Keys To Detecting And Treating Entrapment Neuropathies

Jodi Schoenhaus, DPM, and Jason Gold, DPM

   Entrapment neuropathy of the tarsal tunnel and its terminal branches is a painful condition, which can be challenging to diagnose given the possibility of concurrent conditions with overlapping symptoms. Heel spur syndrome/plantar fasciitis and entrapment neuropathy often present at the same time. However, it is important to differentiate clearly between the two pathologies as entrapment neuropathy has a distinct history and clinical presentation.

   The anatomic outline of the posterior tibial nerve and its branches is pertinent to the appropriate diagnosis and management of the entrapment neuropathy. Following the course of the posterior tibial nerve will lead you to the site of entrapment. The posterior tibial nerve courses posterior to the medial malleolus in a fibroosseous compartment and just deep to the flexor retinaculum, which is one potential site of entrapment. At the distal end of the tarsal tunnel, the tibial nerve branches into the larger medial plantar nerve and smaller lateral plantar nerve. At the level of bifurcation, a fascial septa separates the nerves, leading them into their respective courses that innervate the plantar foot.

   This fibrous band is another potential site of nerve entrapment. The medial plantar nerve courses superficial to the abductor hallucis muscle and sends motor and sensory branches to the plantar medial aspect of the foot. The lateral plantar nerve travels through a fibrous opening of the abductor hallucis.

   The first branch of the lateral plantar nerve, Baxter’s nerve, arises at this location. It transverses laterally and passes anterior to the medial calcaneal tuberosity (often the site of a heel spur) to innervate the abductor digiti quinti muscle.1,2 The Baxter’s nerve is often entrapped at the abductor hallucis muscle and one must release this nerve surgically.

What To Look For In The Clinical Exam

   Often mistaken for plantar fasciitis with heel spur syndrome, entrapment neuropathy of Baxter’s nerve is a painful condition that can lead to chronic heel pain. Typically, a patient will present with pain on the plantar medial aspect of the heel that exponentially increases in severity the longer the individual is weightbearing.

   The discomfort begins as an ache, progresses to a burning pain and eventually leads to numbness. These sensations can travel proximal toward the medial ankle along the tarsal tunnel, the Valleix sign or across the plantar aspect of the foot laterally toward the base of the fifth metatarsal. Often the patient complains of pain shooting laterally on the plantar aspect of the heel. Unless Baxter’s nerve is entrapped and occurs in conjunction with plantar fasciitis, the pain does not present as post-static dyskinesia.

   When it comes to diagnosing entrapment neuropathy of Baxter’s nerve, the physician should ensure that the clinical examination incorporates complete and systematic rearfoot examination. The patient will point directly to the site of pain at the proximal level of the abductor hallucis muscle. This position is approximately 5 cm anterior to the posterior border of the heel at the intersection of the plantar and medial skin.3 One will elicit pain with palpation at the exact location, which is usually not the medial calcaneal tubercle nor the ligamentous band of the plantar fascia.

   The rearfoot examination includes evaluation of the Achilles tendon course and insertion. One should also check for posterior and inferior calcaneal pathology, medial and lateral compression (calcaneal squeeze test), tarsal tunnel entrapment, medial calcaneal nerve symptoms and plantar fascial pain. Physicians should also perform a gait analysis to check for for pronatory or supinatory forces causing compression on the abductor hallucis muscle.

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