Has Intraoperative Nerve Testing Reinvented Our Approach To Tarsal Tunnel And Nerve Surgery?

Bob Baravarian, DPM

   Nerve surgery, especially tarsal tunnel surgery, has been very difficult to perform. More often than not, it is a poorly used treatment in foot and ankle care. Often, the diagnosis is difficult to make and surgical treatment may not result in the best outcomes if physicians have not emphasized careful patient selection.

   To date, the most common workup for tarsal tunnel and other peripheral nerve problems has been a nerve conduction test (NCV) with or without an electromyelogram (EMG). Both of these tests have shown moderately good potential in the upper extremity but have been very poor in the diagnosis of lower extremity nerve problems.

   In a personal conversation with A. Lee Dellon, MD, one of the experts in peripheral nerve work, I have noted that in most cases of positive EMG and NCV tests, the nerve is nearly burned out and has little to no chance of improvement with surgery. Basically, EMG and NCV tests have a very high rate of false negatives and, in the rare case of a positive reading, the nerve may be too far gone for an adequate outcome.

   The newest form of testing to gain popularity in foot and ankle peripheral nerve surgery is neurosensory testing. The form of one- and two-point discrimination with the Pressure Specified Sensory Device (PSSD) allows very early diagnosis of peripheral nerve alterations and has been an excellent source of information in the early care of peripheral nerve problems. Although the PSSD test is a dramatic improvement over EMG and NCV testing, it is patient driven and does take a careful technologist to detect when a patient is pressing the button without actually feeling the proper sensation.

   With the improvement in all types of foot and ankle care, nerve surgery is still a very difficult area when it comes to proper imaging and diagnostic testing is still limited. Accordingly, the diagnosis is often a process of elimination or a clinical diagnosis. Physicians often confuse tarsal tunnel syndrome symptoms with plantar fascia pain, posterior tibial pain and even possible tendonitis of the arch.

Key Findings That May Raise Suspicion Of Neuritis Or Nerve Compression

   However, in chronic cases, certain findings that emerge from a proper history and physical exam are very helpful. Patients will often complain of pain in shoes or with exercise. Patients may also note discomfort with orthotics or arch supports as the devices may press on the nerve in the area of the raised arch. They often note tingling and radiating pain.

   In regard to the common peroneal nerve at the fibular head, patients often note a weakness of dorsiflexion and/or eversion. Patients will also note tingling of the dorsum of the foot and leg with or without lateral leg and foot pain. One of the best clinical guides to nerve entrapment is a positive Tinel of the associated nerve. If one follows a patient for a period of time and he or she continues to have a tingling of the nerve with pain along the course of the nerve with tapping of the nerve in the area of potential entrapment, a neuritis or nerve compression is often present.

   In such cases, our workup proceeds to diagnostic imaging of the site for a potential mass or lesion. One may utilize either diagnostic ultrasound or magnetic resonance imaging (MRI). Furthermore, physicians may order bloodwork to screen for potential arthritic conditions, vitamin deficiency, lead poisoning and medication toxicity. Finally, one should review the patient’s medication history and check for potential systemic causes of nerve irritation.

   Subsequent to all of this testing, many patients still have no underlying cause for their nerve pain other than mechanical entrapment or neuropathic entrapment. In such cases, one may use a PSSD test to diagnose the level of nerve damage and its location. Often, a case of suspected unilateral tarsal tunnel also seems to affect the other tested nerves. This suggests a potential neuropathic problem, which may require further systemic workup.

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