The term tarsal tunnel syndrome was described by Keck in 1962. It is characterised by burning pain in medial aspect of ankle and foot and paraesthesia along the distribution of medial and lateral plantar nerves, which is aggravated by standing. Pain may radiate into the leg. Sensory deficit may be seen in long standing cases, but motor deficits are rare. Seen more frequently in those who stand for prolonged period and in those with extremely pronated feet.
Tarsal tunnel is located in the medial aspect of ankle and foot. Roof is formed by the flexor reticulum and the floor is formed by the medial surface of talus, sustentaculum tali and medial surface of calcaneum. Flexor retinaculum is triangular in shape with its apex attached anteriorly to the medial malleolus and the base attached posteriorly to the medial tuberosity of calcaneum. It is thickest at the inferior margin where it splits to envelop the abductor hallucis. Distally it reunites and merges with the plantar fascia. Fibrous septae that pass from the undersurface of flexor retinaculum to periosteum of calcaneum, divide the tunnel into 4 compartments. These compartments enclose the tibialis posterior, flexor digitorum longus, tibial neurovascular bundle and flexor hallucis longus respectively from anterior to posterior.
The tibial nerve divides into medial and lateral plantar nerves and medial calcaneal nerve at the ankle. This division occurs beneath the retinaculum in 93% and proximal to the retinaculum in 7%. Medial calcaneal nerve passes posteriorly piercing the retinaculum to supply the skin over the medial aspect of heel, it may arise as a branch of tibial nerve or lateral plantar nerve. Distal to the retinaculum, the medial and lateral plantar nerves are separated by the transverse interfascicular fascia. Medial plantar nerve supplies most of the sensory supply to the sole, it supplies the abductor hallucis, flexor hallucis brevis, flexor digitorum brevis and first lumbrical muscles. The lateral plantar nerve supplies the rest of muscles.
Tarsal tunnel syndrome may be caused by extrinsic or intrinsic pressure on the tibial nerve or its terminal branches underneath the flexor retinaculum. Cause of pressure on nerve may be hindfoot deformities like varus or valgus, bony spikes due to fractures, anomalous muscles, mass lesions such as ganglions or schannoma. In 50% the cause of compression is mechanical due to some identifiable cause but no cause can be found in the other 50%.
The resultant symptoms depend on the extent of nerve involvement, and the site of compression, which may result in variants of the syndrome. The patients usually presents with pain and paraesthesia over the sole and medial aspect of ankle. Pain may radiate proximally and distally. Tinel sign may be elicited over the tarsal tunnel region and it is the most sensitive sign. Several special tests are described for the diagnosis of tarsal tunnel syndrome. Kinoshita test(dorsiflexion-inversion test) is dorsiflexion and eversion of ankle and dorsiflexion of foot for 10 seconds. If it produces paraesthesia then the test is positive for tarsal tunnel syndrome. Linscheid test is application of digital pressure below and behind the medial malleolus for one minute. Lam test is forced inversion and medial rotation of foot for 30 seconds. Tourniquet test is inflation of a tourniquet over the leg to produce venous stasis for one minute. Percussion over the nerve at the ankle may produce pain extending proximally in the course of tibial nerve and this is called Valleix phenomenon.
A clinical triad named HPT(Heel pain triad) Syndrome has been described by Labib, which includes plantar fasciitis, posterior tibial tendinitis and tarsal tunnel syndrome.
Electro diagnosis is difficult as the tibial nerve becomes deep immediately proximal to the tarsal tunnel. Both sensory and motor conduction studies should be done. Sensory and motor latencies may be prolonged and nerve conduction velocity may be decreased. Ultrasound, CT and MRI may help in the identification of bony or soft tissue lesions.
Differential diagnosis include tendinitis (tibialis posterior, FDL or FHL), plantar fasciitis, subtalar or ankle arthritis, hindfoot deformity, stress fracture, peripheral vascular disease, peripheral neuropathy, lumbar disc prolapse and varicose veins.
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Keck C: The tarsal tunnel syndrome. J Bone Joint Surg Am 1962:44:180.
Labib SA, Gould JS: Heel pain triad (HPT) the combination of plantar fasciitis, posterior tibial tendon dysfunction and tarsal tunnel syndrome: Foot Ankle Int 2002:Mar 23(3):212.
Kinoshita M, Okuda R, Monkawa J: A new test for TTS. J Bone Joint Surg Am 2002:Sept;04A(9):1714-5.
Lam SJ. Tarsal tunnel syndrome. J Bone Joint Surg Br. 1967;49:87-92.
Linscheid RL, Burton RC, Fredericks EJ. Tarsal-tunnel syndrome. South MedJ. 1970;63:1313-23
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