Analysis of Sagittal Balance of the Spine During Various Standing Positions and Gait

Differences in the Sagittal Vertical Axis (SVA) during relaxed standing and walking to SVA during positions commonly assumed during x-ray acquisition has not previously been examined. Mean SVA values during three standing positions with varying shoulder and knee flexion were compared to the mean SVA during relaxed standing and gait. The mean SVA during relaxed standing (shoulders at 0° and knees at 0°) were positive, indicating forward positioning of the C7 vertebrae over the posterior aspect of the sacral endplate. Positions that involved 45° flexion of the shoulders exhibited a negative SVA, and were significantly different from relaxed standing as well as the mean SVA during gait (p=0.00). Forward flexion of the shoulders during x-ray acquisition allows for visualization of the spine, but changes the SVA to an abnormally negative position (approximately 5 cm posterior shift).