Baxters Nerve Entrapment

Baxter's nerve entrapment refers to an entrapment of the calcaneal branch of the posterior tibial nerve.  Baxter's nerve entrapment is a differential diagnosis that should always be considered when treating heel pain. Although plantar fasciitis is a much more common cause of plantar heel pain, astute clinicians will always include Baxter's entrapment in a complete clinical workup for heel pain.

Baxter first described this condition in 1984. Baxter proposed that the first branch of the lateral plantar branch of the posterior tibial nerve would become entrapped in the medial heel. The entrapment would result in heel pain and numbness of the plantar aspect (bottom) of the heel.

Diagnosing Baxter's nerve entrapment requires a high degree of clinical suspicion. Clinical testing as described below (Phalen's maneuver and abductor digiti minimi testing) is not considered to be a definitive or conclusive set of tests. MRI's, nerve conduction studies and EMG studies are also limited in their ability to 'rule in' a diagnosis of Baxter's entrapment.

Treatment

Conservative treatment of Baxter's entrapment is limited. Some advocate the use of oral or injectable steroids. Orthotics may be helpful to control contributing biomechanical issues such as pronation.

Surgical release of the nerve, called external neurolysis, is the preferred method of care. The procedure is completed in a surgery center or hospital setting. External neurolysis of Baxter's nerve may be performed with a local anesthetic and sedation or with a general anesthetic. The goal of neurolysis is to identify the physical irritation or the nerve, release those strictures and allow the nerve to return to normal function. Recovery varies but typical neurolysis cases do require a period of non-weight bearing on crutches.

Other methods of treatment described in the literature include cryosurgical neurolysis, chemical neurolysis and radiofrequency ablation.  Each of these methods use cold, chemicals or heat to ablate, or destroy Baxter's nerve.  The literature does not discuss comparative success rates of these methods compared to traditional surgical neurolysis.  When comparing the safety and efficacy of each of these methods of care, you must remember that surgical neurolysis is a nerve sparing surgery where as cryo, chemical and radio frequency ablation is a nerve destructive procedure.  Therefore patients who are considering one of these methods of treating a Baxter's nerve entrapment should discussed the pros and cons of each of these methods with their doctor prior to surgery.

Due to the fact that Baxter's nerve entrapment is commonly found in conjunction with plantar fasciitis, a plantar fasciotomy is often perform in addition to neurolysis.  And for sake of clarity, surgical external neurolysis is a surgical release of one of the three branches of the posterior tibial nerve.  Surgeons will often perform a release of all three branches of the posterior tibial nerve during the course of surgery.  When all three branches are released, this procedure is called a tarsal tunnel release.  Tarsal tunnel releases are often used to treat tarsal tunnel syndrome.  Doctors will often refer to a Baxter's nerve entrapment as a partial tarsal tunnel, suggesting and isolated entrapment of the calcaneal branch of the posterior tibial nerve.

Baxter's nerve - The first branch, or often called the calcaneal branch of the posterior tibial nerve.

Tarsal - refers to the region of the rearfoot.  Tarsal bones include the calcaneus, talus, navicular and cuboid.

Tarsal tunnel - the tunnel created by the lacinate ligament and abductor hallucis muscle.  The tarsal tunnel form a canal that protects and enable entry of the posterior tibial nerve, artery and vein from the ankle to the plantar surface of the foot.

Tarsal tunnel syndrome - entrapment of one or more of the three branches of the posterior tibial nerve.  Selective entrapment of the calcaneal branch of the posterior tibial nerve is often called a Baxter's nerve entrapment.

Tarsal tunnel release - surgical release of the lacinate ligament and fibrous adhesion deep to the abductor hallucis muscle at its origin on the medial heel bone (calcaneus).

The posterior tibial nerve divides into two branches on the inside of the ankle just below the media ankle bone (medial malleolus). The two terminal branches of the posterior tibial nerve are called the medial and lateral plantar branches. Both branches descend into the foot to supply sensory and motor function to the bottom of the foot. The medial branch supplies sensation to the great toe, second and third toes. The lateral branch supplies sensation to the fourth and fifth toes.

As the medial and lateral branches descend past the ankle they take a course that leads them deep to the abductor hallucis muscle. The abductor hallucis originates on the medial aspect of the heel and extends to the great toe.
Baxter's nerve, or the first branch of the lateral plantar nerve, typically branches off of the lateral plantar nerve just proximal to the abductor hallucis muscle. As Baxter's nerve descends deeper into the foot, it passes through a portal referred to as the porta pedis or 'window to the foot'. The porta pedis is a well known location for each of the nerves that pass through this portal to become entrapped.  Additional areas of entrapment for Baxter's nerve include the region deep to the plantar fascia.

