Keys To Detecting And Treating Entrapment Neuropathies

Author(s): 
Jodi Schoenhaus, DPM, and Jason Gold, DPM

   Radiographs and magnetic resonance imaging (MRI) will only be helpful to rule out other pathologies. In one prospective study, researchers found that MRI revealed fatty atrophy of the abductor digiti quinti in only 7 percent of patients with nerve entrapment related symptoms.4 An electromyography/nerve conduction velocity (EMG/NCV) study may be beneficial. However, it is crucial that the physician perform the test under dynamic conditions. In regard to the standard EMG/ NCV test, the patient is usually non-weightbearing and the static study may present a false negative outcome.

Can Conservative Care Have An Impact?

   Conservative therapy consists of: a short course of oral anti-inflammatory medication; padding and offloading of the entrapment site; steroid injection therapy; stretching exercises; and physical therapy. Physical therapy is beneficial if the patient has concurrent entrapment of Baxter’s nerve and plantar fasciitis.

   Orthotic management and control may be beneficial. However, orthotics often exacerbate symptoms. Vertical ground/orthotic reaction forces against an entrapped site lead to further compartment compression and burning pain ensues.

Emphasizing The Benefits Of Preoperative Planning

   When attempted conservative therapy fails, surgical intervention is warranted. It is recommended to perform a medial band plantar fascial release in conjunction with Baxter’s nerve release. If tarsal tunnel syndrome is present, one must address this condition as well. A clear differential is necessary as Baxter’s nerve entrapment can cause referred pain in the tarsal tunnel but isolated tarsal tunnel entrapment may not be present.5

   Preoperative incision planning is essential. Patient feedback, palpation of the artery and marking the incision preoperatively will allow for visualization of all pertinent structures. Ask the patient to identify the site of intense pain and mark the entrapment area with an “X.”

   Proceed to identify the posterior tibial artery. The tibial nerve will lay just posterior to the artery. For a complete tarsal tunnel release, start the incision roughly 3 cm proximal to the medial malleolus and halfway between the medial border of the Achilles tendon and the medial malleolus.

   The tibial nerve courses distally and will bifurcate at the level between the medial malleolus and the calcaneus. Follow this distally to the site of the “X.” Extend the incision distally over the medial border of the anterior calcaneus. Preoperative identification of the medial calcaneal nerve through percussion will not only prevent unintentional neurectomy but helps to identify a crucial area of surgical release.

Pertinent Pearls On Performing Appropriate Releases

   Ensure the patient is in a supine position and apply a thigh tourniquet. Flex the hip and ensure it is externally rotated while the knee is flexed. This allows direct visualization to the medial ankle and foot.

   In order to only address the Baxter’s nerve and the medial plantar fascia, make a medial linear incision from the proximal plantar aspect of the abductor hallucis to the anterior level of the medial calcaneal tubercle. This incision is anterior to the medial calcaneal nerve. The surgeon should not encounter the medial calcaneal nerve but be aware of the anatomical variation of other calcaneal branches.

   Deep to the subcutaneous tissue lies the superficial abductor fascia, which you can proceed to release. Retraction of the abductor hallucis muscle superiorly will allow for release of the thick deep fascia of abductor hallucis and medial border of the quadratus plantae. An adequate release will liberate Baxter’s nerve from entrapment at this site.

   Proceed to perform a partial fasciotomy of the medial one-third of the plantar fascia. If a spur is present, perform an exostectomy but take care to avoid damage to the nerve coursing anteriorly or laterally.

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