Functional and dynamic response characteristics of a custom composite ankle foot orthosis for Charcot-Marie-Tooth patients.

BACKGROUND: Custom carbon-fiber composite ankle foot orthoses (AFOs) have been anecdotally reported to improve gait of Charcot-Marie-Tooth (CMT) patients. The purpose of the study was to characterize the spatio-temporal, joint kinetic and mechanical responses of a custom carbon fiber AFO during locomotion for persons diagnosed with CMT.

METHODS: Eight volunteers were fitted with custom AFOs. Three of the devices were instrumented with eight strain gauges to measure surface deformation of the shell during dynamic function. Following a minimum 10 weeks accommodation period, plantar- and dorsiflexor strength was measured bilaterally. Volunteers then walked unbraced and braced, at their preferred pace over a force platform and instrumented walkway while being tracked with a 12-camera motion capture system. Strength, spatio-temporal and lower extremity joint kinetic parameters were evaluated between conditions (single subject) using the model statistic procedure. Mechanical loads were presented descriptively.

RESULTS: All participants walked faster (89.4 ± 13.3 vs 115.6 ± 18.0 cm/s) in the braced condition with ankle strength negatively correlated to speed increase. As Δ velocity increased, maximum joint moments during loading response shifted from the hip joint to the ankle and knee joints. During propulsion, the hip joint moment dominated. Subjects exhibiting the greatest and least Δ velocity imposed an average load of 54.6% and 16.6% of body weight on the braces, respectively. Energy storage in the brace averaged 9.6 ± 6.6J/kg.

CONCLUSION: Subject-specific effects of a custom AFO on gait for CMT patients were documented. The force-deflection properties of carbon-fiber composite braces may be important considerations in their design.