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

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 positions. Therefore, this study aimed to investigate factors that can predict discrepancies in the coronal alignment of the lower limb between radiographs taken in the standing and supine positions. We retrospectively evaluated the medical records of patients who underwent full-length anteroposterior radiographs of the lower limb in both standing and supine positions between January 2019 and September 2021. 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, which is presented as the ΔHKA angle. Correlation and regression analyses were performed to analyse the relationship among ΔHKA angle, demographic data, and several radiographic parameters. In total, 147 limbs (94 patients) were included in this study. The mean ΔHKA angle was 1.3 ± 1.1° (range, 0-6.5°). The ΔHKA angle was significantly correlated with 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 the 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. Body mass index and advanced osteoarthritis affected the discrepancy in the coronal alignment of the lower limb between 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.