A Closer Look At Heel Pain And Baxter’s Neuritis

Through my 23 years of practice, I often think of the old adage, “When you hear hoof beats, think horses, not zebras.” I consider myself a very good diagnostician. I base my diagnoses on comprehensive history and physical examination. However, there are times when the patient is not progressing as expected and those “hoof beats” are actually zebras. One such case is heel pain from Baxter’s neuritis, which is entrapment of the first branch of the lateral plantar nerve.

The literature on heel pain consistently notes that about 85 percent of the cases will respond to conservative care.1 When it comes to unresponsive cases, one should consider the possibility of Baxter’s neuritis prior to proceeding with any more invasive therapies.

Baxter’s neuritis typically occurs where the nerve takes a right angle turn from the medial aspect of the calcaneus. It travels laterally across the plantar aspect of the foot to the abductor digiti minimi muscle anterior to the plantar tubercle of the calcaneus. The nerve travels between the abductor hallucis and quadratus plantae muscles along the medial aspect of the calcaneus. It then turns around, traveling across the plantar aspect of the foot between the flexor digitorum brevis and quadratus plantae muscles approximately 0.5 cm anterior to the plantar calcaneal tubercle. The nerve terminates at the abductor digiti minimi muscle, which it innervates.

Practitioners should consider this diagnosis when heel pain is not responding to standard conservative measures.

Specific symptoms for Baxter’s neuritis include:
• No morning pain but pain towards the end of the day
• Paresthesias across the plantar aspect of the heel laterally
• Pain on palpation of the medial heel along the course of the nerve between the abductor hallucis and quadratus plantae muscles

One can most accurately confirm this diagnosis through magnetic resonance imaging (MRI), which shows increased water signal and fibrofatty changes of the abductor digiti minimi muscle, indicating atrophy.

The non-surgical approach to Baxter’s neuritis is similar to that of plantar fasciitis. The difference is that often the non-surgical approach for Baxter’s neuritis is not as predictable as that for plantar fasciitis. Utilize the standard external support via strappings and orthoses, equinus stretching via bracing, and inflammation reduction in the conservative treatment of Baxter’s neuritis. If symptoms persist, one may give a steroid injection at the painful point of palpation along the medial aspect of the calcaneus. Due to the entrapment neuropathy associated with this condition, it is typically minimally responsive to conservative therapy.

The surgical approach I utilize is similar to the approach that Baxter originally described.1 It consists of making an incision along the course of the nerve at the medial aspect of the heel extending to the plantar surface and traveling laterally just anterior to the weightbearing surface of the calcaneus approximately halfway across the heel. I then carry the dissection down to the deep fascia of the abductor hallucis muscle belly, which I release in a circumferential manner. I proceed to release the flexor retinaculum overlying the neurovascular bundle to at least the medial malleolus.

I proceed to perform a plantar fasciectomy, removing a section of plantar fascia without violating the lateral band of the plantar fascia in order to lessen lateral column pain due to pronatory changes. I will retract the abductor hallucis muscle dorsally while retracting the flexor digitorum brevis muscle laterally to expose the course of Baxter’s nerve. One should carefully release any adhesions along the course of the nerve. It is not necessary to see the nerve. Often, one can only see the venae comitantes. It is very important to avoid injuring the veins as this will cause bleeding that results in increased postoperative fibrosis and scarring. Recently, I have been using amniotic membrane (Amniox Medical) and placing it over the neurovascular bundle beneath the abductor hallucis muscle belly. Lastly, I will close the incision with 4-0 nylon sutures.

Postoperatively, the patient is weightbearing in a cast boot for five weeks with sutures removed at two weeks. After five weeks, the patient can transition into a gym shoe without using a custom orthosis. At approximately eight weeks, the plantar scar tissue has time to remodel. The patient can return to normal activity with physical therapy as needed. Baxter’s study showed 85 percent good to excellent results.1 Comparable patient results are realistic with adherence to the surgical technique.

References
1. Baxter DE, Pfeffer GB. Treatment of chronic heel pain by surgical release of the first branch of the lateral plantar nerve. Clin Orthop Relat Res. 1992; (279):229-36.
2. Baxter DE, Thigpen CM. Heel pain--operative results. Foot Ankle. 1984;5(1):16-25.
3. Goecker RM, Banks AS. Analysis of release of the first branch of the lateral plantar nerve. J Am Podiatr Med Assoc. 2000; 90(6):281-6.
4. Schon LC, Glennon TP, Baxter DE. Heel pain syndrome: electrodiagnostic support for nerve entrapment. Foot Ankle. 1993; 14(3):129-35.
5. Henricson AS, Westlin NE. Chronic calcaneal pain in athletes: entrapment of the calcaneal nerve? Am J Sports Med. 1984; 12(2):152-4.
6. Chundru U, Liebeskind A, Seidelmann F, Fogel J, Franklin P, Beltran J. Plantar fasciitis and calcaneal spur formation are associated with abductor digiti minimi atrophy on MRI of the foot. Skeletal Radiol. 2008; 37(6):505-10.