First Metatarsal Pronation Stratified by Tibial Sesamoid Position on Coronal Plane: A Study Based on Weight-Bearing Computed Tomography

Abstract Backgrounds: Few studies analyzed the coronal rotation of first metatarsal in hallux valgus patients with weightbearing computed tomography (WBCT). The purpose of this study is to investigate the association between hallux valgus parameters and first metatarsal head rotation in the coronal plane.Methods: Retrospective review of full standing WBCT scans were taken by PedCAT. A group of 123 patients with 216 feet, that intermetatarsal angle (IMA) >9 degrees and hallux valgus angle (HVA) >15 degrees, were included. 27 feet of 17 female included in control group. Measurements of forefoot hallux valgus parameters included IMA, HVA, distal metatarsal abduction angle (DMAA), metatarsal adduction angle (MAA), first metatarsal coronal rotation angle (α-angle), tibial sesamoid position (TSP) on dorsoplantar view, and sesamoid grading in the coronal plane. The differences of HVA, IMA, MAA, DMAA and α-angle in control and study group were compared by Wilcoxon rank test and student t test. Spearman correlation test was performed between α-angle and other parameters. General linear regression analysis was used to predict relationship parameters and α-angle.Results: The mean α-angle in the control group was 11.33±6.16 (range ,0-20) degrees, with the 95% confidence interval (CI) for the mean from 8.90 degrees to 13.77 degrees. The mean of α-angle in the study group was 23.75±6.32 (range,9-39) degrees, with the 95% CI from 22.90 degrees to 24.59 degrees. In the hallux valgus group, there were positive correlations between α-angle and IMA (Spearman’s correlation coefficient (rs) 0.137, P=0.044), DMAA (rs=0.176, P=.010) and TSP (rs=0.218, P=0.001). General linear regression analysis showed that α-angle was correlated with TSP (P<0.001). 208 hallux valgus feet (96.3%) had more pronation than the control group, whereas 8 feet (3.7%) had no or less pronation. Comparing the control and study subjects with the same TSP, means of α-angle showed significant difference, P=0.005.Conclusion: A large portion of hallux valgus patients had the first metatarsal pronation, which was positive correlated to TSP, IMA, and DMAA, and did not correlated to HVA and Smith grading. TSP is a useful predicting factor to α-angle changing. Level of Evidence: Level Ⅲ，Retrospective Cohort study