Virtual Fellowship 2025

Nerve entrapment syndromes in the foot and ankle are conditions where a peripheral nerve is compressed, typically within a fibro-osseous tunnel or by surrounding anatomical structures, leading to pain, numbness, and/or weakness. These conditions are often under-diagnosed or misdiagnosed as other musculoskeletal issues.
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General Discussion Points [edit]

• Anatomy and Vulnerability:

  • "Tunnel Syndromes": Discuss the concept of a nerve being compressed within confined anatomical spaces (e.g., the tarsal tunnel), which is analogous to Carpal Tunnel Syndrome in the wrist.

  • Superficial Location: Emphasize that several nerves (like the Common Peroneal and Sural nerves) are superficial at key points, making them vulnerable to external compression from casts, tight footwear, or direct trauma.

• Clinical Presentation and Diagnosis:

  • Classic Symptoms: Review the triad of symptoms: pain (often burning or shooting), paresthesia (tingling or "pins and needles"), and numbness in the nerve's distribution.

  • Motor Involvement: Discuss that motor nerve involvement can lead to muscle weakness and, in chronic cases, atrophy (muscle wasting), resulting in functional deficits like foot drop.

  • Provocative Tests: Highlight the importance of the Tinel's Sign (percussion over the suspected entrapment site reproduces symptoms) and specific provocative maneuvers (e.g., stretching the nerve).

  • Diagnostic Tools: Discuss the role and limitations of Electromyoneurography (EMG/NCS)—it can confirm nerve damage but has a high false-negative rate for some distal entrapments. Also, consider Ultrasound and MRI to identify space-occupying lesions or nerve swelling.

  • Differential Diagnosis: Stress the need to rule out other conditions with similar symptoms, such as lumbar radiculopathy (pinched nerve in the back), peripheral neuropathy (e.g., from diabetes), or simple musculoskeletal issues like plantar fasciitis (which is often confused with distal tibial nerve branch entrapment).

• Treatment Principles:

  • Conservative Management: Focus on reducing inflammation (NSAIDs, ice, rest), modifying activity, and addressing biomechanical causes (orthotics, physical therapy).

  • Injections: Discuss the use of corticosteroid injections for short-term relief, noting that repeated injections carry risks (e.g., tendon rupture). They also serve a diagnostic purpose.

  • Surgical Decompression: When conservative measures fail, surgical neurolysis and decompression are considered to physically free the nerve from compression. Outcomes are generally better when a clear, treatable cause (e.g., ganglion cyst) is identified.

Specific Entrapment Syndromes [edit]

1. Tarsal Tunnel Syndrome (TTS) and Distal Branches

Tarsal Tunnel Syndrome is the entrapment of the Posterior Tibial Nerve (PTN) or its branches as they pass through the tarsal tunnel behind the medial malleolus (inner ankle bone).

• Anatomy: The tarsal tunnel is bounded by bone (medial malleolus, talus, calcaneus) and the flexor retinaculum (a thick fibrous band). It contains the PTN, posterior tibial artery/vein, and tendons of the deep posterior compartment (Tom, Dick, and Harry: Tibialis posterior, Flexor Digitorum Longus, Flexor Hallucis Longus).

• Aetiology (Causes): Often idiopathic (no clear cause), but common factors include trauma (ankle sprains, fractures), space-occupying lesions (ganglia, varicose veins, tenosynovitis), and biomechanical factors (e.g., severe pes planus/flatfoot causing increased tension).

• Symptoms: Pain, burning, and tingling typically in the sole (plantar aspect) of the foot, which can worsen with activity and often at night. Symptoms can radiate proximally into the calf (Valleix phenomenon).

• Distal Branches:

  • Medial Plantar Nerve Entrapment ("Jogger's Foot"): Pain along the medial arch and possibly into the first 3 toes. Often confused with plantar fasciitis.

  • Lateral Plantar Nerve Branch Entrapment (Baxter's Nerve): Compression of the first branch of the lateral plantar nerve near the heel. Causes chronic, severe heel pain that can mimic plantar fasciitis.

2. Common Peroneal Nerve Entrapment

The Common Peroneal (Fibular) Nerve is a branch of the sciatic nerve that is most commonly compressed where it wraps superficially around the head of the fibula (near the knee).

• Vulnerability: The nerve's superficial course at the fibular head makes it highly susceptible to external compression (e.g., habitual leg crossing, tight casts, prolonged bed rest, direct trauma).

• Symptoms: Entrapment often results in foot drop (inability to actively lift the ankle and toes, or dorsiflexion), leading to a characteristic steppage gait (lifting the knee high to clear the foot).

• Sensory Loss: Numbness and tingling typically occur over the lateral leg and the dorsum (top) of the foot.

• Differentiation: It's crucial to differentiate this peripheral entrapment from a more central lesion (e.g., L5 lumbar radiculopathy), which can present with similar motor/sensory deficits.

3. Deep Peroneal Nerve Entrapment (Anterior Tarsal Tunnel Syndrome)

This is a rarer entrapment of the Deep Peroneal Nerve (DPN) as it passes under the inferior extensor retinaculum on the front of the ankle and foot.

• Anatomy: The nerve runs in the anterior compartment of the leg, crossing the front of the ankle.

• Aetiology: Often caused by trauma, tight ski boots/footwear, or the presence of a dorsal osteophyte (bone spur) on the ankle joint, creating a tight space.

• Symptoms: Pain and paresthesia typically localized to the first dorsal webspace (between the great toe and the second toe). Pain on the dorsum of the foot that is aggravated by forced plantarflexion (pointing the toes down), which stretches the nerve.

• Motor: Weakness of the toe extensors (especially Extensor Digitorum Brevis) can be a sign in more severe cases.

4. Others

• Superficial Peroneal Nerve (SPN) Entrapment:

  • Entrapment Site: As the nerve exits the deep fascia of the lateral compartment, typically in the middle or lower leg.

  • Symptoms: Sensory symptoms (pain, burning, numbness) over the lateral lower leg and dorsum of the foot(sparing the first webspace). Often seen after ankle sprains, trauma, or with fascial defects.

• Sural Nerve Entrapment:

  • Entrapment Site: Commonly compressed behind the lateral malleolus (outer ankle bone) or along its course in the calf/lateral foot.

  • Symptoms: Sensory symptoms over the lateral ankle and lateral/outer border of the foot. Frequently affected by ankle sprains, scarring from surgery, or tight shoe straps. Often misdiagnosed as Achilles tendinopathy.

• Saphenous Nerve (Infrapatellar Branch) Entrapment:

  • The saphenous nerve is a pure sensory nerve. While entrapment is more common around the knee, its infrapatellar branch can be irritated or entrapped, causing symptoms on the medial side of the knee and upper shin/calf.