3-Dimensional Analysis of First Tarsometatarsal Joint after First Metatarsal Osteotomy with Weightbearing CT (WBCT)

CATEGORY: Midfoot/Forefoot; Bunion INTRODUCTION/PURPOSE: The pathology of the bunion deformity consists of deformities in the axial, coronal, and sagittal planes of the first metatarsal and its articular surface with the medial cuneiform. While weightbearing radiographs have been utilized for assessment of these deformities, such methods have limitations with regard to image magnification, patient position, and superimposition of bone alignments. With advances with weightbearing computed tomography (WBCT), evaluation of the 3- dimensional components of the first metatarsal along with its proximal articular surface can be assessed with greater precision. This study aims to observe the effect of the midshaft osteotomy on the alignment of the tarsometatarsal joint in three dimension METHODS: Ten feet in 10 subjects underwent midshaft first metatarsal osteotomies. Weight-bearing (using a load equivalent to body weight) CT scans with .3mm cubic voxel size using an original loading device preoperatively and postoperatively were collected from each of the subjects in neutral standing position. Scans were segmented, and 3D renderings of the medial cuneiform, first metatarsal, and the first phalanx were also generated from the segmentations followed by definition of reference frames to evaluate changes in the metatarsal in relationship to the medial cuneiform. (Fig.1) RESULTS: The measurements of the rotational parameters showed greater changes in the sagittal plane postoperatively with dorsiflexion of the first metatarsal relative to the medial cuneiform at the first tarsometatarsal joint (p<0.05).(Fig.2) Post-operative changes in the coronal plane and axial plane with relationship of the first metatarsal to the medial cuneiform were noted. Distance mapping showed a significant increase in surface-to-surface distance at the dorsal tarsometatarsal joint post-operatively with a reduced distance at the inferior portion of the tarsometatarsal joint. (Fig.3). CONCLUSION: Based on the results of the study, midshaft osteotomies of first metatarsal can cause increased dorsiflexion in the sagittal plane, significant eversion in the coronal plane, and external rotation in the axial plane at the tarsometatarsal joint. Distance mapping analysis on WBCT images identified differences in surface-to-surface interaction of the first metatarsal and the medial cuneiform