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Tarsal tunnel syndrome (TTS), also known as posterior tibial neuralgia, is a compression neuropathy and painful foot condition. It occurs when tibial nerve is compressed as it travels through the tarsal tunnel of the foot/ankle.

The Anatomy

The posterior tibial nerve travels down the back of the leg and around to the medial side of the ankle (big toe side). It then runs behind the big bony prominence on the medial side of the ankle known as the medial malleolus

Just behind the medial malleolus is the posterior tibial tendon, then the flexor digitorum longus tendon, and finally the posterior tibial artery. Nerves and several veins also run through this part of the body. 

Covering the tendons, arteries and nerves is a sheet of tissue called the flexor retinaculum. And the space underneath the flexor retinaculum, at the level of the ankle, is known as the tarsal tunnel.

The posterior tibial nerve splits at the level of the tarsal tunnel into the medial plantar nerve and the lateral plantar nerve. The tendons, arteries and nerves all travel around the side of the ankle into the bottom (plantar) aspect of the foot. 

The medial plantar nerve supplies sensation to the medial side of the sole of the foot, as well as sensation to the first, second and third toe. The lateral plantar nerve supplies sensation to the lateral (outer) part of the sole, and as well as the fourth and fifth toe. 

A small branch called the medial calcaneal nerve comes off the posterior tibial nerve inside the tarsal tunnel, running to the medial side of the heel and supplying sensation to the medial or inner side of the heel.

The Symptoms

Any condition that produces increased pressure or inflammation in the tarsal tunnel may cause irritation or compression neuropathy of the posterior tibial nerve. This is known as Tarsal Tunnel Syndrome. Symptoms include:

  • numbness on the sole or plantar aspect of the foot
  • tingling, burning or pain
  • weakness or atrophy of the intrinsic muscles
  • a claw toe deformity of the toes may develop secondary to this weakness in severe cases

The Diagnosis

A diagnosis of this condition is made by:

  • obtaining a history of the above symptoms
  • recreating numbness or tingling on the plantar side of the foot via a positive Tinel's test
  • observing possible atrophy of the intrinsic muscles
  • testing nerve function via electrodiagnostic tests such as nerve conduction velocity (NCV) or electromyography (EMG) 

The Causes

Several causes of tarsal tunnel syndrome exist. Inflammation and swelling of the tendons may result from:

  • certain lifestyle habits and overuse activities
  • the presence of pre-existing inflammatory conditions, such as rheumatoid arthritis or lupus
  • repetitive stretching or tension on the nerve (which may occur in patients with flat feet with increased pronation)
  • synovitis (or inflammation synovial membrane) or irritation of the underlying ankle joint or subtalar joint (both may produce pressure upward on the tarsal tunnel)
  • a ganglion cyst (which can sometimes grow into the tarsal tunnel)
  • swelling of the collection of veins or venous plexus around the nerve (which produce increased pressure on the nerve with standing and weight-bearing)

The Treatment

Treatment of tarsal tunnel syndrome may initially be conservative. Anti-inflammatories are used to reduce inflammation, and arch supports and orthotics can reduce pronation in patients with flat feet. 

In severe cases or when conservative treatment fails, surgery may be required. During surgery, a curved incision is made on the medial side of the ankle over top of the tarsal tunnel. The flexor retinaculum over top of the tarsal tunnel is split, opening up the tarsal tunnel and relieving pressure. Any mass in the tarsal tunnel is removed. A swollen venous plexus is split and cauterized, reducing pressure on the nerve. The nerve is freed, down to the foot. The skin is then closed and a dressing and boot are applied. 

There is no weight-bearing allowed for 6 weeks post-op. During therapy, the boot is removed and early range of motion exercises of the ankle and foot begun. This allows the nerve to mobilize and reduce scarring. 

Results of surgery are approximately 75% successful in major studies.

Risks with this condition and surgery include anesthesia-related risks, wound healing problems, potential infection, continued irritation of the nerve, and the development of a condition called reflex sympathetic dystrophy (resulting in stiffness and pain of the foot).