Common Peroneal Nerve

1. Introduction

2. History

• The peroneal nerve and foot drop have been recognised since antiquity, with the term "peroneal" derived from the Greek perone (fibula).
• Sir Herbert Seddon (1942) and Sir Sydney Sunderland (1951) developed the nerve injury classification systems still used today.
• The condition was historically recognised in occupational settings (strawberry pickers, textile workers) and in soldiers after prolonged crouching (trench palsy).
• "Punter's palsy" - peroneal injury from ankle inversion while kicking - was described in American football literature.
• The concept of intraneural ganglia from the superior tibiofibular joint as an underappreciated cause was clarified in modern imaging studies.

3. Anatomy

Origin and Root Value

• Root values: L4, L5, S1, S2
• Arises as the lateral division of the sciatic nerve, separating from it in the posterolateral aspect of the popliteal fossa (or higher in the thigh in cases of early bifurcation)

Course

Branches

1. Superficial peroneal nerve - innervates peroneus longus and brevis (ankle eversion); sensory to anterolateral distal leg and dorsum of foot (except 1st web space)
2. Deep peroneal nerve - innervates tibialis anterior, extensor digitorum longus, extensor hallucis longus, extensor digitorum brevis (ankle dorsiflexion, toe extension); sensory to 1st dorsal web space
3. Recurrent articular nerve - sensory to knee joint
4. Lateral sural cutaneous nerve - sensory to upper lateral leg

Motor Innervation Summary

Anatomical Diagram

MRI Anatomy - Axial View at Knee (Distal Popliteal Fossa)

Why Is the CPN So Vulnerable?

1. Superficial course around the fibular neck - no deep muscle coverage
2. Tethered proximally by the biceps femoris tendon and distally by the peroneus longus arch
3. Limited excursion - the nerve has restricted ability to move away from the fibular head
4. Bony prominence - the fibular head acts as a pulley, concentrating mechanical stress
5. Early proximal bifurcation in some individuals increases the exposure length
6. Fascicular arrangement - the deep peroneal fascicles lie on the deep surface at the fibular neck, pressed directly against bone

4. Etiology

Traumatic

Compressive / Positional

Space-Occupying Lesions

• Baker cyst extending into retropopliteal space
• Intraneural ganglion (from superior tibiofibular joint - an underrecognised but treatable cause)
• Ganglion cyst, lipoma, osteochondroma at fibular head
• Hematoma, aneurysm

Medical/Systemic

• Diabetic neuropathy - lower ischaemic threshold predisposes to entrapment
• Vasculitis - nerve infarct
• Leprosy
• Anorexia nervosa / cancer / AIDS - emaciation removes protective fat padding

Iatrogenic

• Postoperative positioning (lateral decubitus, lithotomy)
• Orthopaedic operations (high tibial osteotomy, TKA)
• Poorly applied casts, bandages, or splints

5. Mechanism

General Mechanisms

6. Pathology

Wallerian Degeneration

Nerve Regeneration Rate

• Axonal regeneration proceeds at 1-3 mm/day (approximately 1 inch per month)
• Grade 1-2 injuries: rapid regeneration, excellent recovery
• Grade 3: slower (~1 mm/day), incomplete and unpredictable
• Grades 4-5: no spontaneous regeneration; requires surgical intervention

Denervation Changes in Muscle

• Fibrillation potentials appear on EMG within 3 weeks of axonal injury
• Muscle atrophy begins within weeks; irreversible after approximately 12-18 months
• This establishes the critical window for surgical nerve repair (should not exceed 12 months)

7. Clinical Features

Symptoms

• Foot drop - inability to dorsiflex the foot; the hallmark presentation
• High-stepping gait (steppage gait) - hip and knee flexed excessively to clear the toe from the ground
• Sensory loss over anterolateral leg and dorsum of foot (deep peroneal pattern: 1st web space only; superficial peroneal: broader dorsum)
• Pain - variable; more common with intraneural ganglia or entrapment
• Onset may be acute (trauma) or noticed on waking (compression during sleep)

