3D Analysis of Metatarsal Torsion by Computed Tomography in Normal, Hallux Valgus, and Hallux Rigidus Feet.

Background: One factor contributing to rotational deformity of the first metatarsal in hallux valgus is torsion of the metatarsal itself. Hallux rigidus also involves reduction of the longitudinal arch, but metatarsal torsion has not been discussed. We hypothesized that metatarsal torsion may be a morphologic change unique to hallux valgus. We compared 3-dimensional (3D) torsion of the first to fifth metatarsals between feet with hallux valgus, feet with hallux rigidus, and healthy control feet to investigate differences in the effects on pathologic conditions.

Methods: Participants were women of East Asian descent. There were 16, 16, and 14 feet in the control, hallux valgus, and hallux rigidus groups, respectively. One randomly selected control foot was designated as the reference foot. For comparison, nonweightbearing computed tomography images of the metatarsals were reconstructed in 3D, and the proximal and distal areas were superimposed on the reference foot. Torsion angle was defined as the rotational angle of the distal part of the articular axis relative to the proximal area. In the hallux valgus group, correlations of torsion angle with hallux valgus angle and intermetatarsal angle were calculated.

Results: The hallux valgus group had greater average pronation torsion in the first metatarsal than the control group and hallux rigidus group (11 and 13 degrees greater, respectively, P < .01). No significant differences were observed for the second to fifth metatarsals (P > .05). There was no significant correlation with hallux valgus angle or first-second intermetatarsal angle in the hallux valgus group (P > .05).

Conclusion: Hallux valgus feet had pronation deformities in the first metatarsals not observed in control or hallux rigidus feet, meaning that torsion toward pronation (eversion) in the first metatarsal was unique to hallux valgus. Improved surgical correction to diminish pronation may be necessary in patients with hallux valgus patients because of first metatarsal pronation in the first tarsometatarsal to normalize mechanical first-ray alignment.Level of Evidence: Level III, case-control stud.