Definition
· The most common compression neuropathy affecting the foot and ankle
· Leads to pain and paresthesia of the plantar foot
Anatomy
· The flexor retinaculum bridges the leg fascia proximally and the fascia of abductor pollicis distally
· Posterior tarsal tunnel
o Flexor retinaculum, calcaneus (medial), talus (medial), abductor hallucis (inferior)
o Contents: tibial nerve, posterior tibial artery, FHL, FDL, tibialis posterior
· Anterior tarsal tunnel
o Flattened surface defined by inferior extensor retinaculum and fascia overlying talus and navicula
o Contents: deep peroneal nerve, peroneus tertius, EHL, EDL, dorsalis pedis a.
· The posterior tibial nerve has 3 terminal branches
o Medial plantar
o Lateral plantar
o Medial calcaneal
· These 3 nerves most commonly branch within the tarsal tunnel
· Medial & lateral plantar nerves travel in their own fibrous tunnel distal to tarsal tunnel
· Distal TTS: compression of the first branch of the lateral plantar nerve
Etiology
· Intrinsic
o Masses (ganglion cysts, lipoma, neurilemmoma, varicous vein)
o Tenosynovitis of the tendons in tarsal tunnel
o Perineural fibrosis & osteophytes
· Extrinsic
o Biomechanical malalignment of the foot and ankle
o Soft tissue and osseous trauma
o Iatrogenic injury to lateral plantar nerve
§ Can occur during procedures on the plantar surface of the hindfoot
§ Particularly at risk during retrograde insertion of arthrodesis nail
Evaluation
· Pain is characterized as burning and paresthesias
· May present as a part of the “heel pain triad”
o Posterior tibial tendon deficiency, plantar fasciitis, tarsal tunnel syndrome
o due to loss of static and dynamic stabilizers of the medial arch and susequent traction neuropathy
· Aggrevated by walking, prolonged standing, running
· Usually radiates distally and proximally
· Positive Tinnel sign along the distribution of the tibial nerve
· Motor and sensory examinations are usually normal
· Pressure within the tarsal tunnel increases with ankle dorsiflexion and foot eversion – may be used as a diagnostic tool to reproduce symptoms
· Electrodiagnostic studies are accurate in 80-90% of patients
o Sensory nerve conduction tests are more likely to be abnormal than motor nerve conduction velocity tests
o More useful in diagnosing proximal causes of nerve entrapment
o Needle electromyography is questionable
Imaging
· Weight bearing radiographs to see any anatomical disruption
· MRI is useful to detect space occupying masses and synovitis
· CT may help in cases of osseous impingement
Treatment
· Non-surgical
o NSAIDs, local corticosteroid injections and immobilization are used to reduce inflammation in the tarsal tunnel
o Immobilization in a removable boot or cast is recommended after steroid injections to prevent iatrogenic tibialis posterior tendon rüptüre
o Custom orthoses may be beneficial if malalignment is present
· Surgical
o After 3-6 months of failed conservative management
o Procedure
§ Successful outcomes in 50-90% of patients
§ The tibial nerve should be identified proximal to the tarsal tunnel and decompressed including release of flexor retinaculum
§ Medial and lateral plantar nerves and medial calcaneal nerve should be decompressed
§ Distal tarsal tunnel release is indicated if the patient has chronic plantar medial heel pain
§ The first branch of the lateral plantar n. (Baxter n.) should be decompressed by releasing the deep fascia of abductor hallucis
§ Wrapping the nerve with autologous veins may prevent scarring
o The best results are seen in patients with:
§ Symptoms in distribution of the tibial nerve
§ Positive tinnel sign
§ Positive electrodiagnostic studies
§ Space occupying masses
o Suboptimal results
§ Double crush syndrome
§ Inadequate release
§ Postoperative hematome formation
§ Scarring around the nerve
§ Improper diagnosis