How To Address Baxter's Nerve Entrapment

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In this photo, surgeons have performed a release of the abductor fascia. One can clearly see the abductor and short flexor muscle belly. The plantar fascia is still intact.
When performing the plantar fasciectomy, the authors recommend sectioning 5 to 8 mm of both the medial and medial one-half of the central bands.
Here one can see completion of the plantar fasciectomy.
How To Address Baxter's Nerve Entrapment
How To Address Baxter's Nerve Entrapment
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Author(s): 
By Stephen Offutt, DPM, MS and Patrick DeHeer, DPM

When conducting the physical exam, one should:
   • palpate the proximal and distal plantar fascia;
   • palpate and percuss the tibial and medial calcaneal nerve;
   • palpate the abductor hallucis origin;
   • assess for pain with compression of the heel from side to side; and
   • see if engaging the windlass mechanism induces symptoms.

   By systematically gathering this information on every heel pain patient, you will have screened for all the differentials.

   Initially, Baxter’s nerve entrapment might not declare itself as a distinct entity. This is particularly true in the face of chronic plantar fasciitis cases in which adjacent fascial edema can lead to nerve entrapment. This can create a mixed or combined clinical picture.

   Classically, clinicians will note distinct, exquisite tenderness over the origin on the abductor hallucis, which can cause laterally radiating pain and/or parathesias. Many times, one can also elicit symptoms by using Phalen’s maneuver. To perform this maneuver, you invert and plantarflex the foot. This causes the porta pedis to narrow at the superior margin of the abductor hallucis and compress the nerve. You will also want to assess the patient’s ability to abduct the fifth digit. Some patients lack this ability inherently so be sure to compare the affected side with the contralateral side. If Baxter’s nerve entrapment is present, the patient may not be able to abduct the fifth digit. Clinically, we have not found this to be a reliable indicator. Patients with classic Baxter’s nerve entrapment often will deny first step pain but, on the contrary, will complain of symptoms worsening with prolonged activity. They may also complain of laterally radiating pain. During the biomechanical exam, clinicians will typically note a pronated foot structure.

   Plain radiographs and bone scans can help rule out osseous pathology. If you suspect systemic arthropathy, you may employ serologic testing. Obtaining a MRI can be helpful in a couple of ways. It will determine the presence or absence of inflammation around the proximal fascia as well as fascial thickness. If you see little inflammation, you can assume the heel pain is related to nerve entrapment. Another interesting finding reported by Seidelmann is increased water signal and fatty replacement of the abductor digiti minimi, which would indicate atrophy secondary to chronic nerve entrapment.7 In our opinion, NCVs and EMG are rarely helpful in making the diagnosis.

   It has also been our experience that the classic signs and symptoms of Baxter’s nerve entrapment are often superimposed with those of plantar fasciitis. This is logical as the same pronated foot structure, which is a probable cause for Baxter’s nerve entrapment, is often the cause of plantar fascial strain and overload as well. Fortunately, the initial treatment is virtually identical for both conditions.

A Guide To Initial Treatment

   In our practice, almost all patients with plantar heel pain receive the same initial treatment. We use taping to control pathologic motion, initiate an aggressive Achilles/plantar fascia stretching program and reduce inflammation with a Medrol dose pack or, less frequently, NSAIDs. Subsequent visits incorporate combinations of plantar fascia injections, a custom orthosis, night splints and physical therapy. The majority of the patients with plantar fasciitis will respond to these treatments. We have found that although these same conservative treatments are indicated for both Baxter’s nerve entrapment and plantar fasciitis, patients with nerve entrapment traditionally have a much poorer response.

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