Can Orthotics Have An Impact On Tarsal Tunnel Syndrome?

Dianne I. Mitchell, DPM, and Paul R. Scherer, DPM

   In the office, the primary author has found the best control and reduction of pain with activity modification and the use of either a walking boot or lace-up ankle brace to control hindfoot position with the addition of a heel lift. These patients tend to present not only with a positive Tinel’s sign on percussion of the nerve with burning and/or numbness but also pronation or a valgus resting calcaneal stance position and equinus. Some will also have sinus tarsi impingement and pain, but all require mechanical correction of the hindfoot and bracing helps significantly in this population in the primary author’s office. For these patients, there is subsequent progression to functional foot orthotics with the primary goal of maintaining decreased tension on the neurovascular bundle in addition to mechanically controlling the feet. This decreases pain and slowly allows patients to ease back into and increase their activities.

Assessing The Role Of Functional Foot Orthoses

Using this information on tarsal tunnel syndrome, we can incorporate what the literature says about increased compartment pressures and increased pain in the dorsiflexed and everted (or pronated) position to determine if functional foot orthotic devices may be a viable treatment option.

   Trepman found the highest tarsal tunnel compartment pressures when the foot was stressed into full eversion, which is why functional foot orthotics might be successful in reducing pain.10 Kinoshita found that placing the foot into dorsiflexion-eversion, a pronated position, and applying stress for 10 seconds elicited pain reproduction in patients with tarsal tunnel syndrome nearly 100 percent of the time.9

   Considering that the goal of functional foot orthotics is to hold the foot out of maximal pronation and instead in subtalar neutral, this again favors usage of these devices in treating painful tarsal tunnel syndrome. Based on this, it seems logical to assume that a custom-molded functional foot orthotic would be a successful treatment option. Functional foot orthotics are designed to hold the hindfoot in a neutral position and the literature does point out conservative care treatment options of casts, walking boots, and ankle braces all in order to hold the hindfoot neutral to control pain.5

Keys To Writing Orthotic Prescriptions For Tarsal Tunnel Syndrome

When writing the orthotic prescription for a patient with tarsal tunnel syndrome, the goal is to position the foot out of maximal pronation and into subtalar joint neutral in order to reduce tension on the nerve and diminish pain.2 This requires a wide device in order to get as much surface area as possible under the foot to effect this change. This occurs with semi-rigid polypropylene, which will not deform under load but instead offer continuous support to the foot. The polypropylene thickness should be based on the individual patient’s body weight.

   Polypropylene has certain advantages over other shell materials. It is lightweight and one can mill or stretch it to the desired thickness without being brittle. Unlike other plastics, it does not lose its shape or deform under load. Also, by getting the correct thickness, polypropylene allows you to get the right combination of rigidity and flexibility, and it is easy to adjust in the office to fine-tune for patient comfort.

   In addition, prescribe minimal arch fill to minimize lengthening of the longitudinal arch, which would have otherwise placed tension on the nerve. We also recommend a deep heel cup and medial heel skive in order to better control the hindfoot, or more specifically, calcaneal eversion.

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