Tarsal tunnel syndrome is the foot equivalent to carpal tunnel syndrome in the wrist. Both are conditions that involve pressure or strain on a nerve, the result being numbness, burning, and/or tingling. Unlike carpal tunnel syndrome, which is often caused due to one's occupation ( such as with heavy keyboard use), tarsal tunnel syndrome is often due to one's foot structure and is not necessarily restricted to those who are overly active on their feet.
The tarsal tunnel is a region just under the ankle on the medial side of the foot, or the side where the big toe sits. It is surrounded by various ligaments, muscles, and connective tissue. Within this 'tunnel' of tissue lies several structures, including an artery, a vein, and the trunk and branches of the posterior tibial nerve. This nerve gives sensation and fine muscle control to the bottom of the foot and heel. The nerve is dependent on a loose and obstruction-free passage through the tarsal tunnel to function properly. There are many situations in which this is not the case, and nerve irritation and damage can be the result. The most common scenario seen is in individuals with flat feet, where the foot naturally rolls outward. This causes a small amount of strain to the tissues on the side of the foot and ankle that cover the top of the tarsal tunnel. As they become chronically strained over many years of walking with flat feet, these tissues may become scarred, and less flexible. This will eventually put pressure on the nerve below, and begin a process of nerve damage due to constant pressure. Fractures and severe sprains of the inside of the ankle can also cause scar tissue to form, which will place pressure on the nerve. Other sources of pressure can include varicose vein development in the vein that runs with the nerve through the tarsal tunnel, or some other type of mass. Imagine holding down on one's own 'funny bone' (which is in actuality a nerve) until the arm becomes numb and tingling, and then never releasing the pressure. This is somewhat similar to the process that is occurring at the tarsal tunnel. The result will be a subtle numb sensation in the heel or sole, followed by burning or tingling pain in later stages. Sharp, stabbing pain that may shoot down the foot or up the inside of the leg is also commonly seen. Walking becomes very painful, and at times the pain can even extend into periods of rest.
Diagnosing this condition is fairly easy, as examination of the region around the nerve usually provides enough information. Additional tests may be needed in cases that may be due to nerve entrapment further up the body (such as in the back). A nerve conduction velocity test (NCV) will determine where nerve signals slow down in the leg. If the area of slowdown is strictly in the tarsal tunnel, spinal problems can probably be ruled out. Unfortunately, this test is not completely accurate and at times may show there is no nerve signal slowdown even though it is very clear that tarsal tunnel syndrome is present. If a mass or varicose vein is suspected as the culprit of the nerve irritation, a MRI scan can be obtained to help the doctor visualize the soft tissue around the tunnel, something an x-ray cannot do.
Treatment involves getting rid of both the active inflammation and the underlying cause of the nerve irritation. Anti-inflammatory treatment includes oral medication, as well as steroid medication carefully injected around the tarsal tunnel. Icing is used, as well as physical therapy in some cases. One's walking, standing, and athletic activity must be reduced. The side of the ankle can be braced with an ankle brace, and severe cases may need a walking boot to take away more pressure. For those with flat feet as the underlying cause, the use of long term prescription orthotic shoe inserts can help keep the condition stable and prevent reoccurrence once the inflammation is resolved. There are many instances, however, that the above treatment does not provide sufficient relief. This is especially true if there is a lot of scar tissue, or if a mass or varicose veins are present. In these cases, surgery is needed to release the pressure off of the nerve, either by freeing up tight scar tissue or removing any mass or vein branch pushing on the nerve. This procedure is usually quite successful, although excessive post-surgical scar tissue can occasionally develop, starting the process over again.