Pilot Study of a 3-Dimensional Method for Analysis of Pronation of the First Metatarsal of Hallux Valgus Patients

BACKGROUND:: The current work sought to quantify pronation of the first metatarsal relative to the second metatarsal and of the proximal phalanx of the great toe relative to the first metatarsal. METHODS:: Three-dimensional models were reconstructed from weightbearing computed tomography (CT) images (10 hallux valgus, 10 normal). The orientations of bones related to hallux valgus (HV) (ie, the phalanx, first and second metatarsals) were determined from coordinate systems established by selecting landmarks. After determining the hallux valgus and intermetatarsal angles, additional calculations geometrically determined the 3-dimensional (3D) angles using the aeronautical system of yaw-pitch-roll. The 3D geometrically determined angles were compared to the conventional plain radiographic angles. RESULTS:: HV measurements taken with CT and 3D computer-aided design (3DCAD) geometric methods were the same as measurements taken from plain radiographs (P > .05). The average pronation of the first metatarsal relative to the second metatarsal was 8.2 degrees greater in the hallux valgus group (27.3 degrees) than in the normal group (19.1 degrees) (P = .044). A regression analysis of pronation vs intermetatarsal angle (IMA) was not found to be significant. There was also no correlation between pronation of the great toe and first metatarsal in the HV group. CONCLUSIONS:: The pronation angle of the first metatarsal relative to the second metatarsal between normal and hallux valgus patients was larger in HV patients but was not well correlated with the IMA. CLINICAL RELEVANCE:: The findings of this study indicate that pronation may need to be considered in the operative correction of hallux valgus for restoration of normal anatomy.