Association Between Hindfoot Alignment and First Metatarsal Rotation

Abstract

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<.001) and Kim angles (0.615, p<.001). Hindfoot valgus was associated with 1st metatarsal pronation and hindfoot varus was associated with 1st metatarsal supination. There was a significant inverse relationship between Meary's angle and the Saltzman (r=-.600, p<.001) and Kim Angles (r=-.529, p<.001). This suggests that as Meary's angle decreases, as seen in a pes planovalgus deformity, 1st metatarsal pronation increases. Conclusion: There is significant correlation between hindfoot alignment and 1st metatarsal rotation. We demonstrated an association between hindfoot valgus and 1st metatarsal pronation, as well as between decreased Meary's angle and 1st metatarsal pronation. This suggests that 1st metatarsal pronation is associated with pes planovalgus deformity. We also report an association between hindfoot varus and 1st metatarsal supination, as well as between increased Meary's angle and 1st metatarsal supination. This suggests that 1st metatarsal supination is associated with cavovarus deformity. A derotational osteotomy/fusion may be required for first metatarsal rotational correction, in addition to hindfoot correction, for patients with cavovarus/planovalgus deformities.