Lateral Plantar Nerve Entrapment (Baxter's Neuropathy): Comprehensive Guide to Diagnosis & Surgical Anatomy
Key Takeaway
Baxter's neuropathy, or lateral plantar nerve entrapment (LPNE), is a common yet often overlooked cause of chronic heel pain, affecting 10-20% of patients with refractory symptoms. It involves compression of the first branch of the lateral plantar nerve (FBLPN), often between foot muscles or bone, requiring precise diagnosis and understanding of its surgical anatomy for effective treatment.
A 45-year-old long-distance runner presents with a 14-month history of chronic, recalcitrant medial plantar heel pain. They have failed extensive non-operative management, including orthotics, physiotherapy, and multiple corticosteroid injections. They describe a burning, radiating pain that is worst during the push-off phase of gait. On examination, there is maximal tenderness over the medial calcaneal tuberosity and a positive Tinel’s sign at the medial heel. What is your primary differential diagnosis, and how would you investigate this to confirm your suspicion?
Candidate: I suspect Baxter’s neuropathy (entrapment of the first branch of the lateral plantar nerve). I would perform an MRI to look for atrophy or fatty infiltration of the abductor digiti minimi muscle and evidence of nerve edema. I would also consider an ultrasound-guided diagnostic lidocaine block to see if it provides temporary relief, which would confirm the diagnosis.
Candidates often focus solely on the MRI and neglect the diagnostic nerve block. They also fail to mention excluding other pathologies (e.g., stress fracture, tarsal tunnel syndrome) or fail to acknowledge the high false-negative rate of EMG/NCS, leaving the examiner wondering if they understand the diagnostic limitations of the condition.
Start by identifying the primary diagnosis: Baxter’s neuropathy. Systematically outline the investigative path: 1. Clinical confirmation: Palpation of the FBLPN course and Tinel’s test. 2. Advanced Imaging: MRI to identify ADM atrophy/edema or associated bony impingement. 3. Diagnostic Injection: Ultrasound-guided lidocaine block at the point of maximal entrapment (most critical). 4. Differential Exclusion: Mention ruling out plantar fasciitis (distinct anatomical location), tarsal tunnel syndrome, and lumbar radiculopathy. Finally, note that EMG/NCS may be considered but has low sensitivity for this specific branch.
The patient has been scheduled for surgical decompression. Describe the key anatomical structures you must encounter and protect during this procedure, and how you would systematically perform the decompression.
Candidate: I would approach the nerve via a medial curvilinear incision. I must identify and protect the medial calcaneal nerve branches. The main steps are to incise the fascia of the abductor hallucis, retract the muscle, locate the FBLPN arising from the lateral plantar nerve, and release the fibrous bands at the deep fascial origin from the calcaneal tuberosity. I would also check for compression between the quadratus plantae and the calcaneus.
Candidates often fail to mention the medial calcaneal nerves, which are easily injured, leading to a painful sensory deficit. They also fail to mention the use of loupe magnification, which is essential for safely identifying a nerve that can look like fibrous connective tissue.
Structure the answer by surgical layers: 1. Superficial: Protection of sensory medial calcaneal nerve branches. 2. Deep: Incision of the Abductor Hallucis deep fascia. 3. Dissection: Use loupe magnification to identify the FBLPN as it turns around the medial calcaneal tuberosity. 4. Decompression: Longitudinal release of the fibrous band between the deep fascia of the abductor hallucis and the origin of the quadratus plantae. 5. Verification: Passing a blunt probe to ensure complete release of all identified constriction sites, ensuring no compromise to the medial plantar artery.
