The Longitudinal Axis of the Inter-Sesamoid Crista in Hallux Valgus and Its Relationship with the Distal Metatarsal Articular Angle. A Case Control Study

Abstract

Category: Bunion; Midfoot/Forefoot Introduction/Purpose: Little is known about the intersesamoid crista in Hallux Valgus (HV). However, this structure directly interfaces with the sesamoids and surrounding soft tissues and might play an important role in HV deformity. Our primary objective was to compare the angulation between the crista and first metatarsal (M1) longitudinal axis in HV and controls. Our secondary objective was to assess its correlation with the Distal Metatarsal Articular Angle (DMAA). We hypothesized that the longitudinal axis of the crista will be deviated in valgus in HV and that its position will be correlated with the DMAA. Methods: This IRB approved retrospective case control study evaluated 9 HV and 8 controls matched on age, BMI, and gender. The DMAA was measured as initially described on X-Rays, and then on weight-bearing CT images using a previously validated technique including pronation correction of the M1 called 3d-DMAA. To identify the angle of the inter-sesamoid crista relative to the shaft of the 1st metatarsal, CT scans were semi-automatically segmented to create 3D models of the forefoot. The crista was selected in Geomagic Design X and the resulting STL models were imported into MATLAB for analysis. Principal component analysis was used to identify the direction of both the crista and the 1st metatarsal shaft. The crista-shaft angle is the angle between the directions of greatest variation. Normality was assessed using Shapiro-Wilk tests. Comparisons were made using Student T-tests for normal variables and Mann-Whitney for non-normals. Correlations were assessed using Pearson's coefficients. Results: The crista deviated from the 1st metatarsal shaft in valgus in all the cases (HV and controls). There was a significant increase in valgus deviation of the crista in HV compared to controls (respectively 14.4+/-8.7 degrees and 5.5+/-3.2 degrees; p=0.017). Mean DMAA were respectively 25.1+/-7.9 degrees in HV and 7.4+/-2.9 in controls (p<0.001). Mean 3d-DMAA were respectively 12.5+/-5.6 degrees in HV and 3.1+/-2.4 in controls (p<0.001). There was a low positive non-significant correlation between the crista deviation and the DMAA (ρ=0.44; r2=0.193; p=0.078). There was a moderate positive significant correlation between Crista M1 Angle and 3D-DMAA (ρ=0.57; r2=0.326; p=0.017). Conclusion: The longitudinal axis of the inter-sesamoid crista deviates from the 1st metatarsal shaft in valgus in HV compared to controls. This follows the pattern of the 3d-DMAA which reflect the valgus deviation of the articular surface after exclusion of the pronation which is an important confounding factor of the original DMAA. The inter-sesamoid crista may play a role in HV pathophysiology as a possible lateral destabilizer of the surrounding soft tissues in HV. Surgically correcting the DMAA with a distal osteotomy might also correct the crista position in HV.