Abstract Purpose Lower extremity coronal alignment parameters include varus, neutral, and valgus alignment as well as knee and ankle joint line obliquity (KJLO and AJLO). KJLO and AJLO are influenced by the intermalleolar distance during long‐leg standing radiographs (LSRs). This study quantifies the impact of intermalleolar distance on KJLO and AJLO during LSRs and evaluates whether it varies with osteoarthritis severity. Methods Radiologic analysis was conducted on 134 extremities. LSRs were obtained with the malleoli in contact and the feet placed shoulder‐width apart. Two blinded observers assessed the KJLO, AJLO and other lower extremity alignment parameters in two LSRs positions (open and closed). The coronal plane alignment of the knee (CPAK) and Hirschmann classifications were determined. Patients were categorised into three groups based on osteoarthritis severity: nonarthritic, early‐stage osteoarthritis, and advanced‐stage osteoarthritis. Differences between the osteoarthritis severity groups were analysed using analysis of variance. Based on the power analysis, the minimum required sample size was determined to be 42 extremities per group. Results The mean delta intermalleolar distance between the closed and open was 13.6 ± 4.8 cm with no significant difference across the osteoarthritis severity groups. Both KJLO and AJLO differed significantly different between the open and closed images ( p < 0.001), with the medial apex shifting proximally in the closed position ( p < 0.001). Linear regression showed that each 1 cm reduction in the intermalleolar distance resulted in 0.39° deviation in the KJLO ( p < 0.001), and 0.35° deviation in the AJLO ( p = 0.01). No significant differences in delta values were observed across osteoarthritis groups ( p > 0.05 for all). CPAK and Hirschmann classifications exhibited major subtype shifts in 6% and 25% of cases, respectively, but these differences were not statistically significant (CPAK: p = 0.69, Hirschmann: p = 0.070). Conclusion Knee and ankle joint obliquity are influenced by intermalleolar distance, independent of osteoarthritis severity. In LSRs imaging, standardising intermalleolar distance is crucial. Clinicians should account for deviations of 0.39° in KJLO and 0.35° in AJLO per centimetre of malleolar distance difference to ensure accurate measurements. Level of Evidence Level II, prospective cohort study.