Tarsal Tunnel Syndrome is a compression neuropathy caused by the compression of the posterior tibial nerve within the tarsal tunnel. It is similar to the compression of the medial nerve of the wrist which causes carpal tunnel syndrome. Tarsal Tunnel Syndrome is the most common compression neuropathy in the ankle and foot. The tarsal tunnel is a fibro-osseous tunnel posterior and inferior to the medial malleolus (Figure 1). The tunnel is covered by the flexor retinaculum, which protects the structures contained within the tunnel. The flexor retinaculum is a thick ligament that runs between the medial malleolus and the calcaneus. The structures which pass through the tunnel include the Tibialis posterior, the flexor digitorum longus, the posterior tibial artery, the tibial nerve, and the flexor Hallucis longus. The mnemonic device used to remember these structures is “Tom, Dick, and Harry” (Figure 2).
Thickening of the flexor retinaculum may cause compression of the posterior tibial nerve. 80% of the cases are associated with a specific cause. The causes are many and include: Space occupying lesions such as a Lipoma or ganglia, varicose veins, muscle anomalies, history of trauma, tenosynovitis, rheumatoid arthritis, diabetes, and foot malalignments.
Symptoms of Tarsal Tunnel syndrome include: burning pain, numbness, tingling, and an electric shock sensation which will typically occur around the ankle or at the bottom of the foot (the plantar aspect of the foot). Additionally, there may be swelling around the ankle and foot (Figure 3). Symptoms will worsen with activity—such as walking, standing, or running and be relieved with rest and elevation. Pain associated with tarsal tunnel syndrome may be worse at night.
During the physical exam, you will find the patient has a positive compression test and a positive Tinel’s sign. Tapping on the nerve posterior to the medial malleolus causes radiating pain into the medial side of the ankle and possibly to the foot. Pressure within the tarsal tunnel increases with ankle dorsiflexion and foot eversion—this may reproduce the symptoms. Pain associated with tarsal tunnel syndrome radiates proximally and distally. Tarsal tunnel syndrome may be present as part of the heel pain triad which occurs in adults. The heel pain triad includes tarsal tunnel syndrome, plantar fasciitis, and acquired flat foot deformity. A flat foot deformity will increase tension of the nerve (Figure 4).
An EMG or other nerve studies may be helpful. A combination of history, examination, EMG, and nerve studies can lead you to the diagnosis (history is the most useful examination, EMG is accurate in about 80-90% of the time). Sensory nerve conduction studies are more helpful than motor studies (EMG). Always rule out radiculopathy from irritation of the spinal nerve root or disc herniation. Radiographs and CT scans may show osseous impingement or a fracture of the talus. An MRI may show a space occupying lesion such as a ganglion cyst or lipoma.
Differential diagnosis includes Peripheral Neuropathy, which involves all the nerves of the foot—not just the tibial nerve. You will see that the sural nerve and saphenous nerve are also involved and there will be an absent ankle jerk.
Treatment for tarsal tunnel syndrome includes: Immobilization, anti-inflammatory medications, and steroid injections. The patient may have an orthotic with medial posting if the patient has a valgus hindfoot. A surgical release (Figure 5) of the tarsal tunnel will be performed if nonoperative treatment fails after a trial of 3-6 months. The surgeon will release the fascia proximal to the flexor retinaculum, the flexor retinaculum, and the tibial nerve will be located proximal to the tunnel and its three branches will be released. You will need to decompress the entire tunnel 5cm proximal to the flexor retinaculum and distally to the deep fascia of the abductor hallucis. Distal release of the Baxter’s nerve (Figure 6) is usually done if the patient has chronic plantar medial heel pain (heel pain is uncommon in tarsal tunnel). The Baxter’s nerve is decompressed by releasing the deep fascia of the Abductor Hallucis and removing any space occupying mass.
Best results will occur if symptoms have occurred for less than one year. A successful outcome occurs in about 50-90% of cases. The best results occur if the patient has a space occupying lesion with a positive physical examination and EMG findings. The suboptimal result can occur from inadequate release, traction neuritis, and repeat tarsal tunnel release. In these situations, the patient will not respond well to surgery (always rule out double crush syndrome). Revision surgery has a less successful outcome unless the patient had an inadequate release. Although carpal tunnel release surgery usually generates a positive result, a tarsal tunnel decompression may not produce a good long-term outcome.