Baxter's Nerve Entrapment

Baxter's nerve entrapment, also known as Baxter neuropathy, and inferior calcaneal nerve entrapment, is plantar heel pain arising from compression of the inferior calcaneal nerve (Baxter nerve). 
==Anatomy==
The inferior calcaneal nerve (Baxter nerve) is the first branch of the lateral plantar nerve, which is itself a branch of the tibial nerve. The nerve lies in between the abductor hallucis muscle and quadratus plantae.
The Gray's anatomy image and many other anatomy textbook images are incorrect. The Baxter nerve is quite posterior and lies very close to the calcaneus. It was named after Donald Baxter.
==Pathophysiology==
There are three entrapment points:
#Where the nerve runs between the deep fascia of the abductor hallucis and medial plantar margin of the quadratus plantae
#More distally along the anterior aspect of the medial calcaneal tuberosity. A calcaneal plantar enthesophyte and/or soft tissue changes of plantar fasciitis may contribute to entrapment at this second location.
==Aetiology==
The following are some causes of entrapmentA.M. Trescot (ed.), Peripheral Nerve Entrapments: Clinical Diagnosis and Management, DOI 10.1007/978-3-319-27482-9_76
*Repetitive microtrauma. E.g. those with jobs requiring prolonged standing or walking, or avid runners. Plantar fasciitis. Fat pad atrophy.
*Acute trauma. direct trauma from a fall or stepping on a hard object, scar tissue after plantar fasciotomy.
*Impingement from bony exostosis, calcaneal spur, neuroma, neurilemmoma
*Stretch injury from a hypermobile pronating foot, abductor hallucis hypertrophy in runners
*Diabetic peripheral neuropathy.
==Epidemiology==
It is estimated that up to 20% of patients with chronic heel pain may be due to Baxter nerve entrapment.
==Risk Factors==
Obesity, age, diabetes, muscle hypertrophy, hyperpronated foot, pes planus, plantar calcaneal spur, plantar fasciitis, spondyloarthritis. 
==Clinical Features==
===History===
The clinical features may be similar to or coexist with plantar fasciitis. However there may be less morning pain, occasional altered sensation, and intrinsic muscle atrophy. The pain is felt in the medial heel and is often burning. It may worsen with prolonged standing and walking. It typically has a gradual onset.
There are two groups of patients with this condition: keen runners and those involved in everyday living.
===Examination===
On examination the patient may walk with exaggerated supination to avoid placing weight on the medial heel. They are tender over the medial calcaneal tubercle similar to the location for plantar fasciitis. 
Palpate the distal Achilles tendon and retrocalcaneal bursa looking for tenderness. Also squeeze the heel to detect a stress fracture.
Look at active motion of toe abduction and adduction and compare to the other side. Assess strength with resisted abduction and adduction.
Evaluate Tinel's sign by percussing the upper and lower tarsal tunnels, however this is often absent.
==Differential Diagnosis==
Differentiation from plantar fasciitis is not always straight forward. MRI can be helpful.
Differentiating Plantar Fasciitis and Baxter Nerve Entrapment.
Feature 	Baxter Nerve Entrapment 	Plantar Fasciitis
Timing 	Pain worse after activity and night 	"First step" pain. Worse first thing in the morning and after a period of inactivity
Walking 	Worse with walking 	Better with walking
Pain type 	Neuropathic pain 	Nociceptive pain
Tenderness 	Medial calcaneal tuberosity, radiates to medial ankles and/or lateral foot	Insertion of plantar fascia at medial calcaneal tuberosity and along the medial edge where the fascia may feel thickened.
Heel pad sensation 	Equal to contralateral side 	Equal to contralateral side
Modifed from Trescot et al.	Modifed from Trescot et al. 	Modifed from Trescot et al.
If the patient has back pain then consider L5 or S1 radicular pain and examine for radiculopathy (See Lumbar Radicular Pain).
If the patient has bilateral heel pain then consider a rheumatologic origin.
Baxter nerve has no cutaneous sensation, and so if there is sensory change then medial calcaneal nerve entrapment is more likely.
In tarsal tunnel syndrome the entrapment and tenderness is more proximal.
==Investigations==
===Diagnostic Injection===
Injecting the baxter nerve can't differentiate between plantar fasciitis and baxter nerve entrapment.
===Imaging===
On MRI in the acute phase there is decreased T1 signal intensity and increased T2 signal intensity with fat saturation in the muscles innervated by the Baxter nerve. In the chronic phase there is fatty change of the abductor digiti minimi muscle, and occasionally the Flexor Digitorum Brevis and Quadratus Plantae.
Ultrasound can show a thickened and hypoechoic plantar fascia. This doesn't rule out Baxter nerve entrapment because a thickened plantar fascia can entrap the nerve.
==Treatment==
The nerve can be injected with corticosteroid and/or hydrodissected under ultrasound guidance.
==External Links==
Baxter's Nerve (First Branch of the Lateral Plantar Nerve) Impingement - Radsourcethumb|Baxter nerve injection.Baxter's nerve Sd. Procedure: corticosteroid injection & orthotics. Good result. @Dr_Ramon_Balius #MSKUltrasound pic.twitter.com/ED9RcmqJnz
==References==
Category:Foot and Ankle Conditions
Category:Mononeuropathies