Category: Hindfoot; Other Introduction/Purpose: The hindfoot deformity seen in Charcot-Marie-Tooth disease (CMT) is poorly understood, and the contribution of abnormal bone morphology has never been conclusively demonstrated. The purpose of this study was to compare the three-dimensional (3D) bone morphology of the talus, calcaneus and navicular in a cohort of CMT patients versus a control population. We used the data obtained from weight-bearing computed tomography (WBCT) to reconstruct the geometric shape of each bone using 3D surface meshing techniques. Surface mesh analysis of this type is commonly used in engineering to evaluate and optimize 3D geometries and structures. Methods: A total of 17 WBCTs from 15 patients (average age 24) with CMT who underwent WBCT without previous surgeries, degenerative changes or open physes were included. These were compared to 20 healthy control WBCTs. Calcaneal measurements included the radius of curvature and the angle between the posterior tuberosity and posterior facet in the sagittal plane. Talar measurements include axial and sagittal declination between the body and neck as well as coronal rotation of the talar head relative to the body. Surface-mesh model analysis was performed comparing the average of the CMT cohort to the controls using CT analysis software (Disior Bonelogic). Means were compared with a t test (p<0.05). Results: CMT patients had significantly less sagittal declination (plantarflexion) versus controls (14.9 versus 25.1 degrees respectively) (p<0.01). Similarly, CMT patients had less talar head coronal rotation versus controls (30.2 versus 42.5 degrees respectively) (p<0.001). There was no difference in axial rotation of the talar neck versus body between the groups (p=0.88). The calcaneal radius of curvature in CMT patients was significantly smaller than the control population (716.6 versus 2143.5 mm respectively) (p<0.05). Angular differences were also significant between the posterior tuberosity and posterior facet of the subtalar joint in the sagittal plane (CMT 57.7 degrees, control 67.9 degrees) (p<0.001). Additionally, surface-mesh model analysis demonstrated the largest differences in morphology at the navicular tuberosity, medial talar head, sustentaculum tali and anterior process of the calcaneus (Figure 1). Conclusion: This is the first study to quantify the morphologic differences in osteology seen in CMT patients. The decreased sagittal declination of the talar neck is seen with a reciprocal decreased slope of the posterior facet of the calcaneus. The coronal rotation of the talar head and abnormal navicular tuberosity morphology shows changes seen in patients with CMT and may be attributed to unbalanced pull of the posterior tibial tendon during development. These findings will help refine, and potentially revolutionize the surgical reconstruction of cavovarus deformity in CMT patients.