Hallux rigidus is a pathological condition affecting the great toe and, after hallux valgus, is the second most common foot disorder of the first metatarsophalangeal (MTP) joint [1,2]. Both hallux rigidus and hallux valgus 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 features. Extensive research using various methods, including plain radiographs, specially created devices, and computed tomography (CT), has demonstrated that hypermobility of the first ray is strongly involved in the pathogenesis of hallux valgus [[3], [4], [5]]. In contrast, an association between hallux rigidus and hypermobility of the first ray has been suggested [6] but only one study has actually analyzed the nature of that association [2]. In a previous study involving weightbearing CT and three-dimensional (3D) analysis, 3D hypermobility of the first ray, including rotational hypermobility, was observed in feet with hallux valgus [5]. We hypothesized that feet with hallux rigidus exhibit hypermobility of the first ray only in the sagittal plane, which is a different pathology of hallux valgus.

In the present study, we conducted a detailed 3D analysis comparing first ray mobility in feet with hallux rigidus, in feet with hallux valgus, and in healthy feet by using weightbearing and non-weightbearing CT imaging.