Working Diagnosis:
Tarsal tunnel syndrome and Baxter nerve entrapment.

Treatment:
This patient underwent a surgical tarsal tunnel release and release of the entrapment of Baxter's nerve.

Outcome:
Following the soft tissue releases, the patient improved immensely with complete resolution of his pain within a week. The patient was subsequently referred to physical therapy to strengthen the arch of the foot and calf muscles. More recently, the physical therapist initiated dry needling in hopes of increasing the ankle flexibility. Orthopedic surgery cleared the patient to begin training in football twelve weeks after surgery and he has done well since.

Author's Comments:
The tarsal tunnel ceiling is comprised of a flexor retinaculum that spans from the medial malleolus to the medial calcaneal process. The tarsal tunnel floor is comprised of the calcaneus, tibia, and talus. This tunnel contains the tibialis posterior tendon, flexor digitorum longus tendon, flexor hallucis longus tendon, and the posterior tibial artery/nerve/vein (Mnemonic: Tom Dick and Very Nervous Harry).
Tarsal tunnel syndrome occurs when the posterior tibial nerve is compressed as it courses through the tarsal tunnel. The dorsiflexion-eversion test is positive in 82% of patients with tarsal tunnel syndrome. It is performed by passively dorsiflexing and everting the ankle to the end of the range of motion and holding for 10 seconds.
An MRI is typically non-diagnostic but can be used to rule out differential diagnoses. Specifically, in chronic Baxter nerve compression, there will be muscle atrophy of the abductor digiti minimi due to the longevity of compression.
Baxter's nerve is the first branch of the lateral plantar nerve, also known as the inferior calcaneal nerve.
EMG/NCS tests are sometimes abnormal, with sensory conduction deficits more commonly seen than motor nerve conduction deficits but with poor sensitivity and specificity.
Tarsal tunnel nerve blocks can be used to diagnose and treat tarsal tunnel syndrome.
A detailed history, exam, and diagnostic testing will be needed to help delineate tarsal tunnel syndrome versus other nerve entrapments, including Baxter's nerve and the medial calcaneal nerve. Specifically, in medial calcaneal nerve entrapment, the patient would not experience pain distal to the calcaneus.

Editor's Comments:
The first branch of the lateral plantar nerve, Baxters nerve, runs underneath the abductor hallucis muscle between and the quadratus plantae. It then courses under the medial calcaneal tuberosity before terminating at the abductor digiti minimi. The two most common entrapment locations are at the distal edge of the fascia of the abductor hallucis muscle and the medial aspect of the medial calcaneal tuberosity. In athletes, hypertrophy of the abductor hallucis muscle can increase the risk of entrapment thus is commonly seen in running sports.

The diagnosis of Baxters nerve entrapment is clinical. This pain has a burning characteristic rather than a sharp pain in plantar fasciitis. In addition, pain is worse in the evening or after activity, whereas planar fasciitis pain occurs in the morning or after a prolonged period of rest.

References:
Conti, M, Walters, D, O Malley, M. Plantar Fasciitis: Distal Tarsal Tunnel (Baxters Nerve) in the Athlete. Operative Techniques in Sports Medicine, 2021;29(3).

Ahmad, M, Tsang, K, Mackenney, PJ, Adedapo, AO. Tarsal tunnel syndrome: A literature review. Foot and Ankle Surgery. 2012;18(3)149-152.

Ferkel E, Davis WH, Ellington JK. Entrapment Neuropathies of the Foot and Ankle. Clin Sports Med. 2015;34(4):791-801.

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