Foot Drop

Other Names

• Deep Peroneal Nerve Injury
• Superficial Peroneal Nerve Injury
• Common Peroneal Nerve Injury
• Peroneal Neuropathy
• Peroneal nerve compromise
• Peroneal Neuropraxia
• Foot drop
• Peroneal Nerve Palsy

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Background

• This page refers to peripheral neuropathies of, referred to as peroneal nerve injury (PNI), or more commonly 'Foot Drop'
  • Common Peroneal Nerve (CPN)
  • Deep Peroneal Nerve (DPN)
  • Superficial Peroneal Nerve (SPN)

History

• First described in 1838 (need citation)
• PNI following ankle sprain first described by Hyslop in 1941

Epidemiology

• One study found Peroneal Nerve Injuries were the most common lower extremity neuropathy in athletes
• Of 303 patients preventing with foot drop, 31% were found to be due to peroneal neuropathy
• Nerve involvement
  • Krivickas et al found the majority of cases were CPN or proximal DPN

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Introduction

Illustration of foot drop

Foot drop on the right foot. Note the relative resting position in plantarflexion comapred to the left

Common (blue) and superficial (purple) peroneal nerve branch cutaneous distributions and motor branches

Cutaneous innervation of the leg, ankle and dorsum of foot

General

• Defined as weakness or inability to dorsiflex the ankle, most commonly due to dysfunction of the neural pathway to the dorsiflexor muscles, such as L5 radiculopathy or peroneal nerve injury
• Present with a high-stepping gait and may compensate with abnormal walking patterns to avoid tripping, often accompanied by muscle weakness and sometimes sensory deficits
• Diagnosis relies on a thorough history, physical examination, and localization of the lesion using electrodiagnostic studies and imaging modalities
• Management includes addressing the underlying etiology, physical therapy, use of ankle-foot orthoses
• See also: Neuropathies Main

Etiology: Traumatic

• Knee Dislocation
  • CPN Palsy is seen in 5-40% of knee dislocations
• Proximal Fibula Fracture
• Proximal Tibia Fracture
• Tibial Plateau Fracture
  • Estimated 1% incidence (need citation)
• ACL Injury, less commonly other ligamentous injuries
• Ankle Fracture
• Ankle Sprain
  • Occurs due to traction to the peroneal nerve at the fibular head due to stretching of the peroneal muscles
  • One study found 86% of patients with grade III, 17% of grade II had EMG evidence of peroneal nerve injury, with the vast majority resolving at 3 months follow up
• Direct trauma
  • Examples include direct impact, penetrating trauma, laceration
  • Most commonly this is around the fibular head where the nerves are most superficial

Etiology: Iatrogenic

• Arthroscopic meniscal repair
• Realignment of the knee extensor mechanism
• Knee Arthrodesis
• Total Knee Replacement
• Treatment of knee flexion contracture
• Posterior Short Leg Splint or Short Leg Cast
  • Can damage the peroneal nerve by pressure over the fibular head
  • Mitigated by padding the cast or splint in the area of the fibular head
• Tight compression or bandage
• Position during anesthesia or surgery

Etiology: Other

• Mass effect
  • Ganglion Cyst or Bakers Cyst is a common mass lesion associated with PNI, specifically the CPN
  • Bakers Cyst was the most common cause of PNI by mass effect in a study by Kim et al
  • Tumors in order of decreasing frequency, included schwannoma, neurofibroma, osteochondroma, neurogenic sarcoma, focal hypertrophic neuropathy, desmoid tumor, and glomus tumor
• Knee Osteoarthritis
  • Several case reports, including one with varus laxity
• Habitual leg crossing
• Prolonged bed rest

