Baxter Neuropathy with Chronic Plantar Fasciosis

Chronic Heel Pain in 60F • Xray of the Week 2016 • Week #48

This 60 year old female has chronic heel pain and lateral heel numbness. What is the diagnosis?

Figure 1A. Sagittal T1 weighted image demonstrates fatty atrophy of the abductor digiti minimi muscle (yellow arrow) consistent with chronic inferior calcaneal nerve (Baxter’s nerve) denervation.

Figure 1B. Sagittal PD fat sat image showing severe plantar fasciosis, extensive partial tear (yellow arrow), spur, and reactive calcaneal osteitis.

Figure 2A.. Coronal PD fat sat image showing fatty atrophy of the abductor digiti minimi muscle (yellow arrow) compared to the normal musculature (blue arrow).

Figure 2B. Sagittal PD fat sat image showing plantar fasciosis with abnormal high signal in the calcaneal insertion of the plantar fascia (yellow arrow).

Figure 2C. Axial T1 weighted image showing fatty atrophy with abnormal high signal in the abductor digiti minimi muscle (yellow arrow).

Although often not recognized, Baxter neuropathy may be the elusive cause of heel pain in up to 20% of cases. The inferior calcaneal nerve which is known as Baxter nerve is almost always the first branch of the lateral plantar nerve and it provides motor innervation to the abductor digiti minimi, lateral half of the quadratus plantae, and flexor digitorum brevis muscles. The nerve provides sensation to the calcaneal periosteum, long plantar ligament, and adjacent vessels. Baxter neuropathy may be due to entrapment as the nerve passes between the deep fascia of the abductor hallucis muscle and the medial plantar margin of the quadratus plantae muscle. In this case more distal entrapment has occurred, due to plantar fascitis and a calcaneal spur as the nerve passes along the anterior aspect of the medial calcaneal tuberosity. Imaging with MR in the acute and subacute phases demonstrates edema of the abductor digiti minimi muscle with high signal on T2 weighted or STIR images. Chronic denervation leads to irreversible muscle atrophy with muscle belly volume loss and fatty replacement manifested as high signal on T1 weighted images. [Fig.1,2]

Like most neuropathies, initial treatment is conservative with non-steroidal anti inflammatory drugs, padding and offloading of the entrapment site, steroid injection therapy, and physical therapy. Surgery with medial band plantar fascial release and inferior calcaneal nerve release may be necessary in refractory cases.

References:

1. Donovan A et al. MR Imaging of Entrapment Neuropathies of the Lower Extremity Part 2. The Knee, Leg, Ankle, and Foot Radiographics 2010;30:1001-1019

2. Recht MP, Grooff P, Ilaslan H et-al. Selective atrophy of the abductor digiti quinti: an MRI study. AJR Am J Roentgenol. 2007;189 (3): W123-7.

3. Chundru U, Liebeskind A, Seidelmann F et-al. 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.

4. Dirim B, Resnick D, Ozenler NK. Bilateral Baxter's neuropathy secondary to plantar fasciitis. Med. Sci. Monit. 2010;16 (4): CS50-53.

5. Toye L. Baxter’s Nerve (First Branch of the Lateral Plantar Nerve) Impingement. http://radsource.us/baxters-nerve Accessed Nov 25,2016

6. Baxter DE. Release of the nerve to the abductor digiti minimi. In: Kitaoka HB, ed. Master techniques in orthopaedic surgery of the foot and ankle. Philadelphia, PA: Lippincott Williams and Wilkins; 2002: 359.

Phillip Tirman, MD is the Medical Director of Musculoskeletal Imaging at the Renaissance Imaging Center in Westlake Village, California. A nationally recognized expert in the applications of MRI for evaluating MSK and spine disorders, Dr. Tirman is the co-author of three textbooks, including Shoulder Magnetic Resonance Imaging and Diagnostic Imaging: Orthopedics. He is also the author or co-author on over sixty original scientific articles published in the radiology and orthopedic literature.

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Kevin M. Rice, MD is the President of Global Radiology CME

Dr. Rice serves as the Chair of the Radiology Department of Valley Presbyterian Hospital in Los Angeles, California and is a radiologist with Renaissance Imaging Medical Associates. Dr. Rice has made several media appearances and as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015 Dr. Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" award for the Most Effective Radiology Educator.

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