First Ray Mobility in Hallux Rigidus, Hallux Valgus, and Normal Feet Based on Weightbearing Computed Tomography and Three-Dimensional Analysis

Abstract

Category: Midfoot/Forefoot; Bunion Introduction/Purpose: Both hallux rigidus (HR) and hallux valgus (HV) are conditions that occur in the first ray. Although both are believed to originate from hypermobility of the first ray, they each ultimately result in different clinical feature. Hypermobility of the first ray is strongly involved in the pathogenesis of HV. In contrast, several studies have reported an association between HR and hypermobility of the first ray but few have actually analyzed the nature of that association. We hypothesized that in HR, there would be little rotational movement despite the presence of hypermobility of the first ray. The purpose of this study was to evaluate the first ray mobility in feet with HR, HV, and in healthy feet by using weightbearing and non-weightbearing CT and 3D analysis. Methods: In this case-control study, we examined 17 feet of 11 healthy volunteers with no history of foot disorders and no symptoms such as pain in the foot (control group), 16 feet of 16 patients with HV and 16 feet of 11 patients with HR. First, non- weightbearing foot CT imaging was performed with the participant supine on our original loading device, with the legs extended and the ankle in a neutral position, and then weightbearing CT imaging was performed by applying a load equivalent to body weight. Using an iterative closest point algorithm, each joint in the first ray—the talonavicular joint, the medial cuneonavicular joint, and the first tarsometatarsal (TMT) joint—was aligned using its respective proximal bone. Displacement of the distal bone relative to the proximal bone was quantified in 3D under both weightbearing and non-weightbearing conditions. Results: In the talonavicular joint, the HV group showed significantly greater eversion (p = 0.011) than the control group, and greater dorsiflexion (p = 0.027) and eversion (p < 0.01) than the HR group. In the medial cuneiform joint, the HV group showed significantly greater eversion (p < 0.01) and abduction (p = 0.011) than the control group. In the first TMTl joint, the HV group showed significantly greater dorsiflexion (p = 0.014), inversion (p = 0.028), and adduction (p < 0.01) than the control group, and greater inversion (p < 0.01) and adduction (p < 0.01) than the HR group. The HR group showed significantly greater dorsiflexion (p = 0.026) than the control group. Conclusion: In the present study, hypermobility was observed at the first TMT in both HV and HR. However, the changes in HR were mainly in the sagittal plane, whereas those in HV were in all three planes. This difference may explain the different clinical feature ultimately observed in each condition. Future studies involving comparison of various severity levels and postoperative analysis should elucidate the pathophysiology and contribute to selection of appropriate treatment as well as the development of new treatments for HV and HR.