What is the Tarsal Tunnel?
The tarsal tunnel is a narrow space that lies on the inside of the ankle, next to the ankle bones. It is covered with a thick ligament (the flexor retinaculum) that protects and maintains the structures located within the tunnel (arteries, veins, tendons, and nerves). One of these structures is the posterior tibial nerve, which is where tarsal tunnel syndrome is located.

What is Tarsal Tunnel Syndrome?
Tarsal tunnel syndrome is a squeezing of the posterior tibial nerve. This nerve runs along the inside of the ankle into the foot, and symptoms can occur anywhere along it's length. It is very similar to carpal tunnel syndrome in the wrist. 

Symptoms

• Tingling, burning, or an electrical shock sensation
• Numbness
• Pain, including shooting pain

These are all typically felt on the inside of the ankle and/or on the bottom of the foot. It can occur in just one spot, or extend all the way from the calves to the toes. 

Causes

• Flat feet or fallen arches
• Varicose veins, ganglion cyst, swollen tendons, arthritic bone spurs
• Injuries, such as ankle sprains
• Obesity
• Diabetes or arthritis

All of the above causes cause compression of the posterior tibial nerve.

Diagnosis
Your podiatrist will examine your foot thoroughly to determine if there is any loss of feeling, as well as feeling for any masses that may be causing compression. If a mass is suspected, the doctor will most likely order an MRI. Other special studies may also be ordered if the condition shows no improvement with non-surgical treatment.