Plantar fasciitis is possibly the most common foot and ankle referral
diagnosis seen in the orthopedic physical therapy clinic. Patients typically
report pain in the bottom or sides of the heel that can be quite debilitating
and greatly impact daily life. While most heel referrals are likely to be
labeled at plantar fasciitis, it’s important to also consider another fairly
common condition that may be present, inferior calcaneal nerve (Baxter’s nerve)
entrapment.
The inferior calcaneal nerve is also commonly referred to as Baxter’s nerve.
Named after the physician, Dr. Donald Baxter, who first described the condition
in 1984, it is the first branch of the lateral plantar nerve. Baxter’s nerve is
a mixed motor and sensory nerve and supplies motor innervation to the abductor
digiti minimi muscle. There are three areas where the nerve can become
entrapped: deep to or adjacent to the edge of a hypertrophied abductor halluces,
along the medial edge of the quadratus plantae, and adjacent to the medial
calcaneal tuberosity. A calcaneal enthesophyte and/or soft tissue changes seen
in progression of plantar fasciitis can contribute to entrapment at the last
location.
Baxter’s nerve entrapment has been claimed to account for up to 20% of heel pain
cases. While it is common in the general population, it has also been shown to
be common with the athletic population as well. According to one study, up to
50% of cases are due to athletic activity, with it accounting for 15% of
persistent heel pain in athletes, especially long distance runners due to
hypertrophy of abductor halluces in that population. Patients with Baxter’s
nerve entrapment will commonly come in with many of the same complaints as those
with a true plantar fasciitis. In fact, the evidence shows that often the two
conditions may happen at the same time, and the nerve entrapment may increase
with soft tissue changes of the plantar fascia, at least earlier on in the
condition.
So how do we tell the difference? There are no clinical tests to successfully
rule in or out the presence of Baxter’s nerve impingement at this time, so
differential diagnosis involves paying close attention to pain details during
subjective questioning, as well as possible failure of conservative treatment of
the plantar fascia. In typical plantar fasciitis, the patient will complain of
significant pain when taking the first few steps following sleeping or after
prolonged sitting, referred to as post-static dyskinesia, as well as reduction
in pain when not weight bearing. In contrast, Baxter’s nerve impingement will
tend to demonstrate increasing pain as the day goes on and continued weight
bearing. Patients will also tend to demonstrate pain even when they are not
weight bearing with nerve entrapment. In some cases, but not all, there are
slight paresthesias present on the lateral foot. The patient may also lose the
ability to abduct the fifth digit if motor function is compromised, but that is
something for many people in the general population to do, so its usefulness in
diagnosis may be limited. Injections of lidocaine can also be used by the
physician for diagnosis, looking for relief of symptoms with small amounts
injected at the location of the nerve.
Treatment tends to be conservative in nature and includes NSAIDS, rest,
orthotics, and corticosteroid injections. If pain persists there are surgical
options, most commonly neurolysis, with or without release of any tight fascial
restrictions. Therapy is often also used to alleviate any of the ROM and
strength limitations that may have led to the initial insult.
Last revised: 8/18/16
by Bill Lyon, PT, DPT, OCS, CSCS, USAW-L1
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http://radsource.us/baxters-nerve/
