Assessing the effects of sway-back posture on global and regional spinal sagittal angles using inertial measurement units

BACKGROUND: Sway-back posture in the sagittal profile is a commonly adopted poor standing posture. Although the terms, definitions, and adverse health problems of sway-back posture are widely used clinically, few studies have quantified sway-back posture. OBJECTIVE: To investigate spinal sagittal alignment in sway-back posture while standing based on global and regional angles using inertial measurement units (IMUs). METHODS: This cross-sectional study recruited 30 asymptomatic young adults. After measuring the sway angle while standing, the participants were divided into sway-back and non-sway-back groups (normal thoracic group). Each participant stood in a comfortable posture for 5 seconds with IMUs at the T1, T7, T12, L3, and S2 levels. Then, we measured the global and regional lumbar and thoracic angles and sacral inclination in the standing position. RESULTS: Although there was no difference in the global lumbar angle, there was a difference in regional lumbar angles between the two groups. The normal thoracic group had balanced lumbar lordosis between the upper and lower lordotic arcs, whereas the sway back group tended to have a flat upper lumbar angle and increased lower lumbar angle. CONCLUSION: It is useful to assess the global and regional angles in the spinal sagittal assessment of individuals with sway-back posture.