PNS: Common Fibular Nerve Anatomy

• The common fibular nerve originates from the L4-S2 nerve roots.
• Fibers travel within the sciatic nerve until reaching the popliteal fossa.
• Distal to the popliteal fossa, it divides into superficial and deep fibular nerves.

Palpation

• Proximal to the popliteal fossa, the common fibular nerve runs along the posterolateral aspect of the leg, deep to the long head of the biceps femoris.
• It passes through the popliteal fossa before running behind the proximal fibular head.
• The nerve is covered only by skin and subcutaneous fat/fascia as it runs over the neck of the fibula, making it susceptible to injury.
• Inferior and lateral to the fibular head, the nerve divides into superficial and deep fibular nerves.
• The superficial fibular nerve runs anterolaterally between the fibularis longus and extensor digitorum longus muscles, within the lateral compartment.
• The deep fibular nerve runs anteriorly and adjacent to the anterior tibial artery, between the extensor digitorum longus and tibialis anterior muscles.
• As the deep fibular nerve travels distally, it runs in the leg's anterior compartment, between the extensor hallucis longus muscle and the tibialis anterior muscle.
• Approaching the foot anterior to the talus, the nerve divides into medial and lateral branches.
• The medial branch runs alongside the dorsalis pedis artery, terminating between the first two metatarsals.
• The lateral branch runs alongside the lateral tarsal artery and terminates near the fifth metatarsal.
• Palpate for tone and tissue health through the anterior and lateral compartments of the leg.

Function

• The superficial fibular nerve controls motor function of the fibularis longus and fibularis brevis.
• The deep fibular nerve controls motor function of the tibialis anterior, extensor digitorum longus, extensor hallucis longus, fibularis tertius, extensor hallucis brevis, and extensor digitorum brevis.
• The common fibular nerve is responsible for dorsiflexion and eversion.
• The tibial nerve is responsible for plantar flexion and inversion.
• The common fibular nerve provides sensory function for most of the dorsal surface of the foot, most of the anterolateral leg (skin over tibialis anterior), and the web space between pedal digits 1 & 2.

Pathophysiology

• The common fibular nerve is frequently injured and subject to degeneration injury (axonotmesis or neurotmesis) due to its superficial location over the fibula's neck.
• Classic presentation of injury includes loss of dorsiflexion, loss of eversion, and loss of sensation down the lateral leg and dorsum of the foot.
• Patients may present with "foot drop" because of the inability to dorsiflex the foot.
• The condition often occurs during the pre-swing and initial swing phase of the gait cycle, with toes dragging due to the loss of dorsiflexion.
• Patients may compensate by exaggerating hip abduction to allow for foot clearance.
• Mechanisms of injury: trauma/injury to the knee, fibula fracture, tight plaster cast use, regularly wearing high boots, pressure to the knee (during sleep or coma), more common in those who are very thin, have diabetes, or Charcot-Marie-Tooth disease.
• Assessment for degeneration injury includes ROM (weakness in dorsiflexion and eversion), length tests (antagonists will be shortened), and observation (foot drop, gait).
• Neurodynamic testing is not used in the context of degeneration injury.

Precautions

• Avoid tractioning the regenerating nerve and stretching denervated tissue.
• Place the leg in a neutral position with pillows.
• Apply segmental treatment proximal to the lesion using techniques perpendicular to the nerve.
• Block or stabilize tissue just proximal to the lesion to prevent drag.
• Treat flaccid tissue with light stroking and compression.
• Treat unaffected tissue distal to the lesion site with strain toward (but not onto) the flaccid tissue.
• Perform PROM to joints in the direction that shortens the affected tissue and nerve.

Goals & Approach

• Promote relaxation, decrease edema, decrease tone and TrP in muscles proximal to the lesion, and promote tissue health in denervated tissue.
• Techniques include light stroking that shortens the nerve or bunches up tissue (or is cross-fibre), gentle compressions, and segmental work (distal to lesion is okay on unaffected muscles/antagonists only).
• Prevent contracture of unopposed antagonist muscles.
• Promote joint health with PROM, if possible, and handle the limb carefully to avoid tractioning the nerve.
• Encourage returning motor function.
• Facilitatory ROODS techniques or similar, or AAROM on the returned function (incorporate visualisation) are used once some function has been regained.
• Promote tissue health using gentle Swedish techniques or sensory stimulation with different textures.

Hydrotherapy

• Contraindicated if autonomic dysfunction is present; avoid anywhere on the affected limb, even proximal to the lesion site.
• If autonomics are not affected: cool compress over acute injury, modified temperature used over affected tissue, and mild contrast washes can be used.

Home Care

• Vigilance for pressure sores if wearing a splint.
• Perform PROM of joints that shortens affected tissue.
• Visualize performing actions with the affected limb.
• Elevate the limb if edema is present.

Assessment

• Straight Leg Raise (Common Fibular Nerve Bias): internally rotate the thigh, extend the knee, invert the foot, flex the hip, and plantar flex the ankle with cervical flexion for the sensitizing test. A positive test recreates symptoms in superficial or deep fibular distributions.
• MMT or RROM is used to test tibialis anterior, extensor digitorum longus, extensor hallucis longus, fibularis tertius, extensor hallucis brevis, extensor digitorum brevis, fibularis longus, and fibularis brevis.
• Sensory testing is performed on the anterolateral lower leg and dorsum of the foot.