What is the best lateral radiograph positioning technique for assessment of sagittal balance: A biomechanical study on influence of different arm positions

Purpose: To evaluate the influence of different arm postures from the physiological standing position using force plate analysis of the gravity line. Methods: Forty healthy volunteered university students were enrolled. Each subject assumed different standing positions including standing with arms resting on the side (control), with fist over the clavicle (clavicular position), with active shoulder flexion in 30°, 60° and 90° with elbows extended (active flexion A), with hand rest on a bar with a static support (passive flexion P), and with hand rest on a bar with a drip stand (passive flexion D). The offset of the gravity line from the heel was measured by force plate analysis. The offset of the gravity line in different arm positions was compared with the control using paired t-test. Results: The mean anterior offset of the gravity line in control position is 39.80% of the foot length. All testing positions showed anterior shift of the gravity line compared with the control position from 0.51% to 7.50%. There were statistically significant changes of the gravity line from the control position in all (p < 0.05), except in the clavicular position (p = 0.249). Conclusion: All testing positions cause anterior shifting of the center of gravity from the physiological standing position. Clavicular position is the best comparable posture to the physiological standing position in taking a lateral radiograph. We recommend using the clavicular position as the standard testing position in the assessment of the sagittal profile.