Automated 3-Dimensional Measurements of First Metatarsal Dysplasia in Hallux Valgus

Pronation of first metatarsal (M1) in hallux valgus (HV) is currently the subject of a growing body of scientific research. Several methods of manual measurements have been developed, providing heterogeneous results. Our objective was to develop automatic 3D weightbearing computed tomography (WBCT) measurements in a retrospective case-control design to compare coronal rotation of M1 head relative to the ground, M1 intrinsic torsion, and valgus deviation of M1 distal articular surface (or distal metatarsal articular angle [DMAA]) in HV and controls.

Forty-four symptomatic HV and 44 matched controls were retrospectively enrolled, all of whom had undergone WBCT acquisition. Bone segmentation was performed (Bonelogic 2.1 software). Two methods were developed to assess position of the M1 head. One was based on automatic geometric fitting of a cylinder on the head, and the other on automatic selection of the position of the sesamoid gutters. Similarly, 2 methods were developed to assess the position of the M1 base. One was defined using principal components analysis (PCA) of the proximal articular surface of M1, and the other using the longest diagonal of the M1 base.

First metatarsal head rotation relative to the ground was, respectively, 8.9° ± 8.4° (95% CI 6.1°-11.7°) and 2.1° ± 6.4° (95% CI 0.1°-4.1°) via the cylinder method (P < .001) and 9° ± 8.3° (95% CI 6.2°-11.8°) and 0.7° ± 6.8° (95% CI -1.4° to 2.8°) via the gutters method (P < .001) in the 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°. The DMAA was 11.4° ± 6.9° (95% CI 9.3°-13.5°) in the HV group and 5.6° ± 4.7° (95% CI 4.1°-7.0°) in the control group (P < .001).

Using automatic 3D WBCT measurements, we found that HV showed an increase in M1 head pronation relative to the ground of 7° to 8° greater than controls, with an increase in M1 intrinsic torsion in pronation of 2° to 5° and an increase in valgus deviation of the M1 distal articular surface of approximately 6°. Changing measurements reference points altered angular values in our study, particularly when moving from measurements based on the sesamoid gutters to gutter-independent measurements, highlighting that these methods may capture different anatomic constructs.

Level III, case control study.