Factor affecting the discrepancy in the coronal alignment of the lower limb between the standing and supine radiographs

Background: Conflicting results have been reported regarding the factors that can predict the discrepancy in the coronal alignment of the lower limb between radiographs taken in the standing and supine status, and even few studies have been conducted on this issue. The purpose of this study was to investigate factors that can predict the discrepancies in the coronal alignment of the lower limb between radiographs taken in the standing and supine status. Methods: : Between January 2019 to September 2021, medical records of patients who took full-length anteroposterior radiographs of the lower limb in both the standing and supine status were retrospectively evaluated. The discrepancy in the coronal alignment of the lower limb between the standing and supine radiographs was defined as the absolute value of the difference in the Hip-Knee-Ankle (HKA) angle between the two radiographs, presented as ΔHKA angle. Correlation and regression analyses were performed to analyze the relationship between the ΔHKA angle and the demographic data and several radiographic parameters. Results: : A total of 147 limbs (94 patients) were included in this study. The mean ΔHKA angle was 1.3 ± 1.1° (range, 0° to 6.5°). The ΔHKA angle was significantly correlated with the body mass index and several radiographic parameters, including the HKA angle, joint line convergence angle, and osteoarthritis grade. Subsequent multiple linear regression analysis was performed using the radiographic parameters measured on the supine radiographs with the two separate models from two observers, which revealed that body mass index and advanced osteoarthritis (Kellgren-Lawrence grades 3 and 4) had a positive correlation with the ΔHKA angle. Conclusions: : Body mass index and advanced osteoarthritis affected the discrepancy in the coronal alignment of the lower limb between the standing and supine radiographs. A discrepancy in the coronal alignment of the lower limb could be more prominent in patients with an increased body mass index and advanced osteoarthritis corresponding to Kellgren-Lawrence grades 3 and 4.