Tarsal Tunnel Syndrome

Definition

Similar to the more familiar carpal tunnel syndrome, a condition that affects the wrist, tarsal tunnel syndrome is caused by entrapment of a nerve - in this case the tibial nerve.
The tibial nerve follows a long, curving route down the back of the leg to the ankle, where it turns medially and curls below the inside of the ankle. There are four compartments in this region. In three of them, muscles are routed from the leg to the foot. In the fourth, the tibial nerve and the posterior tibial artery are surrounded by muscles. Along the top of these structures lies the laciniate ligament, which forms the roof of the four compartments. Therefore, there is virtually no room for expansion if any of these structures becomes enlarged or if a foreign object intrudes into the area.

Symptoms

If anything impinges on the space occupied by the tibial nerve - the tarsal tunnel - entrapment is said to occur. Entrapment compresses the nerve, causing pain, burning and tingling on the sole of the foot. Normally, this pain is relieved by rest and elevation or massage. Unlike the heel pain caused by plantar fascitis (see special section on Heel Pain), which is worst in the morning, the pain caused by tarsal tunnel syndrome usually worsens as the day progresses.

Causes

Tarsal tunnel syndrome most commonly occurs in active adults, but also can occur in children. The burning or tingling sensation it causes is a function of the compressed tibial nerve trying to send signals between the foot and brain. An analogy can be made between the nerve and a garden hose. If a hose is drawn around a sharp corner, tension will be created at the point of the bend. If the hose were to be pulled even tighter, it would kink, and the flow of water through it would be restricted. If someone stepped on the hose, the flow would be reduced even further.

In tarsal tunnel syndrome, the same types of forces are applied to the tibial nerve. When it is compressed by another structure, the neurological impulses through the nerve are restricted. This causes sensations such as pain, burning and tingling. In many cases, this compression is caused by an adjacent muscle, which grows too large for the area. People with exceptionally flat feet also can develop tarsal tunnel syndrome because the flattened arch causes the muscles and nerves running around the ankle to change their route slightly, compressing the tibial nerve. In other cases, compression results from a cyst that forms in this area. Systemic diseases like rheumatoid arthritis and diabetes also can cause the syndrome.

Another common cause is trauma to the ankle, such as a fracture. When the injury heals, fibrous tissue develops in the area, similar to an internal scar. If too much scar tissue forms, it can restrict movement in the tarsal tunnel and cause entrapment of the nerve.

Treatment

Conservative treatment, such as wearing arch supports and wider shoes, sometimes produces limited success in relieving the discomfort of tarsal tunnel syndrome. If inflammation of the nerve is causing the compression, nonsteroidal anti-inflammatory drugs (NSAIDs) may be prescribed. Steroid injections also may prove effective. If the problem is caused by flat feet, custom orthotics can help restore the foot's natural arch.

If these attempts fail, more aggressive surgical treatments often succeed. An incision can be made behind and below the inside of the ankle, through which the surgeon can cut the laciniate ligament. This will provide room for expansion of the nerve. If a cyst is impinging on the nerve, it can be removed as well. This procedure should provide enough space to prevent the nerve from being compressed in the future.