As Baxter's Nerve reaches the plantar aspect (bottom) of the abductor hallucis muscle, the nerve turns to the lateral aspect of the foot and passes anteriorly and medial to the calcaneus (heel bone). This location is known as the calcaneal tuberosity and is the location where a heel spur may form. Baxter's nerve continues laterally between the quadratus plantae and flexor brevis muscles to its' insertion into the abductor digiti minimi muscle.

The biomechanical properties that may contribute to tarsal tunnel syndrome and Baxter's nerve entrapment are poorly defined.  Pronation (flattening of the arch) may contribute to increased pressure within the porta pedis and subsequent pressure on the terminal branches of the posterior tibial nerve, including Baxter's nerve. The influence of a flat foot (pronated foot) on Baxter's nerve entrapment has not been thoroughly studied.

Nerve entrapments occur at a number of locations in the body.  Examples include carpal tunnel, nerve entrapments of the lumbar spine and tarsal tunnel syndrome.  It's not unusual that each of these specific nerve entrapments share common symptoms.  For instance, nerve entrapments often fail to respond to testing such as x-rays or MRI.  Most nerve entrapments can be difficult to diagnose and Baxter's nerve entrapment is by no means an exception to the rule.

Baxter's nerve has two nerve functions; sensory and motor function.  Sensory function refers to sensations such as light touch, vibration and the sensation of warmth vs cold.  Motor function is the ability to make a muscle function.  Let's talk a brief look at each of these two functions and how that can aid in the diagnosis of a Baxter's entrapment.

First, let's look at the sensory component of Baxter's nerve.  Baxter's nerve entrapment will not exhibit symptoms when first using the extremity. For instance, you would not expect pain with Baxter's nerve entrapment when first standing in the morning while getting out of bed. But as the day progresses, symptoms of Baxter's nerve entrapment will become more pronounced. Sensory symptoms may include numbness of the bottom of the foot or a dull ache of the bottom and lateral aspect of the heel.

Baxter's nerve supplies motor innervation to the abductor digiti minimi muscle. The function of the abductor digiti minimi muscle is to abduct or pull the little toe away from the fourth toe. In extreme cases of Baxter's Nerve entrapment, the motor function of the abductor digiti minimi muscle may be compromised. This test can be misleading due to the fact that many patients do not have the ability to abduct the little toe at all.

Another test used to diagnose Baxter's nerve entrapment is called a Phalen's maneuver. A Phalen's maneuver is performed as follows; the foot is plantar flexed and inverted. The porta pedis is palpated to elicit pain and paresthesia (numbness). A positive Phalen's maneuver results in pain in the region of Baxter's nerve. Phalen's maneuver has not proven to be particularly reliable in clinical testing but is often described in the literature.

Calcaneal stress fracture
Plantar fasciitis
Tarsal tunnel syndrome
Rheumatoid Arthritis
Reiter's Syndrome
Sever's Disease

• Heel Pain

• Plantar Fasciitis

• Tarsal Tunnel Syndrome

• Equinus

• CT Band Syndrome

This article was written by Jeffrey A. Oster, DPM and last updated 2/5/13.

1. Baxter DE, Thigpen CM: Heel Pain-operative results. Foot Ankle 5: 16, 1984

2. Baxter DE, Pfeffer GB: Treatment of chronic heel pain by surgical release of the first branch of the lateral plantar nerve. Clin Orthop 279: 229, 1992

3. Baxter DE: Release of the nerve to the abductor digiti minimi, in Master Techniques In Orthopedic Surgery Of The Foot And Ankle, ed by HB Kitaoka.

4. Sarrafin SK: Nerves in Anatomy Of The Foot And Ankle,p 381, JB Lippincott, Philadelphia, PA, 1993.

5. Kenzora JE: The painful heel syndrome: an entrapment neuropathy. Bull Hosp Jt Dis 47:178, 1987

6. Goecker RM, Banks AS: Analysis of release of the first branch of the lateral plantar nerve. JAPMA 90; 281, 2000

7. Confitti JA, Tarquinio TA: Operative outcome of partial plantar fasciectomy and neurolysis to the nerve of the abductor digiti minimi muscle for recalcitrant plantar fasciitis. Foot Ankle Int 25: 482, 2004

8. Cione JA, Cozzarelli J, Mullin CJ: A Retrospective Study of Radiofrequency Thermal Lesioning for the Treatment of Neuritis of the Medial Calcaneal Nerve and its Terminal Branches in Chronic Heel Pain
Journal of Foot and Ankle Surgery March 2009 (Vol. 48, Issue 2, Pages 142-147)