Association Between Hindfoot Alignment and First Metatarsal Rotation

Category: Other; Hindfoot; Midfoot/Forefoot Introduction/Purpose: The interplay between forefoot and hindfoot alignment has been well established in the literature for pathologies such as the flexible cavovarus foot. However, no study has evaluated the relationship between hindfoot alignment and first metatarsal axial rotation. Therefore, the purpose of this study is to determine the relationship, if any, between hindfoot alignment and first metatarsal axial rotation in patients with mild, moderate, and severe hindfoot varus/valgus deformity using weight bearing computed tomography (WBCT). We hypothesize that patients with hindfoot valgus alignment will be associated with a first metatarsal pronation/eversion deformity. Conversely, we hypothesize that patients with hindfoot varus alignment will be associated with a first metatarsal supination/inverted deformity. Methods: Patients who underwent weight bearing radiographs (WBR) and WBCT between 2015 and 2018 were evaluated with inclusion/exclusion criteria. Patients with prior foot surgery/trauma were excluded. Hindfoot alignment was evaluated using the calcaneal moment arm (Figure 1; horizontal distance between the most inferior aspect of the calcaneus and an extended line approximating the longitudinal axis of the tibia). Six subgroups were created based on the severity of hindfoot malalignment 1) Moderate valgus, 2) moderate varus, 3) substantial valgus, 4) substantial varus, 5) severe valgus, and 6) severe varus. Moderate was 1/2-1 standard deviations (SD) from the mean. Substantial was 1-2 SDs from the mean. Severe was >2 SDs from the mean. Patients with CMA values within ½ SD of the mean were excluded to focus on patients with significant hindfoot malalignment. First metatarsal axial rotation was measured using the Kim and Saltzman angles (Figure 1). Meary's angle was obtained using WBR. Results: 196 patients were included (average age - 52.6 years). The average CMA was +6.0+-16.2mm (valgus). The average Kim and Saltzman angles were 7.7+-12.9 and 2.8+-13.1 degrees (pronated). The average Meary's angle was 182.0+-11.9 degrees (>180 degrees-apex dorsal measurement). There was a significant association between hindfoot alignment and the Saltzman (r=0.641, p