A Closer Look At Foot Orthoses For Chronic Ankle Instability

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Author(s): 
Douglas Richie, Jr., DPM, FACFAS, FAAPSM

   Full-length top covers with medium thickness foam are preferred. These will allow more contact surface area to the sulcus and toe sections of the foot for enhanced sensory feedback. Also, full-length extensions allow for application of sulcus wedging, which one can add later later to enhance control.

   A medial arch flange will enhance stability for the patient with chronic ankle instability in almost every case. This may be a surprise to many practitioners. The use of medial flange has traditionally reduced pronation and encouraged supination of the foot. This would seem contraindicated for the patient with chronic ankle instability. However, the opposite is true. A lateral flange on a foot orthosis will resist abduction and may force the foot to invert, which will exacerbate the symptoms of lateral foot and ankle instability. Conversely, a medial arch flange will act as a blocker to foot inversion and increase the total contact surface area of the orthosis.

   When implementing foot orthotic therapy for the patient with chronic ankle instability, I recommend starting with an intrinsically balanced orthotic shell, which has no rearfoot posting. In most cases, the patient will report improved confidence in gait, balance and comfort. Unless one observes significant alignment or balance issues, further modification of this device is not necessary.

   In the event the patient is not improving, one can apply further posting or enhancement of the device in the office setting. Foot orthoses have demonstrated an ability to decrease strain on soft tissue structures around the ankle and hindfoot.28 With wedging or posting of these devices, changes in moment or torque at the ankle and subtalar joints can reduce strain of the ligaments that resist these forces. The posting material in the office setting can include various thickness of felt, Korex or ethyl vinyl acetate (EVA) foam. In all cases, apply the posting to the anterior edge (forefoot posting) of the device. Only a forefoot post can invert or evert the entire orthosis. If a patient with a mobile, pronated flatfoot deformity has a significantly pronated gait, apply a forefoot varus post. Similarly, if the patient still ambulates inverted in the hindfoot, I suggest application of a forefoot valgus post, starting with 1/8-inch Korex wedging.

   Wedging or posting of orthoses for patients with chronic ankle instability will not predictably improve postural control. Kakihana and colleagues showed that lateral wedging will shift the center of pressure laterally in both healthy people and patients with chronic ankle instability, but there may be diverse and sometimes reversed effects.32,33 Therefore, while many patients with chronic ankle instability have a laterally deviated center of pressure in stance, application of wedging laterally will only further increase this deviation.

   A novel and unscientific method of fine-tuning a foot orthosis for improvement of balance is to use the single leg stance test for stability. Ask the patient to stand on both orthoses, placed on the floor outside the shoe. The patient then stands on one foot at a time, balancing for at least 20 seconds while the practitioner observes for body sway and compensation. If body sway predominates to the lateral side, place a forefoot valgus or lateral wedge under the orthosis. This usually occurs in 1/8-inch increments with Korex material until the patient feels more secure or the practitioner observes reduced sway. Similarly, place a varus or medial wedge under the orthosis when sway is predominately medial. Ask the patient to give feedback regarding any improvement of stability with the additional posting.

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