Tarsal Tunnel Syndrome

Tarsal tunnel syndrome (TTS), otherwise known as tibial nerve dysfunction or posterior tibial nerve neuralgia, is a compressive neuropathy of the foot caused by entrapment of the tibial nerve as it passes through the tarsal tunnel. The tarsal tunnel is an osteofibrous canal that allows tendons, nerves, and blood vessels to travel between the posterior leg and the foot. 

Tarsal tunnel syndrome is similar to carpal tunnel syndrome, a nerve entrapment disorder caused by compression of the median nerve as it runs through the carpal tunnel of the wrist. 

Tarsal tunnel syndrome is caused by posterior tibial nerve compression as it travels through the tarsal tunnel. At the ankle, the tibial nerve passes posteriorly and inferiorly to the medial malleolus through a narrow structure known as the tarsal tunnel. This tunnel is covered by a thick ligament called flexor retinaculum that protects the structures within the canal. Immediately distal to the tarsal tunnel, the tibial nerve terminates by dividing into sensory branches, which innervate the sole and motor branches, which supply the intrinsic foot muscles.

Any tibial nerve compression at the tarsal tunnel can lead to tarsal tunnel syndrome. Ankle fractures and sprains can cause injury at the tarsal tunnel; foot deformities (e.g., flat feet, varus or valgus deformity of the foot); bone spurs; or external pressure to the ankle, such as with tight shoes or a cast. The tibial nerve can also become entrapped or compressed within the tarsal tunnel due to space-occupying lesions (e.g., ganglion cysts, lipomas, tumors, varicose veins);  or enlargement of other structures passing through the tarsal tunnel, such as with tendonitis of the flexor tendons or hypertrophy of the flexor retinaculum. 

Signs and symptoms of tarsal tunnel syndrome include shooting pain, numbness, and tingling over the sole, which is the area of skin innervated by the tibial nerve. Symptoms are often aggravated by activity (e.g., prolonged standing, walking, exercise) and tend to worsen at night. In severe cases, motor function may also be affected, causing weakness and wasting intrinsic foot muscles. Plantar flexion and foot inversion generally remain intact when injury of the tibial nerve occurs at the tarsal tunnel, as the innervation to the lower leg muscles is not affected.

Diagnosis of tarsal tunnel syndrome utilizes the findings of the history and physical examination with those of nerve conduction studies and diagnostic imaging tests. Upon physical examination, symptoms of tarsal tunnel syndrome may be reproduced when tapping the tibial nerve, a finding known as a positive Tinel sign. Nerve conduction studies may help to detect compression of the tibial nerve. Electromyography typically demonstrates abnormal activity within the intrinsic foot muscles, though normal findings do not rule out compression as there can be false negatives. Finally, diagnostic imaging techniques, such as ultrasound or magnetic resonance imaging (MRI), may be done to identify the cause of compression and assist with surgical planning.

Treatment of tarsal tunnel syndrome can be either non-surgical or surgical, depending on the cause of compression and the degree of symptoms. Conservative treatments include rest; applying ice; pain-relief medications (e.g., acetaminophen, non-steroidal anti-inflammatory drugs); and physical and rehabilitation therapy. 

In cases where initial treatment does not improve the symptoms, corticosteroid injections may be performed to decrease inflammation. Surgical treatment is often considered in cases with an apparent cause of nerve entrapment and the failure of conservative treatment. Surgical decompression involves releasing the flexor retinaculum to eliminate compression of the tibial nerve. 

Tarsal tunnel syndrome (TTS) is a nerve entrapment disorder that results from compression of the posterior tibial nerve as it passes through the tarsal tunnel. Symptoms of TTS include shooting pain, numbness, and tingling over the sole. Diagnosis is based on history and physical examination; however, nerve conduction studies and imaging techniques may be conducted to aid in the diagnosis. Treatment of TTS may include conservative measures, such as rest, ice, pain-relief medications, and physical therapy. In cases where conservative management fails, surgical decompression may be performed.