First ray mobility in hallux rigidus, hallux valgus, and normal feet based on weightbearing computed tomography and three-dimensional analysis: A case-control study.

ABSTRACT

BACKGROUND: Hallux valgus and hallux rigidus are disorders affecting the first ray and are associated with hypermobility of this structure. This study aimed to investigate the three-dimensional mobility of each joint of the first ray between feet with hallux valgus or hallux rigidus and healthy feet using weightbearing and nonweightbearing computed tomography (CT). METHODS: This case-control study analyzed 17 feet of 11 healthy volunteers (control group), 16 feet of 16 patients with hallux valgus (HV group), and 16 feet of 11 patients with hallux rigidus (HR group). First, nonweightbearing foot CT imaging was performed in the supine position on a loading device with no load applied, with the legs extended and the ankle in the neutral position. Next, a load equivalent to body weight was applied for weightbearing CT imaging. Distal bone displacement relative to the proximal bone was quantified three-dimensionally under both conditions. RESULTS: In the HV group, the talonavicular joint showed significantly greater eversion (P = 00.011) compared with the control group and significantly greater dorsiflexion (P = 00.027) and eversion (P < 00.01) compared with the HR group. In the medial cuneiform joint, the HV group showed significantly greater eversion (P < 00.01) and abduction (P = 00.011) than the control group. For the first tarsometatarsal joint, the HV group showed significantly greater dorsiflexion (P = 00.014), inversion (P = 00.028), and adduction (P < 00.01) than the control group, and greater inversion (P < 00.01) and adduction (P < 00.01) than the HR group. Dorsiflexion of the first tarsometatarsal joint was significantly greater in the HR group compared with the control group (P = 00.026). CONCLUSION: Hypermobility of the first ray appears to be three-dimensional in hallux valgus, it is centered at the first tarsometatarsal joint, while in hallux rigidus it is mainly in the sagittal plane at the first tarsometatarsal joint only. This difference may explain the different deformities ultimately observed in each condition.