Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

Featured on Channel NewsAsia

Tarsal Tunnel Syndrome

Basics
Description
  • Tarsal tunnel syndrome is entrapment of the tibial nerve or its distal branches caused by compression or traction as the nerve courses through the tarsal tunnel.
  • Anatomy :
    • Proximal tarsal tunnel:
      • Fibro-osseous space that contains (from anterior to posterior) the PTT, flexor digitorum longus tendon, posterior tibial artery and vein, tibial nerve, and flexor hallucis longus tendon.
      • The tarsal tunnel is a continuation of the deep posterior compartment of the leg.
      • The floor is composed of the medial surface of talus, the sustentaculum tali, and the medial wall of the calcaneus.
      • The roof is composed of the flexor retinaculum, which begins up to 10 cm proximal to the medial malleolus; each tendon and the neurovascular bundle is contained by separate fibro-osseous compartments that connect with the retinaculum.
    • The tibial nerve gives rise to the MCN, MPN, and LPN; nerve anatomy can be variable.
      • MCN:
        • 69-90% of the time, arises directly from the tibial nerve
        • Also can arise from the LPN
        • Single nerve branch in 79%, but can be multiple branches
        • Provides sensation to medial heel
      • MPN and LPN:
        • Formed by terminal bifurcation of tibial nerve
        • 93-96% of the time, bifurcation takes place within the tarsal tunnel.
        • Remainder occurs proximal to tarsal tunnel, in the leg.
      • MPN:
        • Provides sensation to plantar foot, big toe, 2nd toe, 3rd toe, and medial border of the 4th toe
        • Provides motor innervation to the abductor hallucis, flexor digitorum brevis, flexor hallucis brevis, and 1st lumbrical
      • LPN:
        • Provides sensation to lateral border of the 4th toe and to the 5th toe
        • Provides motor innervation to the quadratus plantae, abductor digiti minimi, flexor digiti minimi brevis, lateral 3 lumbricals, adductor hallucis, and the interossei
        • Most common nerve involved in tarsal tunnel syndrome
        • The distal tarsal tunnel begins as the MPN and LPN pass through separate fibrous tunnels deep to abductor hallucis.
      • MPN may be trapped between the navicular and the abductor hallucis, or at the knot of Henry.
      • The 1st branch of the LPN may be trapped in fascia of abductor hallucis as it travels to abductor digiti quinti, causing heel pain.
Pregnancy Considerations
  • Tarsal tunnel syndrome can occur during pregnancy, typically secondary to local compression caused by fluid retention and volume changes.
  • Care usually is supportive until after delivery, because many cases resolve after pregnancy.
Epidemiology
  • In a literature review of 186 cases, patients ranged from 14-80 years old .
  • Slightly more common in females (56%) than in males
Incidence
Unknown
Risk Factors
  • No clear risk factors have been proven, but several authors have associated tarsal tunnel syndrome with certain occupations and activities.
    • Jogger’s foot: Excessive hindfoot valgus is theorized to stretch the tibial nerve during repetitive activity such as running .
    • Activities that consist of repetitive squatting or crouching, such as in race jockeys
Pathophysiology
  • Tarsal tunnel syndrome is caused by compression or tension on the tibial nerve, resulting in damage .
  • Unyielding structure of tarsal tunnel places nerve at risk for injury from local volume changes.
  • Compressive etiologies: Sensory abnormalities are hypothesized to result from nerve ischemia, whereas late motor dysfunction may be the result of direct nerve compression injury.
  • Chronic traction injuries produce fibrosis of the epineurium and stiffness, which makes the nerve less able to compensate for other insults.
Etiology
  • The specific cause is identifiable in only 60-80% of patients ; causes can be grouped into 3 categories: Trauma, space-occupying lesion, and deformity.
  • Most common causes:
    • Trauma: 17%
    • Varicosities: 13%
    • Hindfoot varus: 11%
    • Fibrosis: 9%
    • Hindfoot valgus: 8%
  • Other causes of compression include ganglia, lipoma, neurilemmoma, inflammatory synovitis, PVNS, tarsal coalition, and accessory musculature.
Diagnosis
Signs and Symptoms
Frequently misdiagnosed because of poorly localized and variable symptoms
History
  • Insidious/intermittent onset of pain and paresthesias
  • Location of symptoms defined by the nerves involved
  • Neurogenic pain (burning, paresthesias, numbness)
  • Pain can radiate proximally up the medial leg (Valleix phenomenon) in 33% of patients with severe compression, or distally along path of involved nerves .
  • Pain usually worse with standing or activity
  • Some patients have substantial night pain, which may be related to venostasis.
  • Symptoms improve with rest, loose shoe wear, and elevation.
Physical Exam
  • Perform a complete foot and ankle examination.
  • Foot alignment:
    • Examine for hindfoot varus or valgus abnormalities.
    • Exaggerating heel dorsiflexion, inversion, or eversion may reproduce symptoms by stretching or compressing the nerve.
  • Palpate the tarsal tunnel and course of the tibial nerve for:
    • Tenderness
    • Swelling consistent with a space-occupying lesion
  • Tinel sign: Percussion over the course of the tibial nerve may produce paresthesias and distal symptoms.
  • Cuff test: Using a pneumatic cuff to create a venous tourniquet may cause engorgement of varicosities and reproduce symptoms.
  • Compression test: Applying pressure to tarsal tunnel for 60 seconds may reproduce symptoms.
  • Sensory examination:
    • The MCN usually is spared, but numbness and altered sensation may be present in the distribution of the MPN or LPN.
    • 2-point discrimination is decreased early in the disease process.
  • Motor examination:
    • Intrinsic weakness is difficult to assess.
    • Rarely, weakness of toe plantarflexion may be noted.
    • Atrophy of the abductor hallucis or abductor digiti minimi may be seen late in the disease process.

