Baxter's nerve is another name for the inferior calcaneal nerve, which is a nerve branch which runs beneath the heel bone. Donald Baxter, MD, an orthopedic surgeon from Houston identified entrapment of this nerve branch as a potential cause of heel pain. Baxter's neuritis or Baxter's nerve entrapment may cause heel pain which can be confused with plantar fasciitis but there are some differences in the type of symptoms each causes.
Plantar fasciitis causes heel pain that is often worse after rest or after getting out of bed, also know as "first step" pain. A medical term for that is "post-static dyskinesia." Patients with Baxter's neuritis often do not experience first step pain but experience pain that seems to gradually worsen with weight bearing activities throughout the day.
Heel pain caused by plantar fasciitis generally subsides when one sits down and at night. Heel pain due to Baxter's neuritis may continue after one is off the feet. A burning pain may be encountered or a sharp shooting pain. Patients occasionally locate the pain at the edges of the heel, either the outer or inner edge.
Treatments which are typically effective for plantar fasciitis appear to have only mild effect on Baxter's neuritis.
Baxter's nerve enters the heel at a spot at the inside of the heel which when pressed, can send a shooting pain through the heel. There is no specific test for Baxter's neuritis so the diagnosis is often made clinically. The nerve may appear enlarged or swollen upon imaging by high resolution diagnostic ultrasound. Another way to help confirm the diagnosis is for the physician to numb the nerve with a very small amount of lidocaine, preferably with the help of diagnostic ultrasound. If the numbing completely resolves the heel pain, that is a strong piece of evidence that Baxter's neuritis is present.
Treatment options for Baxter's neuritis include the "Baxter procedure" which is a surgical nerve release of the nerve or neurolysis. "Neurolysis" here refers to a means by which the nerve can be desensitized to the extent that symptoms are resolved. Two means of neurolysis are commonly used: chemical and radiofrequency lesioning.
Chemical neurolysis involves injection of the nerve with a chemical, generally a dilute solution of alcohol which desensitizes but does not "kill" the nerve. Nerves are composed of different types of fibers: motor and sensory. The sensory fibers include fibers that transmit sensations of pressure, temperature and pain. The pain fibers are termed "type C unmyelinated" fibers. Myelin is the insulation around nerve fibers but pain fibers are "uninsulated" and thus the most sensitive. As such, use of a dilute solution of alcohol injected around the nerve can selectively treat the pain fibers. Such injections require considerable accuracy as the nerve is a small target and thus need be performed under imaging such as diagnostic ultrasound or sonography. Only a very small amount can be injected at a time so the procedure need be repeated. Typically 3 to 5 such injections at two week intervals.
Radiofrequency ablation refers to the use of an instrument commonly used to treat painful spinal nerves or facial nerves in conditions such a trigeminal neuralgia. Here is a link to a manufacturers' website: http://www.cosmanmedical.com/
Radiofrequency ablation involves the accurate placment of a very thin probe that looks like a hollow needle into the area of the nerve to be treated. Placement of the probe is verified by ultrasound or fluoroscopic guidance. A very mild current is then generated and the nerve stimulated twice. The first type of stimulation is sensory stimulation in which the patient will note a recreation of the type of symptoms experienced. The second type of stimulation is motor stimulation which a lower frequency current is applied which activates the one motor branch of Baxter's nerve, the nerve to the fifth toe. One can observe the 5th toe gently move or flex. So there is triple verification of accurate placement of the probe: imaging (ultrasound or fluorscope), sensory stimulation and motor stimulation. Next the radiofreqency current is activated an the nerve heated to about 80 degrees C or 170 degrees F for a little over a minute, just enough to deactivate the sensitive pain fibers.
Relief is often immediate and the patient leaves the office or outpatient surgicenter with a bandaid and standard shoegear. Unlike chemical neurolysis, radiofrequency ablation only need be applied in one treatment.