Background and indications: Tarsal tunnel syndrome is an entrapment neuropathy that involves compression of the posterior tibial nerve or its branches within the fibro-osseous tunnel that lies beneath the flexor retinaculum. Symptoms may involve pain at the medial aspect of the ankle extending into the medial aspect of the foot, the plantar aspect of the foot, and the toes. Patients may experience paresthesias as well as burning pain. Periodically, the patient’s pain can even radiate proximally along the medial calf. Depending on the compression site and the specific nerve branch involved, clinical symptoms may be more localized to the medial plantar aspect of the heel. The cause is often biomechanical faults and intrinsic foot structure that leads to overpronation and increased tension on the posterior tibial nerve within the tarsal tunnel. Branches of the posterior tibial nerve (medial and lateral plantar nerves) can be entrapped by synovial cysts, bone and other joint abnormalities, tumors, tenosynovitis, or vascular anomalies. Ultrasound provides an excellent image guidance technique to place local anesthetic within the tarsal tunnel and around the posterior tibial nerve or its branches. On physical examination, a positive Tinel sign can often be elicited over the posterior tibial nerve under the flexor retinaculum. A triple compression stress test (TCST) is a physical examination test that has been described where the ankle is placed in full plantar flexion and the foot inverted and consTant digital pressure applied over the posterior tibial nerve. This will replicate paresthesias and pain and has been shown to have a sensitivity of 85.9% and a specificity of 100% for tarsal tunnel syndrome diagnosis.

Anatomy: The tarsal tunnel is a fibro-osseous tunnel that extends from the posterior medial aspect of the ankle to the medial aspect of the plantar region of the foot. It is divided into an upper (tibiotalar) compartment and a lower (talocalcaneal) compartment. The lower tarsal tunnel (Fig. 71.1) is covered by the flexor retinaculum (created by the fusion of the superficial and deep aponeuroses of the leg) and the abductor hallucis muscle with its fascia. Its osseous floor is formed by the posteromedial aspect of the talus, the inferomedial aspect of the navicular bone, and the medial aspects of the sustentaculum tali and calcaneus. Typically, the posterior tibial nerve is found within the upper tarsal tunnel, which trifurcates into its terminal branches just above the medial malleolus. These branches are the medial and lateral plantar nerves and the medial calcaneal nerve, (Fig. 71.2). The medial calcaneal nerve can also branch from the lateral plantar nerve, and there are many other anatomical variations.

The medial and lateral plantar neurovascular bundles are separated by the interfascicular septum. Within the tarsal tunnel lie three imporTant tendons. Starting from the anterior position just behind the medial malleolus lies the tibialis posterior tendon, next is the flexor digitorum longus, and, finally, the flexor hallucis longus in the most posterior position. These muscles can be remembered by the simple mnemonic Tom (Tibialis posterior), Dick (flexor Digitorum longus) and Harry (flexor Hallucis longus) listed from anterior to posterior. Typically, one artery (the posterior tibial artery) and two veins on either side of the artery can

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