Working Diagnosis:
Inferior calcaneal and medial plantar nerve entrapment

Treatment:
Patient underwent ultrasound-guided diagnostic injection with lidocaine to confirm diagnosis and was noted to have complete resolution of pain for several hours following the diagnostic injection. She later underwent ultrasound-guided hydrodissection of the inferior calcaneal nerve and medial plantar nerve with lidocaine and D5W. Case Photo #1 Patient reported significant improvement in symptoms at her 6-week follow-up, but at three months, her pain had returned. She underwent a second hydrodissection that again resulted in 2-3 months of relief.

Outcome:
Given persistent symptoms and recurrence following hydrodissection, the patient was referred to Orthopedic Surgery and recently underwent a tarsal tunnel release.

Author's Comments:
The patient’s symptoms were consistent with inferior calcaneal nerve and medial plantar nerve entrapment given the nature of her pain, distribution, and absence of classic plantar fasciitis symptoms. Findings on diagnostic ultrasound further supported this diagnosis with edema surrounding the involved nerves. Nerve entrapment can occur secondary to compression between abductor hallucis longus and the medial head of the quadratus plantae. Inferior calcaneal nerve entrapment has been implicated in up to 20% of chronic heel pain. Management may include rest, orthotics, taping, activity modification, and diagnostic/therapeutic injections.

Editor's Comments:
Entrapment of the first branch of the lateral plantar nerve, also known as Baxter’s nerve or the inferior calcaneal nerve, is an easily missed cause for medial heel pain despite being the pain generator in up to 20% of cases. The nerve provides motor innervation to the abductor digiti minimi (ADM) and sensory innervation to the calcaneal periosteum and long plantar ligament. Diagnosis is further complicated by symptom overlap with plantar fasciitis and high rates of co-occurrence. Entrapment is thought to occur in one of two locations: proximally between the abductor hallucis and quadratus plantae or more distally as the nerve courses anterior to the medial calcaneal tuberosity, with the first compression site more common in those with excessive pronation of the foot. Diagnostic tools include ultrasound, EMG, and MRI looking for atrophy and edema within the ADM muscle belly. Treatment includes NSAIDs, changes in shoewear, ultrasound-guided injections and hydrodissection, and, more invasively, RFA or surgical release.

References:
Rodrigues RN, Lopes AA, Torres JM, Mundim MF, Silva LL, Silva BR. Compressive neuropathy of the first branch of the lateral plantar nerve: a study by magnetic resonance imaging. Radiol Bras. 2015;48(6):368-372. doi:10.1590/0100-3984.2013.0028
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4725398/

del Sol M, Olave E, Gabrielli C, Mandiola E, Prates JC. Innervation of the abductor digiti minimi muscle of the human foot: anatomical basis of the entrapment of the abductor digiti minimi nerve. Surg Radiol Anat. 2002;24(1):18-22. doi:10.1007/s00276-002-0001-1
https://pubmed.ncbi.nlm.nih.gov/12197005/

Cozzarelli J, Sollitto RJ, Thapar J, Caponigro J. A 12-Year Long-Term Retrospective Analysis of the Use of Radiofrequency Nerve Ablation for the Treatment of Neurogenic Heel Pain. Foot & Ankle Specialist. 2010;3(6):338-346. doi:10.1177/1938640010379048
https://journals.sagepub.com/doi/10.1177/1938640010379048

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