Baxter's Nerve Entrapment

Original Editor - [User:|,Habibu Salisu Badamasi]
Top Contributors - Habibu Salisu Badamasi and David Olukayode

Introduction

The most common complaint in the foot and ankle region is heel pain. The most of these problems, however, are related to plantar fasciitis. Up to 20% of cases of chronic heel pain are caused by Baxter's nerve entrapment. However, it's an often-overlooked source of heel pain.

Clinically Relevant Anatomy

Baxter’s nerve also known as inferior calcaneal nerve, is the first branch of the lateral plantar nerve arising within the tarsal tunnel. lateral plantar nerve has sensory components to the calcaneal periosteum, the long plantar ligament and the lateral plantar skin, and motor fibers to the abductor digiti minimi, flexor digitorum brevis and quadratus plantae. The first branch of the lateral plantar nerve originates from the lateral plantar nerve near the bifurcation of the tibial nerve or it may arise from the tibial nerve prior to its bifurcation. It then dives through the superficial fascia at the superior border of the abductor. At this level, the investing fascia of the abductor is thicker laterally because of the reinforcement from the interfascicular ligament in continuity with the medial intermuscular septum. It travels distally between the lateral abductor fascia and the medial edge of the quadratus. When it reaches the lower border of the abductor hallucis, it turns and courses laterally, passing 5.5 mm anterior to the medial calcaneal tuberosity (or spur) and between the quadratus and the underlying flexor brevis until it reaches its distal target of the abductor digiti minimi.

Etiology

Baxter's nerve is vulnerable to entrapment because of its course, and the most common location is the tight fascia of the abductor hallucis and the medial aspect of the quadrates plantae muscle. However, two point have been proposed as possible entrapment reasons.

1. The first is the point where the nerve turns laterally between the medial edge of the quadratus plantae and the thick lateral fascia of the abductor hallucis.
2. The second is the point where the nerve courses anterior to the tuberosity and/or spur. An increase in cubic contact of this passage (via a spur or muscle hypertrophy) and/or pronation of the rearfoot/midfoot complex, causing impingement at the nerve’s sharp turn are both possible predisposing conditions.

Clinical Presentation

• Tenderness above the abductor hallucis origin, which can induce laterally radiating discomfort and/or paraesthesia.
• A sharp, radiating pain worse at night and after physical activity (such as walking).
• Moderate atrophy of the abductor digiti minimi muscle.
• Pain across the medial calcaneus.

Examination

Biomechanical exam

Typically, therapists will notice a pronated foot structure during the biomechanical assessment.

Special tests

• Tinel's test.
• Phalen’s test (passive inversion and plantar flexion of the foot).
• Windlass test to rule out Plantar Fasciitis.

Radiography and Bone scan

Osseous pathology can be ruled out with simple radiographs and bone scans.

Serologic testing

Serologic testing may be used to rule out systemic arthropathy.

Differential diagnosis

• Plantar fasciitis
• Seronegative arthritis-induced inflammation
• Tarsal tunnel syndrome
• Medial calcaneal neuritis
• Heel spurs
• Trauma
• Fat pad atrophy
• Calcaneal stress fractures
• Periosteal inflammation

Treatment and Management

Medical treatment

NSAIDs and anticonvulsants can aid in symptom relief.

Conservative treatments

• Kinesio taping or orthotics use at the foot.
• Stretching and strengthening exercises at the foot.
• Cryoablation, radiofrequency, hydrodissection using 5% dextrose, or ultrasound-guided corticosteroid injection.

Surgery

Surgical release/decompression of the nerve.