Three Dimensional Weightbearing CT Assessment of Metatarsal Osteotomies for Hallux Valgus Correction

CATEGORY: Bunion; Midfoot/Forefoot INTRODUCTION/PURPOSE: Hallux valgus (HV) is a tri-plane deformity of the foot corresponding to a medial deviation of the first metatarsal and a lateral deviation of the hallux. Understanding key angles between bones, as well as how these deformity changes in each plane, is critical to generating pre-operative insights into the most effective surgical correction of the deformity. While two- dimenional (2D) imaging can provide some information; utilizing three-dimensional (3D) imaging can include more precise and accurate measures of hallux valgus. The purpose of this study is to evaluate the metatarsal osteotomies for correction of hallux valgus deformity in axial, coronal and sagittal plane with 2D and 3D measurements with the hypothesis that 3D measurements will provide greater accuracy of pre and post surgical changes METHODS: Ten cadaveric specimens were selected and weight-bearing CT scans were taken pre operatively with an applied an axial load of 80 pounds. Midshaft osteotomies were then performed on the cadaveric specimens followed by weight-bearing CT scans taken post-operatively.3D models of the pre-operative and post-operative specimens were created and differences in pre and post operative changes were analyzed using conventional 2D and 3D models of the first metatarsal (M1), second metatarsal (M2), fifth metatarsal (M5), and proximal phalanx of the hallux (PP1) using a paired student t-test. Quantitative examination of foot and ankle offset (FAO) alignment along with congruity of first metatarsal phalangeal and first tarsometatarsal joints RESULTS: 3D measurements of the Inter-Metatarsal (IM) Angle, was 12.3 degrees pre-opeative and 10.4 degrees post-operative with no significant differences in all three planes while the M1M5 Angle, measured between the principle axes of the first metatarsal and fifth metatarsal was 25.3 degrees pre-operative and 22.0 degrees post-operative were statistically significant with the greatest change in the axial plane. 2D measurements of the hallux valgus angle, measured the longitudineal axes of the first metatarsal and proximal phalange of the hallux was 22.6 degrees pre opereative and 21.7 degrees post opereative with no statistical difference while the metatarsal parabola, measured in two dimensions projected onto the axial plane was 157.1 degrees before and 141.5 degrees after surgery was statistical significant. CONCLUSION: When comparing 2D and 3D pre and post surgical hallux valgus values, the only significant differences were identified in the absolute M1M5 values in the axial plane and a significant change was also observed in the metatarsal parabola angle. While the metatarsal parabola angle are sensitive measures, these results suggest that the M1 M5 angle allows for precise, efficient measurements in axial, coronal and sagittal planes that is previously unknown through two-dimensional radiographic measurements for quantifying the effect of metatarsal osteotomies on hallux valgus