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. There is little place for sharp dissection in peripheral nerve surgery, especially when it comes to tarsal tunnel decompressions. Using blunt Steven’s tenotomy scissors, one can carefully spread the subcutaneous tissues apart without damaging the nerves. You’ll often find that a medial calcaneal nerve branch can run right through the fatty tissues and there is no way to spare that nerve with sharp dissection. Once you are down to the flexor retinaculum, you must be extremely careful as the neurovascular bundle is just below. Again, if you employ the aforementioned surgical technique, you minimize the risk of damage to these structures. It is important to note this anatomical area is rarely the site of true entrapment. However, it is imperative to complete the dissection of this portion of the posterior tibial nerve as it allows you to see the origin of the medial calcaneal nerve or nerves. This also gives you the ability to identify the proximal portion of the medial and lateral plantar nerve tunnels. You will almost always find large veins in and around the posterior tibial nerve. Keep in mind that these should rarely, if ever, be ligated.6 Identify the superficial fascia of the abductor hallucis muscle and incise it without damaging the underlying muscle belly. Proceed to retract the muscle plantarly. Doing so will expose the deep fascia of the abductor hallucis muscle. This fascial tissue forms the roof of the medial and lateral plantar tunnels, and acts as the termination of the septum, which separates the medial and lateral neurovascular bundles. You must remove this septum and divide the fascial roof, which will allow for adequate decompression. Determine if there has been an adequate release by passing a finger into the area. You shouldn’t notice any tightness and you should be able to pass your finger into the plantar aspect of the arch of the foot. With this stage of the procedure complete, proceed to identify the medial calcaneal nerve tunnel or tunnels, and decompress these, alleviating any distal compression on the nerve.7 Key Tips For Closing Tarsal Tunnel Incisions Closure of the tarsal tunnel incision is very important and failure to pay close attention to this step can lead to disastrous consequences. We have found that by using intradermal 5-0 Monocril suture in an interrupted manner with the knots buried deep and combining this with surgical staples makes for an ideal skin closure. Since adopting this method of closure, we have seen no wound dehiscence, which may be the most frequent complication of the surgery. By dorsiflexing the foot at the time of skin closure, we have also noted better cosmetic results. How To Ensure Sound Postoperative Management Proper postoperative management is essential for an optimal outcome with any type of peripheral nerve surgery. With tarsal tunnel decompression, it is imperative to move the patient immediately after surgery. All peripheral nerves slide and glide similar to tendons. If a patient is immobilized after a neurolysis/decompression, there will likely be fibrosis of the nerve with a less than optimal surgical result. With a large Robert Jones-type dressing, patients are able to bear some weight on their feet immediately with the aid of crutches or a walker. This allows for movement of the nerve in addition to the active non-weightbearing range of motion exercises that I encourage for the patient. It must be emphasized that patients cannot do too much because they could tear their incisions. Apply this bulky Jones-type compression dressing in such a manner that there is no real direct compression on the extremity. We do not want to compress something we just spent meticulous time in decompressing. However, you would apply a compressive wrap for 30 minutes after deflating the tourniquet and then remove the wrap. Emphasize partial weightbearing for three weeks with a gradual increase in pressure and activity during this time. Remove sutures or staples at three weeks. These patients usually are fully active between three and five weeks, and should be informed that they can expect the swelling to dissipate over the next three to four months. In Conclusion Surgical intervention for lower extremity peripheral nerve pathology can be positively life-changing for the patient. However, a lack of adherence to sound surgical procedures, indelicate tissue handling and a lack of surgical experience with regard to nerve tissues could lead to disastrous consequences for the patient. Dr. Burks is a Fellow of the American College of Foot and Ankle Surgeons and is board-certified in foot and ankle surgery. Dr. Burks practices in Little Rock, Ark.
References 1. Keck C: The tarsal tunnel syndrome, J Bone Joint Surg, 44A:180, 1962. 2. Mackinnon SE, Dellon AL: Surgery of the peripheral nerve, Thieme, N.Y., 1988. 3. Dellon AL: Somatosensory testing and rehabilitation, Institute for Peripheral Nerve Surgery, Baltimore, 2000. 4. Tassler PL, Dellon AL: Pressure perception in the normal lower extremity and in tarsal tunnel syndrome. Muscle Nerve 19:285-289, 1996. 5. Weber RA, Schuchmann JA, Albers JH, Ortiz J: Prospective blinded evaluation of nerve conduction velocity versus pressure-specified sensory testing in carpal tunnel syndrome. Plastic and Reconstructive Surgery 436(3):252-257, 2000. 6. Mackinnon SE, Dellon AL: Homologies between the tarsal and carpal tunnels: Implications for treatment of the tarsal tunnel syndrome. Contemp Orthop 14:75-79, 1987 7. Dellon AL, Kim J, Spaulding CM: Variations in the origin of the medial calcaneal nerve. JAPMA, Vol. 92, #2, 2002.