Common Peroneal Nerve

Anatomy

  • L4 to S2, the lateral division of the sciatic nerve
  • Winds around the fibular neck through the fibular tunnel under peroneus longus
  • Superficial peroneal nerve supplies the peronei and most of the dorsum of the foot
  • Deep peroneal nerve supplies tibialis anterior, EHL, EDL, peroneus tertius, EDB and the first web space
  • Vulnerable as superficial, tethered, with few large fascicles and a long course

Aetiology

  • Knee dislocation, especially with posterolateral corner injury, varus traction stretching a long zone
  • Biceps femoris avulsion and fibular head avulsion fractures
  • Fibular neck and tibial plateau fractures
  • Pressure from casts, bandages, theatre positioning, leg crossing, bed rest and rapid weight loss
  • Iatrogenic in HTO, fixed valgus correction in knee arthroplasty, inside-out lateral meniscal repair and fixator pins

Clinical Features

  • Foot drop with high stepping gait, weak dorsiflexion and eversion, dorsal foot sensory loss
  • Inversion (tibialis posterior) and plantarflexion preserved
  • L5 radiculopathy also weakens tibialis posterior and gluteus medius

Investigations

Common Peroneal Nerve, tibial and common peroneal (fibular) nerves
Tibial and common peroneal (fibular) nerves. Image by Anatomist90, Wikimedia Commons, CC BY-SA 3.0.
  • NCS and EMG at 3 to 4 weeks, including short head of biceps to exclude a sciatic lesion
  • MRI or ultrasound for ganglion, tumour or discontinuity

Management

  • Remove external pressure, after knee arthroplasty loosen dressings and flex the knee
  • AFO and daily calf stretching prevent equinus while awaiting recovery
  • Open injuries explored, sharp lacerations repaired primarily
  • Closed traction injuries observed, explored if no clinical or electrical recovery by about 3 months
  • Neurolysis, grafting (poor with long grafts) or tibial branch transfer to the deep peroneal motor branch
  • Intraneural ganglia decompressed with articular branch ligation to prevent recurrence

Tibialis posterior transfer

  • Standard transfer for persistent foot drop, through the interosseous membrane to the lateral cuneiform
  • Bridle procedure splits it to tibialis anterior and peroneal tendons
  • Needs an intact tibial nerve, adequate tibialis posterior power and a supple ankle
  • Most walk without an orthosis, with limited active dorsiflexion

Prognosis

  • Poorer recovery than the tibial nerve
  • Complete lesions after knee dislocation with a long zone often do not

Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.