Charcot-Marie-Tooth: AFO mechanics and gait patterns

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, Lower Extremity Review February 2014

Charcot-Marie-Tooth (CMT) disease affects an estimated one in 2500 individuals in the US. 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.

Matthew Downing puts an orthopedic brace on the foot of his son Matthew, 5. Both have Charcot-Marie-Tooth, a progressive neurodegenerative disorder. Michael Nagle for The New York Times . Listen to all the voices of CMT

Matthew Downing puts an orthopedic brace on the foot of his son Matthew, 5. Both have Charcot-Marie-Tooth, a progressive neurodegenerative disorder. Michael Nagle for The New York Times . Listen to all the voices of CMT.

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. 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. 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. 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.

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.
Janet S. Dufek PhD FACSM is associate professor and CoRE (collaborative research and education) Fellow at the University of Nevada, Las Vegas (UNLV), and co-director of the Biomechanics Laboratory. Edward S. Neumann PhD PE CP FAAOP is Professor Emeritus in the Department of Civil and Environmental Engineering and Construction at UNLV. M. Cameron Hawkins PhD is a lecturer in the Department of Mechanical and Biomedical Engineering at Boise State University in Idaho. Brendan O’Toole PhD is a professor in the Department of Mechanical Engineering and director of the Mendenhall Innovation Program and the Center for Materials and Structures at UNLV.

Continue reading in Lower Extremity Review

Functional and dynamic response characteristics of a custom composite ankle foot orthosis for Charcot-Marie-Tooth patients, Dufek JS, Neumann ES, Hawkins MC, O’Toole B. Gait Posture. 2014;39(1):308-13. doi: 10.1016/j.gaitpost.2013.07.121. Epub 2013 Aug 3.

Also see
Benefits of Exercise for kids with CMT in Hereditary Neuropathy Foundation
The Voices of Charcot-Marie-Tooth in The New York Times

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