Tarsal tunnel syndrome is caused by the entrapment of the tibial nerve.

The tibial nerve follows a curving route down the back of the leg to the ankle, where it turns 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 vein and artery are surrounded by muscles.

Along the top of these structures lies the laciniate ligament, which forms the roof of the four compartments. There is little room for expansion if any of these structures becomes enlarged or if a foreign object intrudes into the area. If anything impinges on the space occupied by the tibial nerve (i.e., the tarsal tunnel), entrapment occurs.