Tests
Lab
Routine laboratory tests can be used to rule out other conditions that may mimic tarsal tunnel syndrome, including peripheral neuropathy caused by diabetes or other systemic illnesses.
Imaging
  • Routine weightbearing radiographs to assess for fracture or exostoses
  • MRI:
    • Can be helpful in assessing the tarsal tunnel for masses or other sources of nerve compression before surgery
    • In 1 study, a causative agent was identified in 88% of symptomatic feet.
Pediatric Considerations
MRI is recommended for evaluating pediatric tarsal tunnel syndrome because compression by a neoplastic mass is not uncommon.
Diagnostic Procedures/Surgery
  • Electrodiagnostic studies:
    • Can evaluate for evidence of underlying peripheral neuropathy
    • Isolated motor latencies have a lower sensitivity than sensory or mixed action potentials.
    • Sensory action potentials are the most sensitive test (90.5%), but they also have the highest false-positive rate (8%).
    • Mixed motor and sensory conduction velocities are abnormal in 85.7%, with a very low false-positive rate.
    • It is important to evaluate for proximal nerve compression, including a lumbar radiculopathy or a double-crush phenomenon.
Pathological Findings
  • At the time of surgical exploration, the following may be found:
    • Focal swelling, scarring, or nerve abnormalities
    • A pathologic source of compression
Differential Diagnosis
  • Peripheral neuropathy (diabetes)
  • Peripheral neuritis
  • Peripheral vascular disease
  • Morton neuroma
  • Metatarsalgia
  • Subtalar joint arthritis
  • Tibialis posterior tendinitis/dysfunction
  • Plantar fasciitis
  • Complex regional pain syndrome
  • Proximal injury or compression of the tibial branch of the sciatic nerve
  • Lumbar radiculopathy
Treatment
General Measures
  • Initially, nonoperative management is recommended except for acute tarsal tunnel syndrome or in the setting of a known space-occupying lesion (excluding synovitis) .
    • Rest/immobilization
    • Orthotics
    • Anti-inflammatories, including steroid injections and nonsteroidal drugs
    • Medications that alter neurogenic pain (tricyclic antidepressants, antiepileptic drugs, nerve blocks)
    • Physical therapy (desensitization)
    • Compression stockings
    • Weight loss
Surgery
  • Surgery is indicated:
    • If nonoperative measures fail after a 3-6-month trial
    • In the setting of acute tarsal tunnel syndrome
    • If the cause is a space-occupying lesion
  • Use a curved posteromedial incision, following the course of the tibial nerve.
  • Release the entire flexor retinaculum.
  • Release the MPN and LPN distally as they pass deep to the abductor hallucis and into the plantar foot.
  • Excise space-occupying lesions and address underlying pathology such as tendon dysfunction and tarsal coalition.
  • Minimize surgical dissection to help limit scar formation.
Follow-up
  • Postoperative management includes:
    • Nonweightbearing splint until incision heals (2-3 weeks), followed by progressively increased weightbearing and ROM exercises.
    • RICE protocol to limit swelling
Prognosis
  • Best results are seen in young patients, when surgery is performed early in the disease process (before motor abnormalities occur) or when a discrete lesion is found.
  • In a review of 25 articles, 91% of 110 patients had improvement or resolution of symptoms with surgery.
  • A more recent study with longer patient follow-up and more stringent criteria has shown poorer outcomes, with deteriorating results over time .
Complications
  • The main adverse outcome is unsuccessful surgical intervention: No improvement, partial/incomplete improvement, or temporary improvement with recurrence of symptoms .
  • 5 causes of failed tarsal tunnel release:
    • Incorrect diagnosis
    • Incomplete release
    • Adhesive neuritis (external scar formation)
    • Intraneural damage (systemic disease, direct nerve injury)
    • Failure to treat all sources of nerve compression in a double-crush phenomenon
  • Examination of the incision length is the most important part of the physical examination in determining whether an adequate release was done initially.
  • Electrodiagnostic studies are not helpful for diagnosing tarsal tunnel syndrome after a failed release.
  • Repeat surgical release, combined with a barrier procedure (vein or synthetic graft wrapping around the nerve), is the operative treatment of choice for adhesive neuritis.
  • Results for revision surgery are poorer than those for primary surgical release.

Miscellaneous
Codes
ICD9-CM
355.5 Tarsal tunnel syndrome
Patient Teaching
The patient should be actively involved in the decision-making process, with a clear understanding of the risks and benefits of surgical and nonsurgical treatments.

FAQ

Q: Electrodiagnostic studies for tarsal tunnel syndrome can also rule out what important conditions included in the differential diagnosis?
A: Peripheral neuropathy and lumbar radiculopathy.
Q: What is the recommended treatment for acute tarsal tunnel syndrome, such as occurs with calcaneal or talar fracture?
A: Acute tarsal tunnel syndrome from trauma is caused by displaced fracture fragments, tension on the nerve structures, or compression by hematoma. Acute surgical decompression of the tarsal tunnel is combined with fracture reduction and fixation to relieve pressure on the tibial nerve.

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