Tarsal Tunnel Syndrome

Tarsal tunnel syndrome sometimes referred to as tibial nerve dysfunction or posterior tibial nerve neuralgia, is an entrapment neuropathy that is associated with the compression of the structures within the tarsal tunnel. It is similar to carpal tunnel syndrome of the wrist although much less common.The tarsal tunnel is a narrow fibro-osseous space that runs behind and inferior to the medial malleolus. It is bounded by the medial malleolus anterosuperiorly, by the posterior talus and calcaneus laterally, and is held against the bone by the flexor retinaculum which extends from the medial malleolus to the medial calcaneus and prevents medial displacement of its contents. The tarsal tunnel includes multiple important structures. It contains the tendons of the posterior tibialis, flexor digitorum longus (FDL), and flexor hallucis longus (FHL) muscles. The posterior tibial artery and vein, as well as posterior tibial nerve (L4-S3), also pass through it. The orientation of these structures within the tarsal tunnel is noteworthy. From medial to lateral, they are the tibialis posterior tendon, FDL tendon, posterior tibial artery and vein, posterior tibial nerve, and FHL tendon.The posterior tibial nerve passes between the FDL and FHL muscles before it bifurcates in the tarsal tunnel, forming the medial and lateral plantar nerves. In 5% of people, the bifurcation occurs before the tarsal tunnel. The medial plantar nerve passes deep to the abductor hallucis and FHL muscles and provides sensation to the medial half of the foot and first 3.5 digits and motor function to the lumbricals, abductor hallucis, flexor digitorum brevis, and flexor hallucis brevis. The lateral plantar nerve passes directly through the abductor hallucis muscle belly and provides sensory innervation of the medial calcaneus and lateral heel and motor function to the flexor digitorum brevis, quadratus plantae, and abductor digiti minimi. The medial calcaneal nerve typically branches off of the posterior tibial nerve proximal to the tarsal tunnel and provides sensory innervation to the posteromedial heel. In 25% of patients, it branches off of the lateral plantar nerve or runs superficial to the flexor retinaculum.