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How To Address And Prevent Complications With AFOs

Medial malleolar irritation and talonavicular irritation are some of the common issues that arise for patients wearing ankle-foot orthoses (AFOs). Accordingly, this author offers salient preventive advice and provides essential pearls for treating complications with functional and gauntlet AFOs when they occur.

   Over the past 15 years, ankle-foot orthotic (AFO) therapy has become an integral part of many podiatric practices. As with any DME item, there can be comfort, fit or function problems that emerge when patients use AFOs. It is imperative that the prescribing physician be adept at troubleshooting any situation that may occur.

   The most common AFOs currently in use include the functional AFO (Richie Brace type) and the gauntlet AFO (Arizona Brace type). Both of these AFOs are now commonly used in the podiatric profession for pathologies including adult-acquired flatfoot, ankle degenerative joint disease (DJD) and lateral ankle instability. Both types are available from many orthotic laboratories under several brand names.

   With this in mind, let us take a closer look at the most common complaints that patients have with AFOs.

   For functional AFOs, the common complaints are medial malleolar irritation and talonavicular (TN) irritation. For gauntlet AFOs, the most common complaints involve irritation at the collars at the proximal and distal aspects of the AFO.

A Guide To Troubleshooting Gauntlet AFOs

   Since a gauntlet AFO holds the foot in a more stable position, there tend to be fewer problems with irritation as it is less likely for pronatory forces to increase pressure on the medial malleoli and the navicular. It is fortunate that we see fewer issues with this AFO as it is much more difficult — and in most cases impossible — for practitioners to modify this AFO themselves. The brace manufacturer must make the modifications.

   The most common areas that tend to cause irritation are the collars at the proximal and distal aspects of the AFO. The most common complaint is that the collars are simply too tight. This is frequently due to edema that increases leg and foot circumference.

   To prevent this problem, try to cast patients toward the end of the day when edema is likely to be greatest. If these areas do irritate the patient, return the AFO to the lab for stretching.

   Correct casting technique is critical to achieve optimum clinical outcomes. Casting for gauntlet AFOs includes the use of a semi-weightbearing cast with a slight heel raise, maintaining the foot at 90 degrees to the leg.

Emphasizing Proper Patient Selection And Appropriate Casting Of Functional AFOs

   When prescribing functional AFOs, practitioners must take care to select appropriate patients and cast patients properly. Functional AFOs are appropriate for patients with the following conditions: severe flatfoot, arthritis of the ankle/foot, posterior tibial tendon dysfunction, ankle sprains/instability, dropfoot and/or tendonitis.

Keep in mind that functional AFOs are not appropriate for:

   • patients with equinus as their primary deformity in Achilles tendonitis;
   • patients with posterior group spasticity; or
   • patients with severe subtalar joint subluxation (i.e., late Stage 3 or Stage 4).

   Additionally, patients heavier than 250 lbs. or taller than 6’2” should not receive functional AFOs.

   However, those who are not candidates for functional AFOs may be candidates for other varieties of AFOs, including the aforementioned gauntlet AFOs.

   Correct casting for functional AFOs includes maintaining the foot at 90 degrees to the leg with the subtalar joint in neutral position, the midtarsal joint locked and the first ray plantar flexed.

Pertinent Pointers On Treating Medial Malleolar Irritation

   In some instances, a patient may receive a functional AFO but present later with medial malleolar pain due to medial displacement of the medial malleolus. Taking the following steps usually corrects the problem.

   One can perform a simple modification in the office to reshape the upright and bend it away from the prominent malleolus. Utilizing a heat gun, focus the heat on the segment just under the medial ankle pivot.

   Once the plastic is pliable, one should push the medial limb in a slightly medial direction. This is easier to do with two people. Have an assistant stabilize the AFO in an upright position while you aim the heat gun and push the limb down. Hold the position for one minute.

   The patient should wear the AFO and check for sufficient bending of the medial hinge. If irritation still occurs, one should repeat these steps as necessary.

   The medial malleolus is more likely to have medial stability if one increases pronation control and decreases calcaneal eversion. There are simple modifications that one can perform if the AFO does not initially offer enough control. Adding a “medial heel pad” is an effective modification. This pad is simply a medial heel skive which one can add to a finished orthosis with a material like Korex or EVA.

   Physicians can gauge the efficacy of the medial heel pad by adding a varus wedge to the interior of the heel cup with 1/8-inch adhesive felt. If necessary, add additional layers of felt until patients attain pain relief or until they cannot tolerate more layers of felt. If this modification decreases the symptoms, the lab can add a soft medial skive to the AFO.

   Even with extensive pronation control in the orthosis, patients with severe flatfoot may continue pronating into the AFO’s medial upright. When it comes to these patients, one can attain additional control and decrease symptoms by making shoe modifications that decrease pronation. A medial buttress and a medial flare are the most common anti-pronation shoe modifications.

   Patients wearing any type of AFO should not wear cotton socks. Acrylic socks such as Thorlo™ provide more cushioning and less friction in comparison to cotton socks.

Examining Potential Causes Of Malleolar Irritation In Functional AFOs

   There are several potential causes when it comes to malleolar irritation with functional AFOs. These causes include medial displacement of the distal tibia, incorrect hinge placement, incorrect positive cast work, improper negative casting, and a lack of shoe stability.

