Three-Dimensional Assessment of Charcot Neuroarthropathy Deformities: Comparison of Standard 2D vs Patient-Specific 3D Measurements

Background: The purpose of this study is to compare foot and ankle deformity measurements obtained from 2-dimensional (2D) radiographs vs 3-dimensional (3D) modalities in Charcot neuroarthropathy (CN) feet by using a patient-specific coordinate system. Methods: This retrospective study reviewed foot and ankle imaging for 25 patients with a diagnosis of CN of the lower extremity, type 2 diabetes mellitus with diabetic neuropathy, or lower limb neuropathy. Radiographs and either computed tomography (CT) or magnetic resonance imaging (MRI) scans were obtained for each patient and used to make angle and distance measurements used clinically to describe deformity. 2D measurements were obtained using standard methods, involving annotating planar radiographs. The 3D measurement procedure began by manually placing fiducials on anatomic landmarks. Then, a custom-built code was used to automatically transform the foot into a patient-specific anatomic coordinate system and calculate all angle and distance measurements. Each scan was measured by 2 observers and intraclass correlation was calculated for each imaging type. Results: The average age of the patients was 61 years, with 92% being White and 88% having diabetic neuroarthropathy. Measurements for anteroposterior talocalcaneal angle and lateral column height were larger when measured on MRI (91.1 ± 16.7 degrees vs 29.1 ± 2.8 degrees, P = .004) and CT (78.6 ± 18.5 degrees vs 24.6 ± 2.7 degrees, P = .020) compared with radiographic measurements. Additionally, MRI demonstrated significantly greater interobserver reliability for the talocalcaneal angle (0.74 vs 0.19, 95% CI 0.11, 0.96), suggesting improved detection of hindfoot valgus compared with radiographs, whereas CT reliability was comparable to plain radiographs. Conclusion: Larger measurements and higher interobserver reliability for the talocalcaneal angle on 3D modalities suggest that a patient-specific 3D approach may improve detection of transverse-plane malalignment in Charcot neuroarthropathy.