Comparison of silicone and posterior leaf spring ankle-foot orthoses in a subject with Charcot-Marie-Tooth disorder

Charcot-Marie-Tooth (CMT) is a hereditary motor and sensory neuropathy that generally results in bilateral lower limb weakness distal to the knees. In many cases weakness of the ankle musculature results in the need for orthotic treatment. The silicone ankle-foot orthosis (SAFO) was developed as an alternative form of orthotic management for persons with CMT. Few previous studies have attempted to quantify the effect of orthoses on ambulation in persons with CMT or compared the SAFO with other ankle-foot orthoses (AFOs). Hence, the purpose of this case study was to compare the function of SAFOs with thermoplastic posterior leaf spring AFOs (PLS-AFOs) in a subject with CMT type IX. Bilateral kinematic and kinetic data were acquired from a 49-year-old man instructed to ambulate at his normal self-selected speed over level ground with shoes alone (0.78 ± 0.05 m/s), bilateral SAFOs (0.93 ± 0.03 m/s), and bilateral PLS-AFOs (1.09 ± 0.03 m/s) using a marker-based motion capture system. Overall, the results of this study indicated that both AFO designs improved gait compared with the shoes-alone condition, but that the greatest degree of improvement occurred with the PLS-AFOs despite greater restriction in ankle range of motion [mean right/left (R/L): PLS-AFO 16.3°/20.4°; SAFO 22.2°/27.4°; control 29.1°]. The PLS-AFOs were able to correct gait deviations in both stance and swing phases, whereas the SAFOs affected predominantly swing phase ankle kinematics. The PLS-AFOs were able to increase the peak internal dorsiflexion moment during loading response, whereas the SAFOs had almost no effect during this period (mean R/L: -0.003/0.001; PLS-AFO -0.243/-0.253; SAFO -0.002/-0.003; control -0.06 Nm/kg). Although the SAFOs provided some toe clearance during swing phase by increasing mid-swing dorsiflexion when compared with the shoe-only condition, they did not do so to the same extent as the PLS-AFOs (mean R/L: shoe only -4.9°/-4.2°; PLS-AFO 5.8°/5.8°; SAFO -1.7°/0.5°). It was noted that both orthoses produced the same magnitude of knee hyperextension in late stance (mean R/L: PLS-AFO -7.2°/-5.9°; SAFO -7.1°/-6.6°). Perhaps limiting tibial progression transfers forward momentum to the thigh, which the weakened gastrocnemius is unable to restrain. Results of this study suggest that clinicians should not expect the SAFO to perform in the same manner as a thermoplastic PLS-AFO during level over-ground walking and that use of the SAFO would seem most appropriate for persons with gait deviations that are limited to mild equinus during swing phase.