A Closer Look At Foot Orthoses For Chronic Ankle Instability
Recently, Gross and coworkers studied a group of older adults with a history of falls and tested the use of custom foot orthotics on several static and dynamic tests for balance.20 The authors noted improvements in balance immediately and after two weeks of use of the custom orthotic devices. Note that these orthoses were custom fabricated and posted according to the specific biomechanical findings of each patient.
Another randomized controlled clinical trial tested a custom foot orthosis prescribed to 94 elderly women with osteoporosis.21 The women who wore foot orthoses showed improvements in dynamic balance and foot pain. The researchers speculated that the foot orthoses optimized sensory information from the soles of the feet to improve proprioception and postural control.
Researchers have made attempts to study the effects of shoe inserts with textured surfaces or vibrating sources designed to enhance sensory input and improve balance. Rome and I described these studies in a previous article published in Podiatry Today.22 Currently, there is a lack of consistent evidence that textured or “enhanced” orthoses can improve sensory feedback to improve balance. Most of these studies were on healthy patients or elderly patients at risk for falling.
More recently, McKeon and colleagues studied the effects of textured insoles on patients with chronic ankle instability.23 The authors found a significant negative effect on postural control when patients wore a textured insole in comparison to a sham device. The researchers concluded that the textured surface of the insole caused a distortion or alteration feedback rather than enhanced sensory input from the sole of the foot.
How Should We Design Foot Orthoses To Treat Chronic Ankle Instability?
When prescribing foot orthoses to treat patients with chronic ankle instability, it is important to study the gait pattern of each and every patient. Besides learning about foot type and alignment of the feet during various phases of gait, the practitioner should look for evidence of lost range of motion, muscle weakness and balance deficits, all of which can become apparent during simple walking activity.
Patients with chronic ankle instability have demonstrated an alteration of walking mechanics and an inability to distribute pressure normally across the plantar surface of the foot.24 Studies have shown that patients with chronic ankle instability place greater pressure on the lateral aspect of their foot while walking.25 Schmidt and colleagues replicated this finding in runners with chronic ankle instability.26 In this study, patients also demonstrated a reduced loading or slowing down of the loading response from the rearfoot to the midfoot. These findings may indicate a weakness of the peroneal muscles to counteract the ankle invertors during gait and a possible abnormality in structural alignment, which directs loading to the lateral surface of the foot.
Postural control is compromised in both supinated and pronated foot types. A study has shown that supinated individuals had greater speed and maximal displacement in the medial-lateral direction of center of pressure than neutral individuals.27 In the same study, pronated individuals had greater maximum displacement in the anterior-posterior direction than neutral individuals. They also had a shorter single limb stance duration. The researchers concluded that individuals with pronated feet and supinated feet have poorer postural control than individuals with neutral feet, but perhaps through different mechanisms.