Frontal Plane Rotation of the First Ray in Hallux Valgus using Standing Computerized Tomography (CT)

Abstract

The purpose of the present study was to analyze the difference in frontal plane rotation of the entire first ray in patients with and without hallux valgus using standing weightbearing computed tomography (CT). Ten feet of 10 patients with hallux valgus and 36 feet of 36 patients without hallux valgus were examined. Standing weightbearing CT scans and radiographs were taken for all subjects. Frontal plane measurements of the sesamoid apparatus, first metatarsal head, first metatarsal base, and medial cuneiform were performed. Frontal plane rotation of the first tarsometatarsal joint and intrinsic first metatarsal torsion was calculated. An independent 2 sample t test was used to compare means of outcomes of interest across control and treatment groups. Statistical significance was set at an alpha level of 0.05. There was a significant increase in pronation of the sesamoid apparatus (23.49° vs 6.60°) and first metatarsal head (17.79° vs 9.81°) in patients with hallux valgus. There was a significant increase in first metatarsal torsion toward pronation in patients with hallux valgus (22.28° vs 13.52°). No significant difference was detected in the rotation at the first tarsometatarsal joint or the frontal plane orientations of the first metatarsal base and medial cuneiform. By examining the frontal plane position of the entire first ray during weightbearing using standing CT in patients with and without hallux valgus, we determined the level at which pronation originates to be within the first metatarsal bone rather than the first tarsometatarsal joint.

Keywords: bunion; foot CT; foot instability; forefoot; pronation; tri-plane deformity; weight bearing CT.