Fibular Head Fracture with Common Peroneal Nerve (CPN) Palsy - Management Protocol

(10-mark MS Final Exam Answer)

Anatomy Recap (Why it Matters)

• Superficial peroneal nerve - supplies peroneus longus & brevis (eversion), and sensation over anterolateral leg and dorsum of foot
• Deep peroneal nerve - supplies tibialis anterior, EHL, EDL, EDB (dorsiflexion and toe extension), and sensation to the 1st web space

Fig. - Common, superficial, and deep peroneal nerves (Campbell's Operative Orthopaedics, 15th Ed 2026)

1. Classification of Nerve Injury (Sunderland/Seddon)

• In closed fibular head fractures: most injuries are neuropraxia or axonotmesis (neurapraxia heals automatically; axonotmesis has good prognosis)
• Neurotmesis is rare with closed fractures

2. Clinical Features of CPN Palsy

• Foot drop (loss of ankle dorsiflexion)
• Loss of toe extension
• Loss of foot eversion (peroneus longus and brevis)
• High-stepping gait

• Dorsum of foot and toes
• Anterolateral distal leg
• First web space (deep peroneal territory)

3. Investigations

• Done at 72 hours to 3 weeks post-injury
• Nerve Conduction Studies (NCS): Peroneal motor conduction velocity shows slowing and amplitude drop across the fibular head - this localizes the lesion
• EMG (needle): Fibrillation potentials, positive sharp waves in tibialis anterior, EHL, peronei indicate axonotmesis. Absent activity = complete lesion
• Prognostic value: If CMAPs (compound muscle action potentials) are preserved, prognosis is good (neuropraxia)

• X-ray knee (AP, lateral): For fibular head/neck fracture - characterize displacement, associated tibial plateau or knee injury
• MRI knee: For associated ligamentous injury, multiligamentous knee injury (which raises CPN palsy risk to 45%), intraneural ganglia
• Ultrasound of CPN: To identify compressive hematoma, neuroma, entrapment

4. Management Protocol

STEP 1: Initial Assessment and Fracture Management

• Vascular assessment (popliteal artery - ABI, doppler) - especially in knee dislocations/complex fractures
• Compartment syndrome assessment

• Isolated fibular head fractures without significant displacement and without associated ligamentous disruption: conservative management (short leg brace/cast, protected weight bearing)
• Surgical exploration of the fracture site carries risk of additional damage to the CPN and is not indicated solely for the fracture unless associated with knee dislocation / multiligamentous injury requiring operative repair (Rockwood & Green, 10th Ed 2025)

STEP 2: Immediate Conservative Management (for Neuropraxia/Mild Axonotmesis)

1. Ankle-foot orthosis (AFO) - "ankle brace": Prevents equinus deformity and foot drop complications. Applied immediately.
2. Physiotherapy:
   • Passive range-of-motion of ankle and foot (prevent contractures)
   • Active exercises for preserved muscles
   • Electrical stimulation of denervated muscles
3. Padding/protection: Knee pad over lateral knee to prevent further compression. Remove offending compressive elements (tight casts, bandages, cross-leg positioning).
4. Patient education: Avoid leg crossing, prolonged kneeling, pressure on lateral knee.
5. Observation: Most cases of neuropraxia spontaneously resolve over weeks to months (Harrison's Principles of Internal Medicine, 22nd Ed 2025)

STEP 3: Decision for Surgical Intervention

1. Open fracture with visible nerve damage
2. No clinical or electrophysiological recovery at 3-4 months
3. Suspected nerve laceration on imaging
4. Progressively worsening deficit
5. Compressive lesion (hematoma, callus, intraneural ganglion) on imaging

STEP 4: Surgical Technique - Neurolysis / Nerve Repair

• Begin incision proximal to injury (medial to biceps tendon)
• At fibular head - curve anteriorly over neck of fibula and distally along anterolateral leg
• Identify nerve on medial side of biceps tendon; trace distally as it curves around neck of fibula between peroneus longus origin and bone
• At fibular neck: nerve divides into superficial and deep branches

1. External neurolysis: Release of compressing fibrotic tissue, hematoma, callus - most common; relieves symptoms in majority of entrapment/compression cases
2. Internal neurolysis (intraneural): For intraneural fibrosis
3. End-to-end neurorrhaphy: For clean lacerations with small gap; requires tension-free repair
4. Nerve grafting: For gaps >2-3 cm; autogenous interfascicular grafting is preferred (sural nerve from contralateral leg preferred if ipsilateral sensory function is intact)
   • Flexing the knee allows closure of gaps up to 10-12 cm in the popliteal fossa
   • Postoperative immobilization: Hip spica cast x 6 weeks (not just long leg cast - suture lines tend to separate due to tension between fibula and pelvis), then gradual knee extension over next 6 weeks

• Under most favorable circumstances (low lesion, small gap, early repair): 60-70% achieve useful motor recovery (foot dorsiflexion against gravity)
• Nerve suture useful if performed before 12-15 months post-injury
• 87% of patients with partial palsy achieve full motor recovery vs. only 38% with complete lesions (Campbell's, citing systematic review)

STEP 5: Management of Persistent Foot Drop (Late/Failed Cases)

1. Tendon transfer - Posterior tibial tendon transfer (PTT transfer): Transfers tibialis posterior tendon through the interosseous membrane to the dorsum of the foot - provides active dorsiflexion; recommended after 1 year of confirmed persistent foot drop
2. Peroneal nerve grafting as a salvage procedure
3. AFO long-term if patient is not a surgical candidate
4. Ankle arthrodesis - last resort for flail ankle

5. Summary Algorithm

Fibular Head Fracture + CPN Palsy
            |
    Immediate: X-ray, vascular assessment, AFO
            |
     Open fracture?
    YES -------> Explore + repair nerve early
     NO
            |
    EMG at 3-6 weeks
            |
    Incomplete / Neuropraxia  -->  Conservative (AFO, physio, serial EMG)
            |                        |
    Complete / no recovery 3-6 mo   Resolved (most cases) --> DISCHARGE
            |
    MRI/USG - compressive lesion?
    YES --> Decompress (neurolysis)
    NO  --> Nerve exploration + repair/grafting
            |
    Foot drop > 1 year, no recovery
            |
    Posterior tibial tendon transfer

6. Key Points for Exam

• CPN is the most commonly injured peripheral nerve in lower limb trauma - Campbell's Operative Orthopaedics
• In closed fibular head fractures, the lesion is usually neuropraxia - heals spontaneously
• The fibular head fracture itself does not require fixation; exploration at this level risks further CPN damage
• EMG at 3-6 weeks is the cornerstone for prognostication
• AFO (ankle foot orthosis) is applied immediately in all patients
• Nerve repair results: 60-70% achieve useful dorsiflexion after favorable repair
• Posterior tibial tendon transfer for persistent foot drop >1 year

• Campbell's Operative Orthopaedics, 15th Ed 2026 - Sections on Common Peroneal Nerve and Knee Dislocation
• Rockwood and Green's Fractures in Adults, 10th Ed 2025
• Harrison's Principles of Internal Medicine, 22nd Ed 2025
• Localization in Clinical Neurology, 8th Ed
• S. Das - A Manual on Clinical Surgery, 13th Ed
• Chow AL et al. "Clinical Outcomes After Neurolysis for the Treatment of Peroneal Nerve Palsy: A Systematic Review and Meta-Analysis." Ann Plast Surg, 2021 [PMID: 34397520]