Do Ankle-Foot Orthoses Reduce Cavovarus Deformity in Individuals With Charcot-Marie-Tooth Disease?

BACKGROUND: The use of ankle-foot orthoses (AFOs) is a mainstay in the treatment of cavovarus deformity associated with Charcot-Marie-Tooth (CMT) disease, but their ability to reduce cavovarus deformity is poorly characterized. Similarly, associations between AFO design features and degree of deformity reduction are unknown. Weightbearing CT has been used to describe CMT disease-related cavovarus deformity through both two-dimensional (2D) radiographic measures and three-dimensional statistical shape modeling (SSM). However, neither method has been used to evaluate differences in foot posture between standing barefoot and wearing AFOs, nor to examine relationships between AFO footplate design and foot morphology. QUESTIONS/PURPOSES: (1) Do 2D radiographic measurements demonstrate a reduction in cavovarus position between standing barefoot and standing with AFOs? (2) Does SSM demonstrate a reduction in cavovarus position between standing barefoot and standing with AFOs? (3) Is there an association between AFO footplate design and degree of reduction in cavovarus position between standing barefoot and standing with AFOs? METHODS: This prospective study consisted of adults diagnosed with CMT disease who presented to clinic while wearing bilateral AFOs between December 2023 and April 2025. Individuals with prior surgical correction, comorbid neurologic disorders, or unbraceable rigid foot were excluded. This yielded 20 individuals (10 females, 10 males; mean ± SD age 49 ± 17 years). Bilateral weightbearing CT scans were collected with the patient standing barefoot and while wearing AFOs and shoes. 2D radiographic measures (in °) that have been previously reported in CMT disease, consisting of hindfoot alignment angle, talar tilt angle, axial and sagittal talocalcaneal angle, tibiocalcaneal angle, axial and sagittal Meary angle, calcaneal inclination angle, calcaneal-first metatarsal angle, and first-second intermetatarsal angle, were automatically calculated using mathematical axis definitions. Differences between conditions were analyzed with generalized linear mixed-effect models, and differences > 20% of the normal range were considered clinically meaningful. An SSM of the foot was generated and analyzed with principal component analysis to describe population variation through a series of linear modes. Each mode describes a single spectrum, such as low to high arch or planovalgus to cavovarus foot, and accounts for a portion of population variance. The position of each sample along a mode is given by the shape score, and differences in shape scores between groups were analyzed with generalized linear mixed-effect models. Mean percent differences between limbs > 25% were considered meaningful. Participants used self-selected AFOs, and these were categorized into three classes of foot plate design: flat, custom, and flat with a custom orthotic between the footplate and the foot. Differences in demographics and baseline morphology between the three footplate groups were analyzed. RESULTS: 2D radiographic measurements demonstrated a mean 3.8° increase in sagittal Meary angle and mean 3.3° decrease in calcaneal-first metatarsal angle in the AFO scans relative to barefoot, representing a more cavovarus foot in the AFO condition (p < 0.001). SSM analysis demonstrated a mean 27% increase in overall cavovarus position, mean 54% increase in plantarflexion, and mean 42% increase in midfoot elevation in the AFO, relative to the barefoot condition (p < 0.001). Custom footplate AFOs showed smaller changes in calcaneal-first metatarsal angle and shape score than the flat footplate or flat footplate with orthotic AFOs (p = 0.04). CONCLUSION: Both methods of analysis demonstrated an increase in the cavovarus position of the foot while wearing AFOs. This supports the ability of weightbearing CT to be used in analysis of deformity reduction in an AFO. Subanalysis by footplate type suggested that customized footplates had a lesser deformity-exacerbating impact on foot posture than orthotics or flat footplates. CLINICAL RELEVANCE: Demonstrated functional benefits of AFO use in CMT disease may be attributed more to stabilization than deformity correction. Weightbearing CT analysis can demonstrate differences in foot posture within a limb with use of an AFO and may be a beneficial tool in future analysis of the effect of AFO design on foot structure.