Signs

Selective Deep Peroneal Involvement

Differential Diagnosis of Foot Drop

8. Investigation

Clinical

• Detailed neurological examination (motor testing, sensory mapping, reflexes)
• Tinel's sign at fibular head
• Assessment for systemic causes (diabetes, weight loss, vasculitis)

Electrodiagnostic Studies (Gold Standard)

Laboratory

• Blood glucose / HbA1c (diabetes screen)
• ESR, ANCA, cryoglobulins (if vasculitis suspected)

9. Radiograph

• Fibular head/neck fractures - up to 50% have associated CPN injury
• Knee dislocation - identifies bony injury
• Tibial plateau fractures - associated with posterolateral corner and CPN injury
• Calcification near fibular head suggesting ganglion calcification or bony lesion
• Assessment of alignment (valgus knee increases CPN stretch risk)

10. CT

• Characterising bony lesions (osteochondroma, exostosis) compressing the nerve
• Fracture detail at fibular head - exact fracture pattern, displacement
• Pre-operative planning for complex periarticular fractures
• Identifying calcified ganglia
• CT myelogram if MR contraindicated and radiculopathy is in the differential

11. MRI

Normal MRI Appearance

• Nerve appears as small bundles of fascicles in a supporting fatty background
• Isointense to muscle on T1; slightly hyperintense on T2/PD
• Best seen on axial sequences; nerve typically visible in most routine knee MRI sequences

Pathological Findings

MRI Knee Series (Axial)

MRI Protocol

• Knee MRI: Standard sequences + dedicated axial T1 spin echo for nerve mapping
• High-resolution peripheral nerve MRI (MR neurography): 3T, 3D STIR or DWIBS sequences; allows nerve tracking from sciatic origin to distal branches
• Coverage should extend from proximal thigh to proximal fibula to encompass entire vulnerable segment

12. Classification

Seddon Classification (1942)

Sunderland Classification (1951) - More Detailed

Classification by Location

13. Treatment

Management Flowchart

A. Non-Operative Management

• Neurapraxia (Sunderland grade 1) / low-energy compressive injuries
• Axonotmesis with reasonable recovery potential
• Systemic/metabolic cause amenable to treatment

• Avoid leg crossing, prolonged squatting
• Rapid weight loss if entrapment related to obesity causing excess pressure
• Treat underlying diabetes, vasculitis, hypothyroidism
• Pad lateral knee if continued pressure unavoidable

• Rigid or articulated AFO maintains ankle in neutral dorsiflexion during swing phase
• Provides:
  • Toe dorsiflexion during swing phase
  • Medial/lateral stability at ankle during stance
  • Push-off stimulation during late stance
• Carbon fibre AFOs are lightweight and functionally superior to traditional polypropylene

• Maintain joint range of motion to prevent contracture
• Stretching of triceps surae to prevent equinus
• Strengthening of intact muscle groups
• Gait retraining

• Peroneal nerve stimulator devices (e.g., WalkAide, Bioness L300)
• Surface electrode over CPN triggers dorsiflexion during swing phase
• Increasingly used as first-line adjunct to AFO

• Neurapraxia: expect recovery within 4-12 weeks
• Axonotmesis: observe for 3-6 months for signs of reinnervation
• Serial EMG/NCS to track recovery
• No spontaneous improvement after 3-6 months → surgical re-evaluation

B. Operative Management

• High-energy injuries (laceration, fracture-dislocation, gunshot) → explore within 3 weeks
• No recovery after 3-6 months of observation (low energy) or no recovery at 3 months (axonal loss on NCS)
• Known anatomical compressor (ganglion, tumour, bony fragment)
• Intraneural ganglion confirmed on MRI

• Release of fibrous/scar tissue compressing the nerve externally (external neurolysis) or between fascicles (internal neurolysis)
• Indications: entrapment, neuroma-in-continuity (Sunderland grade 3-4), intraneural ganglion
• For intraneural ganglia: decompression + resection of articular branch + tibiofibular joint capsule repair to prevent recurrence
• Success in up to 60-70% if performed within 6 months of injury

• Primary repair: Direct epineural or fascicular suture; only if tension-free
• Indications: sharp laceration, early exploration, small gap
• Best results when performed early with short gap and low lesion
• Under ideal conditions (early, low lesion, small gap): 60-70% achieve useful dorsiflexion (anti-gravity)

