Expert Insights On Peripheral Nerve Surgery For Tarsal Tunnel Syndrome

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By Stephen L. Barrett, DPM

Keck first described tarsal tunnel syndrome in the literature back in 1962 and it remains a controversial topic today.1 While tarsal tunnel syndrome is a prevalent and common condition, lower extremity peripheral nerve entrapments and other nerve pathology can be clinically difficult to appreciate and understand. Needless to say, making a decision to proceed with surgical intervention for this condition can also be difficult. Experienced practitioners with a high degree of neurological understanding and appreciation for peripheral nerve pathology are more likely to focus on these problems early in the course of the disease. The patient may have precise symptoms such as a history of numbness or burning into the plantar aspect of the foot, and/or pain over the course of the distal bifurcation of the posterior tibial nerve. However, you’ll often hear the patient convey more abstract symptoms or symptoms that could be attributed to another condition like heel pain. Indeed, the patient may present with “classic” plantar fasciitis, which often turns out to be a multiple etiology heel pain syndrome (MEHPS), with components of both plantar fasciitis and neural involvement either of the medial plantar nerve, medial calcaneal nerve(s) or both. Further questioning of these patients will often reveal that they have pain at night or when they are off their feet. Increased levels of activity often exacerbate symptoms. They might also describe their condition as nothing more than a feeling of tightness in their ankle. Oftentimes, they cannot tolerate an orthotic device if they are being treated for heel pain. It’s also important to question patients about any prior trauma, like an ankle sprain or fracture, and whether they were immobilized for any period of time. During the clinical evaluation, one must palpate the posterior tibial nerve to determine if it is tender or painful. Test the contralateral side as a comparison. While you will frequently note a positive Tinel’s sign, remember that there is usually not a Tinel’s sign in early and late stages of peripheral nerve compression.2 Occasionally, you may see a palpable mass or clinically significant pitting edema. What You Should Know About Neurological Testing Neurological testing of tarsal tunnel syndrome with standard electrodiagnostic testing has frequently been disappointing. Perhaps you’ve received a “normal” nerve conduction study report back from the neurological consultation despite the patient demonstrating significant symptoms of tarsal tunnel syndrome. However, with the advent of neurosensory testing with the Pressure Specified Sensory Device (PSSD)™, that scenario would be rare.3,4 As Weber pointed out, nerve conduction velocity studies in patients with clinical carpal tunnel syndrome demonstrated an 80 percent sensitivity and a 77 percent specificity.5 Testing the same patients with the PSSD resulted in a 91 percent sensitivity and 82 percent specificity. In my estimation, when it comes to tarsal tunnel syndrome, the rate of false negatives with NCV could be as high as 50 percent. Electrodiagnostic testing is also more expensive and painful for the patient. In addition to being a much more sensitive test, neurosensory testing with the PSSD also enables you to stage the level of nerve entrapment and evaluate the success or failure of any attempted conservative modality or postoperative result. Essential Pearls For Peripheral Nerve Surgery Proper incision placement, as with any surgery, is imperative to providing the ultimate outcome in tarsal tunnel surgery. Be sure to plan the incision so you adequately address exposure to all four nerves in the medial ankle compartment. The ultimate goal in performing peripheral nerve surgery is to achieve a complete neurolysis of the nerve, eliminating any source of entrapment with minimal interruption of the sliding and gliding mechanism of that nerve postoperatively. In my opinion, meticulous dissection is imperative and requires 3.5 x to 4 x surgical loupes and bipolar cautery. When it comes to peripheral nerve surgery, one should avoid monopolar cautery as there is a cone of destruction that one cannot control. However, when you employ bipolar cautery, you can be assured there will be ideal hemostasis with no damage to adjacent tissues. Be careful not to burn the skin edges with any cautery. In my opinion, using a thigh tourniquet is mandatory.

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