Lateral Plantar Nerve Entrapment

Lateral plantar nerve entrapment also known as lateral plantar neuropathy is a cause of lateral foot pain with weightbearing.
==Anatomy==
The sciatic nerve runs down the leg and divides into the common peroneal nerve and tibial nerve near the popliteal fossa. At the ankle the tibial nerve is often called the posterior tibial nerve even though it is not a separate branch.
The posterior tibial nerve courses down the foot through the tarsal tunnel and ramifies into the lateral plantar nerve, medial plantar nerve, and the medial calcaneal nerve. There are independent medial and lateral plantar tunnels separated by the medial septum between the medial calcaneus and the deep fascia of the abductor hallucis.
The lateral plantar nerve has several divisions including the clinically relevant Baxter's nerve or the inferior calcaneal nerve.
==Aetiology==
*Trauma/surgery: ankle sprain, soft tissue trauma, failed tarsal tunnel release, harvest of flexor hallucis longus tendon (but medial plantar nerve injury is more likely)
*Lesions: Neurilemmoma, pseudoganglion.
*Foot abnormalities: increased foot pronation, midtarsal joint laxity, forefoot varus, rear foot eversion, pes planus, cavovarus foot, hypertrophy of abductor hallucis from running.
==Epidemiology==
It is less common than entrapment of its first branch, Baxter's nerve (inferior calcaneal nerve).
==Clinical Features==
LPN entrapment can occur along with entrapment of other local nerves and so the clinical picture can be tricky.
===History===
Patients have burning pain, paraesthesias, and numbness involving the lateral side of the sole and lateral toes. Symptoms are typically worse with weight-bearing activities and improve with rest. However symptoms can occur at rest.
===Examination===
There may be tenderness and paraesthesias when the abductor hallucis is palpated. 
There may be reduced pinprick sensation over the lateral aspect of the foot corresponding to the sensory territory of the lateral plantar nerve. Motor deficit is rare.
Tinel's sign: may be positive at the proximal and distal tarsal tunnel. 
Plantar Flexion-Inversion Test: The foot is plantar flexed and inverted with pressure applied under the abductor hallucis.
Dorsiflexion-Eversion Test: Pressure over the proximal tarsal tunnel. This compresses the lateral plantar nerve, inferior calcaneal nerve, and medial plantar nerve.
==Differential Diagnosis==
==Investigations==
Obtain weight-bearing plain films to assess foot alignment and exclude fractures and osteoarthritis.
MRI may identify denervation changes, masses, and tendon abnormalities.
Nerve conduction studies of the lateral plantar nerve may be abnormal.
==Treatment==
Identify and manage any factors contributing to increased foot pronation: obesity, midtarsal joint laxity, forefoot varus, rear foot eversion, pes planus, cavovarus foot, etc. Orthotics may be helpful. Stretching the plantar fascia and Achilles tendon may reduce stress on the soft tissues. Weight loss and physical therapy to strengthen the intrinsic muscles to reduce hyperpronation.
Injection of the lateral plantar nerve can be diagnostic and therapeutic.
==References==
Category:Foot and Ankle Conditions
Category:Mononeuropathies