• For gaps > 2-3 cm preventing tension-free repair
• Autograft (sural nerve, medial cutaneous nerve of forearm) remains the gold standard
• Mean graft length in published series: 7 cm; shorter grafts give significantly better outcomes
• Among 465 patients undergoing peroneal nerve reconstruction: 49% achieved >M3 recovery - Sabiston Textbook of Surgery
• Allograft (processed decellularised nerve) used for gaps 5-70 mm when donor site morbidity must be minimised

• Transfers a fascicle from the tibial nerve to the distal CPN (end-to-end fashion)
• Used when proximal stump unavailable or gap too long for grafting
• Meta-analysis: 62.9% achieved >M3 function with tibial-to-CPN nerve transfer
• Avoids long regeneration distances; particularly useful for proximal injuries

• For late presentations (>12-18 months), irreversible denervation, or failed nerve repair
• Standard transfer: Tibialis posterior transfer to dorsum of foot (Bridle procedure or direct transfer through interosseous membrane)
• Restores active dorsiflexion using a tibial nerve-innervated muscle
• Additional: peroneus longus to brevis transfer, toe extensor augmentation
• Most reliable and durable long-term solution for established foot drop

• Patient supine or lateral decubitus; thigh tourniquet
• Longitudinal incision from popliteal fossa, curving anterolaterally around fibular head
• Knee flexion relaxes the nerve
• Expose nerve from popliteal fossa to fibular tunnel
• Protect sural nerve branch

14. Recent Advances

1. MR Neurography (High-Resolution Nerve Imaging)

• 3T MRI with dedicated surface coils, 3D-STIR and diffusion tensor imaging (DTI) allows direct visualisation of the nerve, fascicular detail, and continuity - aiding surgical planning

2. Nerve Transfers

• Expanding use of selective tibial nerve branch transfer to deep peroneal nerve targets (tibialis anterior, EHL)
• End-to-side neurorrhaphy techniques allow partial reinnervation without fully sacrificing donor nerve

3. Intraoperative Nerve Monitoring and Nerve Stimulation

• Intraoperative EMG and nerve action potential (NAP) recording during surgery guides extent of resection vs neurolysis in neuroma-in-continuity cases

4. Nerve Conduits and Processed Allografts

• Polyglycolic acid and collagen conduits for short gaps (< 3 cm); processed nerve allografts (Avance) for 5-70 mm gaps avoiding donor site morbidity from sural nerve harvest

5. Functional Electrical Stimulation (FES) / Neuroprosthetics

• Implantable FES systems (e.g., ActiGait, Bioness L300 Plus) with closed-loop gait-triggered stimulation are now in clinical use, providing functional improvement equivalent to or better than fixed AFO

6. Platelet-Rich Plasma (PRP) and Growth Factors

• Emerging evidence for PRP injection at lesion site to promote remyelination and axonal regeneration; mostly experimental

7. Ultrasound-Guided Diagnosis and Intervention

• High-frequency ultrasound (15-18 MHz) allows real-time dynamic assessment of the nerve at the fibular head, identification of ganglion cysts, and ultrasound-guided aspiration of intraneural ganglia

8. Intraneural Ganglion - Tibiofibular Joint Repair

• Recognition that recurrence after simple decompression is reduced by articular branch excision and tibiofibular joint capsule repair - now the standard surgical approach

Quick Reference Summary

• Adams & Victor's Principles of Neurology 12th Ed - Common Peroneal Nerve, p. 1165
• Localization in Clinical Neurology 8th Ed - Lesions of the Common Peroneal Nerve, p. 154-156
• Harrison's Principles of Internal Medicine 22nd Ed - Peroneal Neuropathy
• Imaging Anatomy Vol. 3 - Peroneal Nerve, p. 307-310
• Campbell's Operative Orthopaedics 15th Ed 2026 - Peroneal Nerve Repair, p. 3017-3019
• Sabiston Textbook of Surgery 8th Ed - Outcomes After Peroneal Nerve Repair
• EFORT Open Reviews - Evidence-based algorithm for CPN injury management (2016)