Anatomy of the Common Peroneal Nerve and branches

• Common Peroneal Nerve (CPN)
  • One of two branches off the Sciatic Nerve (the other is the Tibial Nerve)
  • Nerve Roots: L4 through S1
  • Bifurcation occurs above popliteal fossa, CPN then travels across lateral gastroc
  • Innervation: cutaneous aspect of lateral leg below knee
  • Dives deep to fibular head, bifurcates into DPN and SPN
• Deep Peroneal Nerve (DPN)
  • Motor innervation: extensor muscles of ankle, foot
    • Tibialis Anterior
    • Extensor Digitorum Longus
    • Peroneus Tertius
    • Extensor Hallucis Longus
    • Extensor Digitorum Brevis
    • Extensor Hallucis Brevis
  • Sensory innervation: web space between the first and second toes
• Superficial Peroneal Nerve (SPN)
  • Motor innervation: ankle eversion, plantarflexion
    • Peroneus Longus
    • Peroneus Brevis
  • Sensory innervation: skin of the lateral leg, dorsum of the foot and toes, sparing the small area between the first two toes
  • 15-28% percent of patients have an accessory peroneal nerve that branches off the superficial peroneal to supply the extensor digitorum brevis

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Risk Factors

• Sports
  • American Football
• Biomechanical
  • Prolonged squatting
• Other
  • Prolonged bed rest
  • Profound weight loss
  • Bariatric surgery (need citation)
  • Sequential compression device
• Systemic Illness
  • Diabetes Mellitus
  • Motor Neuron Disease
  • Anorexia Nervsosa (due to loss of subcutaneous fat leading to nerve compression)

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Differential Diagnosis

Differential Diagnosis Leg Pain

• Fractures & Dislocations
  • Tibial Shaft Fracture
  • Fibular Fracture
  • Tibial Stress Fracture
  • Fibular Stress Fracture
  • Proximal Tibiofibular Joint Dislocation
• Muscle and Tendon Injuries
  • Calf Strain
  • Calf Tear
  • Peroneal Tendon Injuries
  • Achilles Tendonitis
  • Achilles Tendon Rupture
  • Syndesmotic Sprain
• Neurological
  • Peroneal Nerve Injury
  • Sural Nerve Injury
  • Saphenous Neuritis
  • Acute Compartment Syndrome
  • Chronic Exertional Compartment Syndrome
• Vascular
  • Popliteal Artery Entrapment Syndrome
  • Ruptured Bakers Cyst
• Other
  • Medial Tibial Stress Syndrome
• Pediatric Considerations
  • Tibial Tubercle Avulsion Fracture
  • Tibial Tuberosity Apophysitis
  • Toddlers Fracture (Tibial Shaft Fracture)

Differential Diagnosis Neuropathy

• L5 Radiculopathy
• Lumbosacral Plexopathy
• Sciatic Nerve Injury
• Peroneal Nerve Injury

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Clinical Features

Complete foot drop of the left leg due to post-traumatic intraneural ganglion cyst

Patientw as asked to dorsiflex both feet and was unable to do so on the right. Although initially thought to be a peripheral neuropathy, he was subsequently diagnosed with a stroke.

Peroneal Neurodynamic Test. Sequence of movements: plantar flexion/inversion of the ankle, foot, and toes, followed by the hip flexion keeping the knee straight (SLR position)

Classic foot dragging seen in a patient with drop foot

History

• Need to characterize nature of the presentation including acuity (chronic vs acute), any history of trauma, etc
  • Inquire about prolonged leg crossing, compressive positions, history of back pain, recent trauma
• Typically complain of lateral lower limb and dorsal foot pain
• Concurrent low back pain or posterolateral thigh pain suggests L5 radiculopathy
• Pain usually precedes sensory changes in a similar distribution
• Patient may complain of foot drop as the first manifestation of this disorder
  • Can describe difficulty walking, tripping, slapping sound of foot
• Much less commonly central causes such as brain or spinal cord lesions may have additional features

