Automated Three-Dimensional Measurements of First Metatarsal Dysplasia in Hallux Valgus

Research Type: Level 3 - Retrospective cohort study, Case-control study, Meta-analysis of Level 3 studies Introduction/Purpose: The pronation of the first metatarsal (M1) in hallux valgus (HV) is currently the subject of a growing body of scientific research. Several methods of manual measurement have been developed, providing heterogeneous results. Our objective was to develop automatic 3D WBCT measurements to compare coronal rotation of M1 head relative to the ground, M1 intrinsic torsion and valgus deviation of M1 distal articular surface (DMAA) in HV and controls. Methods: Forty-four symptomatic HV and 44 matched controls were retrospectively enrolled in this study, all of whom had undergone WBCT acquisition. Bone segmentation was performed (Bonelogic 2.1® software). Two methods were developed to assess position of M1 head. One was based on automatic geometric primitive fitting of a cylinder on the head, and the other on automatic selection of the position of the sesamoid gutters. Similarly, two methods were developed to assess the position of the M1 base. One was defined using principal component analysis (PCA) of the proximal articular surface of M1, and the other using the longest diagonal of the M1 base. Results: First metatarsal head rotation relative to the ground was respectively 8.9±8.4 degrees and 2.1±6.4 degrees (cylinder method, p< 0.001), and 9±8.3 degrees and 0.7±6.8 degrees (gutters method, p< 0.001) in HV and control groups. Combining the different sets of head and base measurements, the increase in M1 intrinsic torsion in HV ranged from 2 to 5 degrees. The DMAA was 11.4±6.9 degrees in the HV group and 5.6±4.7 degrees in the control group (p < 0.001). Conclusion: Using automatic 3D WBCT measurements we found that HV showed an increase in M1 head pronation relative to the ground of 7 to 8 degrees greater than controls, with an increase in M1 intrinsic torsion in pronation of 2 to 5 degrees and an increase in valgus deviation of the M1 distal articular surface of approximately 6 degrees. Changing measurements reference points altered angular values in our study, particularly when moving from measurements based on the sesamoid gutters to gutter-independent measurements, suggesting that the cylinder method may be more reliable. Figure 1 to 5 and Table 2 and 3.