BACKGROUND: The cause of hallux rigidus remains controversial. However, it is assumed that dysfunction of the windlass mechanism and metatarsus primus elevatus play a role in the pathology. Three-dimensional (3D) computed tomography (CT) imaging is ideal for analysis of movements of the foot, which involve 3D and rotational motion. The purpose of the present study was to compare the windlass mechanism in healthy normal feet with that in feet with hallux rigidus by 3D CT imaging. METHODS: A total of 17 feet with hallux rigidus and 21 normal feet were selected. Hallux rigidus was classified as grade 1 or 2 with use of the Coughlin and Shurnas system. CT imaging was performed during weight-bearing and non-weight-bearing with the first metatarsophalangeal joint in a neutral position or in 30° of dorsiflexion. We measured the rotation of each joint and the height of the navicular during dorsiflexion and weight-bearing. We also compared changes in the tarsometatarsal joint and metatarsus primus elevatus in the neutral position between the non-weight-bearing and weight-bearing conditions. RESULTS: During dorsiflexion, there were significant differences between the 2 groups in eversion and adduction at the talonavicular and talocalcaneal joints (p <
0.05), with less movement of bones in the hallux rigidus group. There was a significantly greater increase in height of the navicular in the control group than in the hallux rigidus group (1.2 ± 0.6 mm versus 0.7 ± 0.6 mm
p = 0.02). There was also a significant difference in metatarsus primus elevatus during the non-weight-bearing and weight-bearing conditions (p <
0.01). CONCLUSIONS: Hallux rigidus restricts the movement of the Chopart joint and hindfoot associated with dorsiflexion of the first metatarsophalangeal joint, suggesting an association between hallux rigidus and windlass mechanism dysfunction. LEVEL OF EVIDENCE: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.