Foot Drop

Introduction

• Foot Drop is a gait abnormality where the forefoot drops due to weakness or paralysis of the dorsiflexor muscles.
• It is a multifactorial condition involving central, spinal, or peripheral nervous systems.
• Management varies from conservative treatment to surgery depending on the underlying cause.
• Why Important..? FD affects mobility, gait, and quality of life; presents across multiple orthopedic subspecialties.

 

Anatomy of Common Peroneal Nerve (CPN)

• CPN is a branch of The Sciatic Nerve, formed from L4–S2 roots.
• Travels posterolaterally around the fibular neck, dividing into superficial and deep branches.
• Innervates Tibialis Anterior, Extensor Hallucis Longus, Extensor Digitorum Longus, And Peroneal Muscles.
• Provides sensation to the anterolateral leg and dorsum of the foot.
• Injury-prone areas: Fibular neck, popliteal fossa

 

Common Fibular Nerve/ Common Peroneal Nerve

• Overview
  • Nerve Roots: L4, L5, S1, S2
  • Motor
    • Short head of Biceps Femoris
    • Anterior Compartment of the Leg
    • Lateral Compartment of the Leg
  • Sensory
    • Lateral leg, dorsal foot
  • Anatomic Course
    • Originates in the popliteal fossa, branching off the sciatic nerve
    • Follows the medial border of biceps femoris
    • Runs over the lateral head of gastrocnemius
      • Here the two cutaneous branches come off
    • The nerve then wraps around the neck of the fibula
    • It passes between the attachments of fibularis longus
    • Here the nerve terminates then divides into
      • Superficial Fibular Nerve
      • Deep Fibular Nerve
    • Motor Function
      • Short head of Biceps Femoris
      • Anterior Compartment of the Leg
        • Tibialis Anterior
        • Extensor Hallucis Longus
        • Extensor Digitorum Longus
        • Peroneus Tertius
      • Lateral Compartment of the Leg ; Fibularis Longus, Fibularis Brevis
    • Sensory Function
    • Sural Communicating Nerve
      • Combines with a branch of  tibial nerve to form sural nerve
      • Innervates the skin over the lower posterolateral leg
    • Lateral Sural Cutaneous Nerve
      • Innervates the skin over the upper lateral leg
    • Superficial Fibular Nerve
      • Innervates the skin of the anterolateral leg
      • Dorsum of the foot, except the first web space
    • Deep Fibular Nerve
      • Innervates the skin of the first web space

 

Pathophysiology of Peripheral Nerve Injury

• Nerves have three layers: epineurium, perineurium, endoneurium.
• Seddon’s classification:
  • Neurapraxia: Myelin damage, intact axon (good prognosis).
  • Axonotmesis: Axon damage with connective sheath preserved.
  • Neurotmesis:  Complete nerve transection (worst prognosis)
• Sunderland’s classification further stratifies axonotmesis.
• Regeneration involves
  • Wallerian Degeneration
  • Axonal Sprouting
• Prognosis depends on injury type, location & time to intervention

 

Gait Changes in FD

• High-stepping gait  (steppage gait) to avoid toe drag, due to inability to dorsiflex during swing phase.
• Swing phase compensation: Excessive hip and knee flexion and internal rotation during
• Stance phase adaptation: Ipsilateral hip hiking
• Long-term consequences: Achilles shortening, equinus deformity, contracture, Chronic strain on plantar flexors.
• Quality of life ; 69% require mobility aids.

 

Etiology Overview

• Multifactorial: Central, spinal, peripheral, systemic, iatrogenic causes or neuromuscular causes.
• Central causes
• Spinal causes
• Peripheral causes (most common)
• Double Crush Syndrome: Proximal nerve compression increases susceptibility to distal entrapment
• Other factors: Chemotherapy-induced neuropathy, neuromuscular & systemic diseases
• Peripheral CPN neuropathy is the most common cause.
• Accurate diagnosis is key to effective treatment planning.

 

Central Nervous System Causes

• Causes include strokes, tumors, cerebral palsy.
• Often part of global paresis; 14% of strokes result in residual FD.
• Tumors can cause FD via mass effect or edema.

 

Spinal and Intraspinal Causes

• Disk herniation at L4/L5 and L5/S1 often compresses nerve roots.
• Spinal AV fistulas and tumors can lead to cord compression.
• Iatrogenic causes: nerve injury during spine surgery.
• Most commonly affects the L5 nerve root.
• Cerebral palsy – involve spastic or flaccid forms of FD.

Peripheral Nerve Causes

• Compression or trauma at the fibular neck.
• Common in prolonged leg crossing, tight splints, lithotomy position.
• Seen in occupations requiring prolonged squatting (e.g., strawberry pickers).
• Weight loss reduces soft tissue padding, increasing nerve vulnerability.

