Tarsal Tunnel Syndrome refers to the entrapment of the posterior tibial nerve, which passes under the flexor retinaculum of the osteofibrous tarsal tunnel, behind the medial malleolus of the distal tibia.
The tibial nerve is a medial branch of the sciatic nerve that crosses the popliteal fossa and passes under the tendinous arch of the soleus muscle to supply the tibialis posterior, the flexor digitorum longus and the flexor hallucis longus.
The posterior tibial artery, nerve and vein are also found in the tarsal tunnel.
Within the tarsal canal, the posterior tibial nerve bifurcates into the medial and lateral plantar nerves which innervate the plantar surface of the medial three and a half digits and the lateral one and a half digits in addition to the sole area.
The posterior tibial nerve could be compressed at multiple sites – in the proximal tarsal tunnel under the flexor retinaculum or in the distal portion of the tunnel at the level of the abductor hallucis muscle (where the plantar nerves are located).
Other potential nerve entrapment sites include the deep fascia of abductor hallucis, the dorsal extension of lateral border of plantar aponeurosis and the dorsal extension of lateral border of the lateral band of plantar aponeurosis.
The most common aetiologies of tarsal tunnel syndrome relate to repetitive trauma such as calcaneus or talus fractures, and foot deformities such as a varus or valgus heel, which increase tibial nerve pressure.
Among some of the uncommon causes of the condition are mass lesions in the tarsal tunnel such as ganglion, lipoma, venous varicosities or synovitis caused by rheumatoid arthritis.
Although clinical symptoms vary and depend on the site of compression, patients often experience a burning sensation in the plantar aspect of the forefoot, with pain radiating either proximally or distally from the posteromedial ankle.
Intrinsic factors such as hyperpronation of the foot create tension on the plantar fascia, which in turn, creates tension of the retinaculum, decreasing compartment volume of the tarsal tunnel and causing pain.
In their study published in the Foot & Ankle International, Trepman et. al. proved that eversion and inversion of the foot and ankle increased pressure in the tarsal tunnel, contributing to symptoms associated with entrapment of the posterior tibial nerve.
By obtaining the MRI of 13 ankles in nine healthy subjects in three positions (neutral, eversion, inversion), the authors observed that the mean tarsal tunnel volume was significantly greater when the foot and ankle were in neutral position than in either full eversion or inversion.
The findings of this study imply that the neutral immobilisation of the foot and ankle can help in the treatment and management of tarsal tunnel syndrome by reducing pressure on the posterior tibial nerve and maximising compartment volume of the tarsal tunnel.
For this purpose, using supportive devices for the feet prove to be a viable conservative treatment option; they help support the foot in its optimal posture and add strength to the intrinsic muscles of the foot which are responsible for the stabilisation of the medial longitudinal arch.
This reduces pressure on the plantar fascia and consequently, on the tibial nerve, helping decrease pain whilst realigning the musculoskeletal system to prevent the onset of any other such conditions in the future.
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Repetitive plantarflexion can lead to pain and mechanical limitation in the posterior ankle joint which is known as posterior ankle impingement syndrome. This pathology commonly occurs in ballet dancers and football players.