Patients with Charcot-Marie-Tooth disease showing the greatest increase in speed appear to respond to and utilize the energy storing and releasing properties of a carbon fiber composite ankle foot orthosis differently from those who had smaller increases in walking speed.
By Janet S. Dufek, PhD; Edward S. Neumann, PhD, PE, CP; M. Cameron Hawkins, PhD; and Brendan J. O’Toole, PhD
Charcot-Marie-Tooth (CMT) disease affects an estimated one in 2500 individuals in the US.1 The disease results in protein abnormalities in the structure and function of either peripheral nerve axons or the myelin sheaths that encase peripheral nerves. Patients with CMT often present with bilateral weakness of the muscles of the leg, which are often asymmetric in volume. Weakness is frequently progressive, with effects typically observed first in the ankle plantar flexors and dorsiflexors.2-4 CMT is one form of peripheral nerve neuropathy, among others, that affects the stability of the foot during stance, which influences not only quality of gait, but confidence in one’s ability to walk. It has been suggested that functional capacity is compromised, with social and emotional aspects of CMT patients also often neglected.
One of the approaches often prescribed for the treatment of more severe weakness is orthotic bracing, typically bilateral ankle foot orthoses (AFOs) to compensate for muscle weakness in the leg.6-12 Bracing is typically prescribed when muscular weakness progresses to the point of foot drop, which interferes with normal gait patterns. Traditional AFO braces are made out of plastic with little or no capacity for energy storage and release. They are often bulky and therefore disliked by patients.13,14 The lack of ability to store and release energy may also limit the functional assistance provided by the AFO. Therefore, our research group sought to explore the energy and storage release characteristics of a contemporary custom carbon fiber AFO on gait effectiveness.15,16 The construction of the AFO allowed the user to lean into the pretibial shell so they could load the brace without concern of losing balance and falling forward. We sought to document the magnitude of load and, concomitantly, relate the mechanical characteristics of the AFO to walking function.
The participants showing the greatest increase in speed appeared to respond to and utilize the energy storing and releasing properties of the carbon-fiber composite AFO differently from the individuals who showed lesser increases in walking speed. This suggests that, among CMT patients, preferences for an increase in walking speed combined with the extent of muscle weakness may make certain mechanical properties of an AFO more desirable than others.
It is important to address the biomechanical needs of a CMT patient, since there may be bilateral strength differences due to progression of the disease. Optimizing the mechanical (energy storage and return) characteristics of the AFO to patient needs can be challenging. Until understanding of these relationships can be improved, one strategy may be to design AFOs of varying stiffness and allow patients to experience a range energy storage and release characteristics prior to selecting the stiffness they prefer. Alternatively, further research and development efforts may make it possible to conceive a design which allows the stiffness to be varied.