Physical Exam: Physical Exam Leg

• Hallmark finding is weakness in ankle dorsiflexion
  • Weakness of tibialis anterior, extensor hallucis longus, extensor digitorum longus
  • Weakness in toe extension, eversion of foot may be present
• Careful sensory examination can localize the lesion
  • Sensory deficity is typically present over lateral leg, dorsal foot
• PNI should have sensory and motor deficits limited to the calf, ankle and foot
• Involvement of the knee or anything proximal suggests sciatic nerve, lumbosacral radiculopathy
• Gait analysis usually reveals a high stepping gait if the patient is compensating
• Upper motor neuron signs are typically absent
  • Reflexes can be diminished if the lesion is proximal
  • Spasticity, hyperreflexia, babinski sign suggest a proximal cause

Common Peroneal Nerve

• Sensory: Lateral calf and dorsum of foot (sparing lateral and plantar foot)
• Weakness: Ankle dorsiflexion and eversion, toe extension

Deep Peroneal Nerve

• Sensory: Area between great and second toes
• Weakness: Ankle dorsiflexion, partial eversion > inversion, toe extension

Superficial Peroneal Nerve

• Sensory: Lateral calf and dorsum of foot (sparing lateral foot)
• Weakness: Ankle eversion

Special Tests

• Tinels Test: tapping around the fibular head may reproduce symptoms
• Babinski Reflex: should be normal in patients with peripheral foot drop

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Evaluation

General Approach

• Guided by clinical localization and is typically used to identify the underlying etiology
• Especially when the diagnosis is unclear or when a structural lesion is suspected

Radiographs

• Standard Radiographs Knee, Standard Radiographs Ankle
  • Typically normal in the absence of trauma
  • Evaluate for fracture, mass lesion, arthritis

MRI

• Need minimum of 3T MRI to view peroneal nerve
• Knee/ Ankle
  • Consider MRI knee in all cases since intraneural ganglia may be the most common cause
  • Look for bony lesion, neural ganglia
• Lumbar
  • Should be obtained if a lumbar or central etiology is suspected
  • Look for evidence of L5 radiculopathy

Ultrasound

• Assess fibular head
  • Can detect nerve enlargment, masses or focal entrapment
  • Dynamic evaluation can also help localize lesions in uncertain cases

EMG/NCS

• Helpful with
  • confirm diagnosis of peroneal neuropathy
  • Exclude alternative diagnoses
  • Prognosticate
• Evaluation should include
  • Motor nerve conduction studies of the peroneal nerve, tibial nerve
  • Sensory nerve conduction studies of the sural, superficial peroneal nerves
• Findings
  • If demyelination, focal slowing or conduction block
  • If axon loss, compound muscle action potential amplitudes will be decreased
• If abnormal, must examine nerves supplied by L5 nerve root but not by peroneal nerve
  • Includes Tibialis Posterior, medial gastrocnemius,
  • Expand differential of radiculopathy, lumbosacral plexopathy, sciatic neuropathy

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Classification

The Sunderland Classification of Peripheral Nerve Injuries

• Grade 1: Conduction block +/- segmental demyelination
• Grade 2: Axon discontinuity with intact endoneurium
• Grade 3: Axon and endoneurium discontinuity with intact perineurium
• Grade 4: Axon, endoneurium and perineurium discontinuity with intact epineurium
• Grade 5: Nerve discontinuity
• Grade 6: Mixed nerve injury

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Ankle Foot Orthosis

Management

Rocker Bottom Shoe

Lateral Wedge Insert

A) pre-operative foot drop on the left; B) 24 months after surgery with restored anterior tibialis muscle function.

