Tarsal Tunnel Syndrome

Tarsal tunnel syndrome is an mononeuropathy of the posterior tibial nerve or of one of its branches in the tarsal tunnel. It is analogous to carpal tunnel syndrome of the wrist.
== Anatomy ==
The tarsal tunnel is a bony canal found below the medial malleolus. The posterior tibialis, flexor hallucis longus, flexor digitorum, posterior tibial artery and vein, and tibial nerve all run through the tarsal tunnel. 
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== Aetiology ==
The tarsal tunnel is a tight space and so any volume-occupying lesion can lead to tarsal tunnel syndrome.
It can occur form anything that increases pressure on the tunnel such as improper foot orthoses, pressure areas in boots, and scar tissue from previous surgery. It is also seen in runner who don't have good hip stability during midstance resulting in the opposite foot hitting the tarsal tunnel as it swings forward. Excessive pronation can also lead to tension on the tibial nerve. Injuries to the posterior tibialis or flexor hallucis tendons can also lead to increased pressure in the tarsal tunnel.
The list of causes include:Radswiki, T., Baba, Y. Tarsal tunnel syndrome. Reference article, Radiopaedia.org. (accessed on 07 Mar 2022) https://doi.org/10.53347/rID-15567
* Idiopathic (40-50% cases)
* Ganglion cysts
* Bone deformity after calcaneal fractures
* Varicosities
* Tenosynovitis of the flexor tendons
* Tumours (e.g. schwannoma, lipoma)
* Accessory or hypertrophied abductor hallucis muscle
* Synovial hypertrophy
* Hindfoot valgus
* Pes planus
* Post-traumatic fibrosis
* Os trigonum
== Clinical Features ==
Patients get neuropathic pain from the tibial nerve. The pain may be aching or burning and they may complain or numbness or tingling. The pain radiates to the plantar surface of the forefoot via the medial and lateral plantar branches or the medial calcaneus via the medial calcaneal branch. In other words it can involve the sole of the foot, distal foot, toes, and sometimes the heel. It can also radiate up the medial ankle. The pain tends to be worse at night. It can also be aggravated by standing and some patients will take their shoes off when this occurs.
Look for chronic abrasions on the posterior medial ankle and oedema inferior and posterior to the medial malleolus. The triple compression test can be used to help assess for the condition. Tinel's sign may be positive over the tibial nerve posterior to the medial malleolus causing paraesthesias distally. There may be reduced sensation over the plantar surface of the foot, but this shouldn't extend onto the dorsal foot.
The most common symptoms are pain and paraesthesia in the toes, sole, or heel and the main finding at physical examination is the Tinel sign (distal paraesthesias produced by percussion over the affected portion of the nerve). Tarsal tunnel syndrome is usually unilateral.
== Differential Diagnosis ==
Occasionally compression of the tibial nerve can occur in the popliteal fossa e.g. from a Baker's cyst. Also patients may have isolated medial and lateral plantar neuropathies of the foot from trauma, fibrosis, or entrapment.
== Investigations ==
Ultrasound can visualise some of the aetiologies.
MRI can be helpful in determining various aetiologies. It can also be helpful in decision making e.g. by identifying tenosynovitis or space-occupying lesions.
Sometimes nerve conduction studies and electromyography are required.
== Treatment ==
First line treatments are NSAIDs, shoe modification, and orthotics.
Second line treatment is corticosteroid injection and this can also be helpful diagnostically.
In refractory cases surgical decompression can be offered, but surgery has a very high complication rate of 30%.Bailie DS, Kelikian AS. Tarsal tunnel syndrome: diagnosis, surgical technique, and functional outcome. Foot Ankle Int. 1998 Feb;19(2):65-72. doi: 10.1177/107110079801900203. PMID: 9498577. Surgical outcomes are more favourable with shorter durations of pain, presence of a ganglion, no history of sprains, and low work demands.Turan I, Rivero-Melián C, Guntner P, Rolf C. Tarsal tunnel syndrome. Outcome of surgery in longstanding cases. Clin Orthop Relat Res. 1997 Oct;(343):151-6. PMID: 9345220.
== References ==
Category:Foot and Ankle Conditions
Category:Mononeuropathies