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Inferior calcaneal nerve (Baxter’s nerve)

The inferior calcaneal nerve, commonly known as Baxter’s nerve, is the first branch of the lateral plantar nerve, itself a division of the tibial nerve. It provides motor innervation to the abductor digiti minimi muscle and sensory fibers to the periosteum of the calcaneus and plantar fascia.

Clinically, Baxter’s nerve is a key structure in chronic plantar heel pain, often compressed between the abductor hallucis muscle and the quadratus plantae or by the medial calcaneal tuberosity. Entrapment or irritation of this nerve leads to Baxter’s neuropathy, a condition frequently mistaken for plantar fasciitis.

Synonyms

  • First branch of the lateral plantar nerve

  • Abductor digiti minimi nerve

  • Inferior calcaneal branch of tibial nerve

Origin, Course, and Termination

  • Origin: Arises from the lateral plantar nerve near the medial calcaneal tuberosity, typically deep to the abductor hallucis muscle

  • Course: Travels anteriorly and laterally between the abductor hallucis and quadratus plantae muscles, crossing the plantar aspect of the calcaneus

  • Termination: Ends by entering and supplying the abductor digiti minimi muscle on the plantar aspect of the foot

Relations

  • Medially: Abductor hallucis muscle

  • Laterally: Quadratus plantae and abductor digiti minimi muscles

  • Superiorly: Medial calcaneal tuberosity and plantar fascia

  • Inferiorly: Plantar aponeurosis

  • Anteriorly: Joins fibrous septa between foot muscles before entering abductor digiti minimi

  • Posteriorly: Lies close to the medial process of the calcaneal tuberosity, where entrapment frequently occurs

Function

  • Motor: Innervates the abductor digiti minimi muscle, aiding abduction of the fifth toe

  • Sensory: Provides branches to the periosteum of the calcaneus and plantar fascia, contributing to heel sensation

  • Clinical role: Its entrapment is a major cause of inferomedial heel pain, often indistinguishable from plantar fasciitis on symptoms alone

Clinical Significance

  • Baxter’s neuropathy: Compression or entrapment of the inferior calcaneal nerve causing burning or aching heel pain

  • Common sites of entrapment:

    • Beneath the abductor hallucis fascia

    • Between abductor hallucis and quadratus plantae

    • Adjacent to the medial calcaneal tuberosity

  • Associated conditions: Plantar fasciitis, calcaneal spurs, tarsal tunnel syndrome

  • Symptoms: Medial heel pain radiating laterally, numbness in lateral heel, worsened by prolonged standing or walking

  • Clinical differentiation: Unlike plantar fasciitis, Baxter’s neuropathy causes neuropathic pain and sensory changes rather than pure fascial tenderness

  • Treatment: Conservative management with orthotics and physiotherapy; nerve decompression in refractory cases

MRI Appearance

  • T1-weighted images:

    • Normal nerve: low-to-intermediate signal intensity, appearing as a fine linear or oval structure coursing beneath the abductor hallucis

    • Adjacent fat planes: bright, helping delineate the nerve

    • Chronic compression: loss of surrounding fat signal, nerve thickening or flattening

  • T2-weighted images:

    • Normal nerve: intermediate signal

    • Entrapment or neuritis: increased signal intensity, thickened appearance

    • Denervated abductor digiti minimi: hyperintense T2 signal due to edema or fatty infiltration

  • STIR:

    • Normal nerve: low signal.

    • Pathology: bright hyperintense signal indicating edema or neuritis.

    • Useful for detecting muscle denervation edema before fatty replacement.

  • Proton Density Fat-Saturated (PD FS):

    • Normal: low-to-intermediate signal with sharp margins

    • Pathology: focal bright signal along nerve path or within abductor digiti minimi muscle

    • Sensitive for nerve edema, perineural fibrosis, and subtle compression changes

  • T1 Fat-Sat Post-Contrast:

    • Normal: minimal or no enhancement

    • Pathologic nerve: diffuse or nodular enhancement from inflammation or entrapment

    • Chronic denervation: fatty replacement of abductor digiti minimi visible as bright T1 signal

CT Appearance

Non-Contrast CT:

  • Nerve not directly visualized due to small caliber

  • Indirect findings:

    • Medial calcaneal spur compressing expected nerve pathway

    • Thickened plantar fascia or abductor hallucis muscle hypertrophy narrowing nerve channel

    • Bony changes at medial calcaneal tuberosity suggesting chronic entrapment

MRI images

Inferior calcaneal nerve (Baxter’s nerve) axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

Inferior calcaneal nerve (Baxter’s nerve) axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

MRI images

Inferior calcaneal nerve (Baxter’s nerve) axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00002

MRI images

Inferior calcaneal nerve (Baxter’s nerve) axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00003