   Improper placement of the medial hinge is most likely if one does not appropriately mark the malleoli or if the physician uses an improper casting position. Therefore, it is always imperative to ensure that the mark on the malleoli transfers to the plaster cast. If you are using an STS Sock (STS) rather than plaster to cast the foot, mark the malleoli on the outside of the sock while the patient is still wearing it. Alternatively, placing a piece of felt over the malleoli at the time of casting permits one to capture an impression of the felt with the sock.

   Proper casting position is also of prime importance. During casting, if the ankle is plantarflexed, one may inadvertently place the hinge too far superior to the malleolus. Maintain the foot at 90 degrees to the leg while casting. A functional AFO is contraindicated for patients with an equinus that prevents the foot from reaching 90 degrees.

How To Prevent Severe Medial Displacement Of The Distal Tibia

   Severe medial displacement of the distal tibia during weightbearing is another cause of malleolar irritation. Medial displacement presses the medial malleolus into the medial upright, causing pain and pressure.

   In order to avoid malleolar irritation secondary to medial displacement, ensuring a thorough weightbearing examination is a key first step. If the weightbearing exam reveals significant tibial shifting, note it on the exam form or send the lab a picture of the patient along with the prescription. The laboratory can adjust the medial upright to fit around the malleolus.

   One should also prescribe anti-pronation control measures. These measures include a medial heel skive, minimum cast fill, medial flange and deep heel cup in the AFO’s foot portion. Such an orthosis will apply more force medial to the axis of the subtalar joint and help prevent the patient from pronating into the medial upright.

   While casting, plantarflexing the first ray can remove forefoot supinatus (forefoot varus due to soft tissue contracture of dorsal ligamentous structures). If one does not plantarflex the first ray during casting, the negative cast and the subsequent orthosis will not provide sufficient arch control. Insufficient arch control may cause the arch of the foot to collapse into the orthotic device. This can cause heel eversion with subsequent medial displacement of the medial malleolus.

   Before giving the patient the orthotic device, a close evaluation of the device is important. Excessive pronation and subsequent medial malleolar irritation can result from lab errors. For example, if the lab adds excessive arch fill to the positive cast, the resulting device’s arch will gap from the foot and allow the foot to pronate into the arch. Therefore, heel eversion and medial motion of the medial malleolus is more likely as the foot pronates.

   Another potential laboratory error is making the device too narrow. Orthotics that are too narrow will provide less control of excessive pronation.

   Patients may also exhibit incomplete balancing of the forefoot. Both the cast and orthosis will retain excessive forefoot varus if the laboratory does not completely balance any forefoot valgus found in the negative cast. Excessive varus causes a lower arch and more potential for subtalar joint pronation and subsequent displacement of the medial malleolus.

   Patients should be wearing stable shoes with torsional stability, a firm heel counter and a firm medial midsole. Contact an orthotic lab that manufactures functional AFOs to get a list of recommended shoes to dispense to patients.

Inside Insights For AddressingTalonavicular Irritation

   After receiving a prescription for a functional AFO, the patient may later complain of pain from irritation of a prominent TN joint. If this occurs, one should increase the control of pronation in both the orthotic and the shoe. Patients should wear acrylic socks to combat malleolar irritation.

   The lab can also add a sweet spot to the device by spot heating the polypropylene. It is important to ensure proper placement of the sweet spot. One should use lipstick to mark the prominent area of the patient’s foot and hold the orthosis against the patient’s foot so the lipstick transfers to the orthotic. Outline the lipstick mark with a Sharpie pen so the mark will be permanent.

   To offload the prominence, one can also add a horseshoe pad to the orthosis. This modification is especially simple if the physician prescribes topcovers to be “glued heel only.”

   Doing this enables either the physician or the lab to add the accommodation without needing to replace the topcover.

What You Should Know About Preventing Talonavicular Irritation

   Talonavicular irritation usually results from a failure to capture the weightbearing prominence of talonavicular subluxation. For these patients, the orthotic plate irritates a prominent talonavicular joint.

   This occurs as the medial flange, which is usually prescribed on devices for tibialis posterior dysfunction, wraps around the foot’s medial arch. As the foot pronates, it forces the prominent navicular into the orthotic plate, which leads to increased irritation.

   When it comes to preventing talonavicular irritation, one can employ the same techniques for preventing medial malleolus irritation. Additionally, for a patient with a talonavicular prominence, the practitioner should prescribe a sweet spot, a vacuum-formed pocket incorporated into the orthosis. The orthotic laboratory should fill the sweet spot with a cushioning material like Poron®.

   To help the lab properly place the sweet spot, mark the prominence with lipstick so it transfers to the plaster negative cast. If you are using an STS Sock, place a piece of felt over the prominence during casting so the sock captures an impression of the felt.

Dr. Huppin is the Medical Director for ProLab Orthotics/USA and in private practice in Seattle.

Editor’s note: This article is partially adapted from the article “Troubleshooting AFOs,” which appeared in the April 2005 issue of Podiatry Today.

For further reading, see “Exploring The Potential Of AFO Devices” in the January 2003 issue of Podiatry Today or “Selecting Appropriate AFOs: Key Considerations And Modifications” in the October 2003 issue.

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Lawrence Huppin, DPM
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