamed and painful, and fluffy bone spurring can occur. Differentiating these conditions from plantar fasciitis can be difficult, as the heel is painful in a similar location in each condition. The contribution of these conditions should be considered when heel pain is not responding to traditional treatment.
Bone tumors do develop in the foot, both benign and malignant, and some cancers elsewhere in the body can metastasize to the foot. Malignant bone cancer in the foot is RARE, but it can happen and in its early states can cause heel pain if the heel bone is involved. More commonly, but still rare overall, benign bone tumors can develop that cause similar heel pain. Most of the time these lesions are seen on regular x-ray, but in their earliest stages no bone changes are immediately visible. Despite their rarity, if heel pain does not respond at all to treatment, repeat x-rays are a good idea to rule out these rare tumors, and any suspicious findings should be followed up with a CT or an MRI. Benign bone tumors are usually easily addressed by simple removal and bone packing to fill the resulting gap, but malignant life-threatening tumors may need more aggressive care, including leg amputation to save one’s life.
A simple cause of heel pain on the bottom of the heel can include issues found directly on the skin, such as calluses and warts. Callus do form on the heel skin as they do elsewhere, and often when on the bottom of the heel can have a hard central core that can be painful to walk on. Additionally, viral infections can cause hard lesions to form on the heel (as well as elsewhere on the bottom of the foot). Known as warts, these sometimes painful skin lesions may last for many years if untreated, and can make bearing weight painful.
A final common cause of heel pain that does not involve the plantar fascia can be the retention of a foreign body in the skin or deep heel tissue from a previous puncture wound. Puncture wounds of small sharp objects can sometimes be missed or dismissed as a more minor injury. The material that is left behind in the skin will cause an inflammatory reaction, and even be walled off by the body inside a capsule of sorts. The resulting inflammation and/or mass in the heel will cause heel pain, and can be mistaken for plantar fasciitis if it is in a specific location.
A Word About Spurs on the Bottom of the Heel
Heel spurs are often blamed by the general public for most heel pain. In actuality, spurs rarely ever cause pain in the bottom of the heel. The reason for this is related to the shape and orientation of the spur on the bottom of the foot, as opposed to spurs on the back of the heel (which can cause pain). A spur on the bottom of the heel usually develops as a response to traction, or pulling, on the heel bone by arch tissue attached to the front part of the bottom of the heel bone. This tissue is usually always the plantar fascia, which stretches away from the heel bone as the foot flattens. When the flattening is excessive, the tugging of the fascia stimulates the outer layer of the bone to create more bone. Over time, this bone formation results in a long extension away from the bottom of the heel bone, but parallel to the ground. The shock generated in high arched feet can also generate this reaction, but this is far less common. The reason these spurs do not result in actual pain is that they a re positioned parallel to the ground, so one is walking WITH the spur, and NOT on TOP of it. Since the spur is not digging into the heel pad tissue, it essentially becomes an extension in the length of the bottom of the heel bone. The pain therefore comes from the inflammation in the tissue that stimulated the bone growth, namely the plantar fascia. It is also not uncommon for someone to have a heel spur incidentally noted on an x-ray for some other condition, and never have ever experienced heel pain. This is because the traction that produced the spur, namely the strain of the plantar fascia, does not always result in inflammation that turns into plantar fasciitis. Some people can go their entire lives with heel spurs and not have a day of heel pain. There is an exception to the above explanation. Some conditions that affect joints, namely the autoimmune arthritic diseases (like rheumatoid arthritis), can produce small fluffy spurs that face towards the bottom of the heel bone tissue into the soft tissue on the bottom of the heel. By nature, these fluffy spur reactions are already inflamed, and their presence into the bottom of the heel causes inflammation of the tissue under the heel bone. These spurs are independent of the fascia, and are painful in and of themselves.