 Iatrogenic and Traumatic Causes

• Surgery: THA, TKA, meniscus repairs can cause direct or traction injury.
• Trauma: knee dislocations, fibula fractures, gunshot wounds.
• Reperfusion injury following compartment syndrome can compress CPN.

Neuromuscular and Systemic Causes

• ALS, MS, muscular dystrophy, Charcot-Marie-Tooth disease.
• CIPN from drugs: platinum-based, taxanes, vinca alkaloids.
• Often bilateral and progressive.
• Must differentiate from localized CPN injury.

 

 Clinical Diagnosis

• Muscle strength testing: Dorsiflexion, Eversion, Toe Extension (TA, EHL, Peroneals).
• Gait analysis
• Reflexes preserved in CPN injury but altered in radiculopathy.
• Tinel’s Sign: Positive at fibular head, suggests local compression
• Straight leg raise for L5 involvement.
• Differentiate:
  • CPN vs. L5 radiculopathy
  • Sciatic nerve lesions
  • Plexopathies

 

Sensory Exam and Localization

• CPN sensory loss: distal lateral leg, dorsum of foot, first web space.
• Sciatic nerve involvement affects short head of biceps femoris.
• Posterior tibialis function can help localize lesion (tibial vs. CPN).
• Straight leg raise: Helps rule out spinal involvement
• Palpation for masses, thickening, or tenderness at fibular tunnel.

 

Electrodiagnostic Testing

• EMG and NCS are crucial for localization and prognosis.
• Differentiate between CPN, sciatic, and L5 lesions.
• Assess for axonal damage, conduction block, and reinnervation potential.
• Key muscles for testing: Tibialis anterior, biceps femoris (short head), posterior tibialis
• Prognosis varies depending on presence of axonal damage.

 

Imaging Modalities

• Radiographs: rule out bone lesions.
• Ultrasound: visualize ganglion cysts, nerve thickening and entrapment.
• MRI: Evaluates spine (for disc, tumor) or fibular tunnel lesions
• MRI neurography for peripheral nerve visualization (Evaluates spine (for disc, tumor) or fibular tunnel lesions).
• CT for evaluating structural causes or post-surgical issues.

Nonsurgical Management – General Approach

• Conservative care first: Observation, PT, Activity Modification.
• Activity Modification: Avoid leg crossing, prolonged pressure on fibular head
• Physical Therapy: Gait training, prevent contractures, improve strength
• AFOs (Ankle Foot Orthosis) support ankle in neutral position and prevent contracture.
  • Passive: Thermoplastics, carbon fiber for rigid support
  • Active: Dynamic ankle control, less muscle atrophy
  • Carbon fiber models for energy efficiency
  • Hinged AFOs allow limited motion.

 

Nonsurgical Management – Stimulation & Medication

• Functional Electrical Stimulation (FES): promotes muscle use.
• Transcutaneous Electrical Nerve Stimulation (TENS): pain relief.
• Botulinum toxin: used in spastic cases (e.g : cerebral palsy)
• NSAIDs, neuropathic pain medications may be helpful.

 

Surgical Management – Indications and Timing

• Indicated – Failure of conservative management, compressive lesions, trauma.
• Timing critical: Earlier surgery better for axonal injury.
• Wait 3–6 months if spontaneous recovery expected.
• Diagnostic confirmation via imaging and EMG needed pre-op.

 

Surgical Techniques – Nerve Focused

• Decompression of CPN at fibular tunnel.
• Nerve repair/grafting for acute transections
• Nerve grafts for defects > 6 cm.
• Nerve transfer (e.g., Tibial nerve to Deep PN) for large defects.
• Limited regeneration potential of CPN affects outcomes.

 

Surgical Techniques – Tendon Transfer and Spine

• Posterior tibialis transfer: restores dorsiflexion.
• “Bridle” procedure: Posterior tibial tendon passed through interosseous membrane to lateral cuneiform.
• Only 30% of original strength restored but improves function.
• Spinal surgeries (e.g., microdiscectomy) for root compression.
• Postoperative Rehab: Critical for function and gait re-training

 

Summary and Future Directions

• Foot drop is a multifaceted condition requiring precise diagnosis
• Peripheral causes (especially CPN) are most common and treatable
• Clinical evaluation + EMG/NCS + imaging is the gold standard for diagnosis
• Non-surgical care first, with AFOs and PT forming the core
• Surgery is reserved for severe, persistent, or anatomically confirmed lesions
• Early detection and interdisciplinary care yield better functional outcomes
• Continued research needed on optimal timing and technique.