Nerve Injuries of the Lower Extremity

Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

1. Tarsal Tunnel Syndrome

Overview

• One of the most common nerve injuries in the lower extremity.

• Approximately 80% of cases have no identifiable cause.

• Involves compression of the posterior tibial nerve.

Symptoms

• Burning sensation

• Numbness

• Tingling

• Electric shock–like pain

• Symptoms occur on the plantar (bottom) aspect of the foot

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Persistent Symptoms After Surgery

• If symptoms persist six months after surgery:

  • Likely cause is incomplete release of impinging structures.

• Recurrence is usually due to:

  • Inadequate decompression.

• Repeat surgery is generally not advisable.

• Surgical decompression is not as predictably successful as carpal tunnel release.

• Outcomes are better when the cause is a ganglion compared to other causes.

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Anatomy Behind the Medial Malleolus (“Tom, Dick, and Harry”)

Structures passing behind the medial malleolus:

• Tom – Tibialis posterior

• Dick – Flexor digitorum longus

• Posterior tibial artery

• Posterior tibial vein

• Nerve – Posterior tibial nerve

• Harry – Flexor hallucis longus (important muscle of the foot)

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2. L5 Nerve Root

• Supplies extension of the big toe.

• Extensor hallucis longus is supplied by the L5 nerve root.

• Should not be confused with flexor hallucis longus.

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3. Cutaneous Innervation of the Foot

Plantar Surface

• Medial plantar nerve

• Lateral plantar nerve

• Sural nerve (lateral side)

• Saphenous nerve (medial side)

Important distinctions:

• Medial side of the foot ? Saphenous nerve

• Lateral side ? Sural nerve

• Medial plantar nerve and lateral plantar nerve supply the plantar surface.

Cutaneous innervation differs from the dorsum (top) of the foot.

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4. Lumbar Disc Herniation and Sensory Changes

Posterolateral L5–S1 Disc Herniation

• Decreases sensation over the lateral aspect of the foot.

• Corresponds to S1 distribution.

Foraminal L5–S1 Disc Herniation

• Affects the L5 nerve root.

• Decreases sensation over the dorsum (top) of the foot.

Sensory Summary

• Top of the foot ? L5

• Lateral side of the foot ? S1

• Medial side of the foot ? L4

• L5 sensory area on the dorsum corresponds to the superficial peroneal nerve distribution.

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5. Sciatic Nerve Injury

Clinical Presentation

• A high sciatic nerve lesion can mimic common peroneal nerve injury at the fibular head.

• Both conditions may present with foot drop.

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Differentiating Lesion Level

• Short head of the biceps femoris:

  • Supplied by the common peroneal branch of the sciatic nerve.

• Long head of the biceps femoris:

  • Supplied by the tibial branch of the sciatic nerve.

Role of EMG

• EMG of the short head of the biceps femoris helps determine lesion location.

If EMG abnormal in short head:

• Lesion is high (sciatic nerve level).

If EMG normal in short head:

• Lesion is distal (common peroneal nerve at the fibular head).

This is an important examination point.

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6. Deep Peroneal Nerve

• Provides sensory supply to the first web space (between the first and second toes).

• Superficial peroneal nerve supplies:

  • The remainder of the dorsum of the foot except the first web space.

Clinical relevance:

• First web space sensation can be tested in anterior compartment syndrome, which most commonly affects the anterior compartment.

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7. Lateral Plantar Nerve

• Branch of the posterior tibial nerve.

• Posterior tibial nerve arises from the tibial nerve.

• Tibial nerve is a branch of the sciatic nerve.

Importance

• Similar in function to the ulnar nerve in the hand.

• Supplies most of the intrinsic muscles of the foot.

• Supplies the interossei muscles.

• Frequently tested in examinations.

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Baxter’s Nerve

• First branch of the lateral plantar nerve.

• Can be confused with plantar fasciitis.

• Involved in chronic heel pain.

• Contributes to approximately 20% of heel pain cases.

• Supplies the abductor digiti muscle.

• May be injured during procedures involving insertion of a rod from the heel into the calcaneus and tibia.

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8. Heel Pain

• Multiple causes located within a small anatomical area.

• Structures are close to each other, making diagnosis difficult.

• Common causes include:

  • Plantar fasciitis

  • Baxter’s nerve involvement

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9. Interdigital Neuroma (Morton’s Neuroma)

Definition

• Compression of the interdigital nerve.

Location

• Approximately 80% occur in the third interdigital space.

• About 20% occur in the second interdigital space.

Symptoms

• Localized plantar forefoot pain

• Pain does not involve the entire foot.

• Pain radiates distally in approximately 60% of cases.

• Numbness occurs in approximately 40% of cases.

Examination Findings

• Focal, localized tenderness in the plantar web space.

• Tenderness is on the bottom (plantar side), not over the joint or dorsum.