The tarsal tunnel is a narrow space on the inside aspect of the ankle joint formed by the ankle bones and the flexor retinaculum. Tarsal tunnel syndrome is a compression neuropathy that occurs as a result of the posterior tibial nerve being compressed inside the tarsal tunnel. The resultant pain can be felt anywhere in the ankle and foot, and may be severe. There are a number of causes of tarsal tunnel syndrome, although in some patients the exact cause cannot be determined.
Flat Feet
When a person has flat feet, the arch of the foot collapses. This forces the heel to tilt outward, putting strain on structures inside and around the ankle joint. The strain is particularly transmitted to the area of the tarsal tunnel, where nerves and tendons pass through. To accommodate the strain, nerves, tendons and blood vessels may realign their positions relative to one another. However, often such positional realignment is not enough to avert tibial nerve compression inside the tarsal tunnel. The result is that the compressed tibial nerve produces symptoms of pain anywhere along its path in the ankle and foot.
Systemic Disease
The tibial nerve may react to conditions that are not directly mechanical in nature. Rheumatoid arthritis and diabetes are known to cause tarsal tunnel syndrome due to their effect on adjacent tissues. Arthritis produces inflammation and swelling in or near the tarsal tunnel. The swelling subsequently results in compression of the tibial nerve resulting in pain. Diabetes produces enlargement of blood vessels in the area due to increased glucose content. Since blood vessels and nerves often are found together, this can exert pressure on the tibial nerve. Obese patients often are more prone to tarsal tunnel syndrome as a result of the additional vertical pressure placed on the ankle.
Ankle Injury
Tarsal tunnel syndrome can result from an ankle injury as would occur with an ankle sprain, dislocation or fracture. This happens because injury frequently produces inflammation and swelling. If the swelling is close to the tarsal tunnel and the tibial nerve, then the swelling can impinge on the nerve causing compression along with the attendant pain. In addition, sometimes dislodged bone chips near the tarsal tunnel can migrate toward the tibial nerve and lodge upon it resulting in nerve compression and pain.
Other
Cysts or tumors in and near the tarsal tunnel can be of such volume as to compress the tibial nerve resulting in pain. Additionally, inflammation of a tendon as occurs with excessive straining, can result in tendonitis in the ankle. If the tendonitis produces swelling near the tibial nerve then the result can be nerve compression which results in pain. Other factors that can cause tarsal tunnel syndrome include varicose veins in the region or bone spurs around the tibial nerve. Both of these may cause tibial nerve compression with the resultant symptoms of tarsal tunnel syndrome.
