Static radiographic alignment fails to capture the dynamic nature of joint behaviour during functional tasks. To address this, our study evaluated the relationship between Hip-Knee-Ankle angle (HKAA) and dynamic biomechanical variables (dynamic HKAA (dHKAA), via projection of hip, knee, and ankle joint centers onto the frontal plane, knee adduction moment (KAM), and knee abduction angle (KAA)), during gait and sit-to-stand tasks with and without arm assistance. A further objective was to examine the mediolateral center of pressure (COP ML) as a complementary parameter for assessing joint loading and frontal plane alignment. Twenty-two patients (mean age 67 ± 9 years, BMI 28.7 ± 3.4 kg/m2) with end-stage knee osteoarthritis scheduled for total knee arthroplasty were recruited. HKAA was extracted from full-length standing radiographs, while dynamic variables from 3D motion capture and force plates data. Associations between static and dynamic parameters were evaluated using correlation and linear regression analyses. dHKAA consistently exhibited stronger correlations with KAM and KAA than radiographic HKAA, particularly during gait loading response (ρ = 0.93;​ R² = 0.84, p < 0.01). Similar trends were observed in the other tasks, where HKAA showed limited associations. COP ML showed moderate correlations with KAM but none with dHKAA. These findings suggest that HKAA alone may not reliably capture functional joint loading, and that dHKAA provides a more comprehensive assessment of frontal plane knee behaviour. COP ML showed limited associations and should be cautiously interpreted in this context. These findings may enhance clinical assessments, surgical planning, and advancing-personalized, biomechanically driven intervention research.