Multiplanar Interactions in Cavovarus Foot Deformity

Research Type: Level 3 - Retrospective cohort study, Case-control study, Meta-analysis of Level 3 studies Introduction/Purpose: Charcot-Marie-Tooth (CMT) disease is the most common cause of neurogenic cavus foot. Prior weight bearing CT (WBCT) analysis has sought to understand 2D/3D morphologic differences between CMT and idiopathic pes cavus. WBCT better captures midfoot coronal and axial plane rotational deformity. The transverse tarsal arch is critical to foot stiffness, coupled with the medial longitudinal arch. Prior flatfoot studies have established that uncoupling of the transverse and medial longitudinal arch is more prominent compared to healthy controls. The objective was to determine if key differences in morphology, as assessed on WBCT, exist between pes cavus in individuals with CMT, idiopathic cavus, and healthy controls. Methods: This a single site IRB approved study including evaluation of WBCT images. Individuals between the ages of 18-65 years old with no prior foot and ankle surgery who were able to stand unassisted for WBCT were included. Groups were based on disease state (CMT cavus, idiopathic cavus, healthy controls). All patients with CMT had clinical or genetic confirmation. Medial column height was evaluated first using 2D measures. This was complemented by forefoot adduction/midfoot supination and a novel 3D measure of the transverse tarsal arch. Statistical analysis was performed using generalized linear models for repeated measures and pairwise comparisons between groups or Wilcoxon Rank Sum tests. P-values were adjusted for multiple comparisons using the stepdown Bonferroni method. Results: A total of 120 WBCT scans (n=40 CMT cavus, n=40 idiopathic cavus, n= 40 healthy controls) from 73 participants were analyzed. Six measurements evaluating medial column height were assessed: Meary’s angle, calcaneal pitch, cuneiform to floor and skin distances, as well as navicular to skin and floor distances. Forefoot adduction/midfoot supination was evaluated (axial talar-first metatarsal angle and forefoot arch angle). The transverse tarsal arch was assessed using a novel measure previously described to assess the transverse arch plantar (TAP) angle. All measures of the medial longitudinal height were greater in CMT vs controls (Table 1). Forefoot adduction was 3x greater in CMT cavus compared to controls. The TAP angle differed significantly between CMT (94.2 +/-13.4), idiopathic (100.5±9.4; p=0.02) and controls (102.7±7.8; p< 0.001). Conclusion: Forefoot adduction and midfoot supination are more pronounced in CMT pes cavus, likely due to the severity of muscular imbalances that characterize the progression of CMT. In addition, the transverse and medial longitudinal arch are more severely affected in CMT associated pes cavus. Prior flatfoot studies have identified the location of most substantial collapse as being between the plantar medial cuneiform and 2nd/3rd metatarsals. Our results demonstrate the exact opposite is true in CMT associated cavus, likely explaining the inherent stiffness in this foot morphology.