By Jeffrey A. Oster / Published on March 26th, 2007 / Health & Medical
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. 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 is not particularly conclusive. MRI's 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 neurolysis, is the preferred method of care. The procedure is completed in a surgery center or hospital setting. 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.
Due to the fact that Baxter's nerve entrapment is commonly found in conjunction with plantar fasciitis, a plantar fasciotomy is commonly perform in addition to neurolysis.
Anatomy:
The posterior tibial nerve divides into two branches on the inside of the ankle just below the inside 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.
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.
Biomechanics:
Pronation 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.
Symptoms:
Nerve entrapment pain can be difficult to diagnose and Baxter's nerve entrapment is by no means an exception to the rule. In most cases of nerve entrapment, pain will not be present 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 would become more pronounced. 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.
Differential Diagnosis:
Calcaneal stress fracture
Plantar fasciitis
Tarsal Tunnel Syndrome
Rheumatoid Arthritis
References:
Baxter DE, Thigpen CM: Heel Pain-operative results. Foot Ankle 5: 16, 1984
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
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.
Sarrafin SK: "Nerves" in Anatomy Of The Foot And Ankle,p 381, JB Lippincott, Philadelphia, PA, 1993.
Kenzora JE: The painful heel syndrome: an entrapment neuropathy. Bull Hosp Jt Dis 47:178, 1987
Goecker RM, Banks AS: Analysis of release of the first branch of the lateral plantar nerve. JAPMA 90; 281, 2000
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
About the Author
Jeffrey A. Oster, DPM, C.Ped is a board certified foot and ankle surgeon. Dr. Oster is also board certified in pedorthics. Dr. Oster is medical director of