Nonoperative

• Indications
  • Vast majority of cases
  • No clearly identified mass or lesion which could be surgically excised

Analgesia

• General
  • Neuropathic pain is challenging to treat
  • Consider the following agents which should be individualized to the patient
• Topical lidocaine
• Capsaicin
• Selective serotonin reuptake inhibitors
• Antiepileptics
• Opioids
• μ-receptor agonists
• Heat Therapy
  • If any sensory loss, be careful to avoid thermal damage
• Ice Therapy
  • If any sensory loss, be careful to avoid thermal damage
  • Case report suggested ice applied to the fibular head lead to a peroneal nerve palsy

Orthotics

• Ankle Foot Orthosis
  • Necessary if unable to dorsiflex ankle
  • Seen with proximal deep peroneal neuropathy, common peroneal nerve
• Rocker Bottom Shoe
  • Consider if weakness of the toe extensors only (distal deep peroneal neuropathy)
  • Can be used to optimize gait, reduce energy for ambulation
• Lateral wedge
  • Consider if isolated superficial peroneal nerve palsy
  • Prevent supination from weak eversion

Other Modalities

• Iontophoresis
• Physical Therapy
  • Useful in subtle peroneal nerve injuries to help with recovery
  • If complete nerve transection or axonal loss, strengthening is not helpful, PROM may
  • Maintain ROM important to avoid heel cord contracture
• Peroneal Nerve Stimulator
  • Require an intact functioning peroneal nerve
  • Not useful in patients with peripheral nerve injury.
• Wound checks
  • Patients with sensory loss should check their feet daily to prevent progression of ulcers

Operative

• Indication
  • Mass or lesion causing neuropathy
  • Refractory pain
  • Inability to ambulate with AFO due to contracture
• Technique
  • Surgical repair or graft
  • Tibialis posterior tendon transfer (to restore active dorsiflexion)
  • Neurolysis (for chronic pain)

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Rehab and Return to Play

Rehabilitation

• Strength training shows variable efficacy depending on the underlying condition
  • Progressive resistance exercises for ankle dorsiflexors, gait training, and endurance activities.
• Stretching/ ROM
  • Important to stretch daily to prevent contracture, maintain ambulatory status
  • Patient often cant tolerate bracing if contracture develops

Return to Play/ Work

• Initial phase (0-6 weeks)
  • Device fitting (AFO or FES) with 8 dose-matched physical therapy sessions focusing on gait mechanics, strength, and endurance
• Progressive rehabilitation (6-12 weeks)
  • Advancement of strengthening exercises, treadmill training with FES if available
  • Functional activities with objective monitoring of gait parameters
• Advanced functional training (12-24 weeks)
  • Sport-specific movements, agility drills, and endurance activities
  • Monitoring for fatigue-related gait deterioration
• Return to sport criteria
  • Ankle dorsiflexion to ≥15 degrees at terminal swing
  • Normalized step length asymmetry
  • Maintenance of gait speed during endurance activities
  • Adequate balance on stabilometric testing
  • Patient-reported functional satisfaction

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Prognosis and Complications

Prognosis

• Prognosis varies widely and is dependent on etiology
• Following Knee Dislocation
  • Complete palsy holds a worse prognosis than incomplete palsy
• Following Total Knee Arthroplasty
  • Park et al found 62% of patients had maximal recovery, 38% had complete recovery at 12 months
• Those requiring surgical management
  • 84% of patients who underwent end-to-end suture repair received good recovery by 24 months
  • Of those who required grafts, under 6 cm had 75% recovery of function
  • Only 15.6% achieve muscle strength ≥4/5 at final follow up
• Predictors of good outcome
  • Patients with muscle strength grade 2/5 or above are significantly more likely to achieve greater recovery
  • Patients with intervention within first 6 weeks are 6 times more likely to demonstrate greater recovery
  • Younger patients, radicular pain and early postoperative recovery are also good predictors of better outcomes

Complications

• Physical dysfunction
• Mobility impariment
• Fall risk, injury risk
  • Increased due to impaired gait mechanics
• Ankle contracture
• Equinovarus foot deformity
• Need for surgery
• Chronic disability
  • Approximately 20% of patients require long term use of ankle foot orthosis or other assist devices
• Gait abnormalities
• Patient dissatisfaction
  • This is especially true when foot drop is a complication of spinal surgery

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See Also

• Ankle Pain (Main)
• Neuropathies (Main)
• Physical Exam Ankle
• Foot And Ankle Anatomy

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