Which Lateral Radiographic Positioning Technique Provides the Most Reliable and Functional Representation of a Patient’s Sagittal Balance?

Abstract

Prospective nonscoliotic cohort evaluation of the effects of various positions for obtaining standing lateral thoracolumbar radiographs. The purpose of this study was to compare the effects of various upper extremity positions on thoracolumbar sagittal spinal alignment. The standing position used to capture a lateral plane radiograph can have marked effects on measurements of sagittal spinal alignment and may compound the variability between measurements from successive radiographs. Twenty-two healthy female adolescents performed 3 repeated trials of 4 standing positions in a motion analysis laboratory. The positions included: (1) relaxed standing with arms at sides (CONTROL), (2) standing with fists overlying ipsilateral clavicles (CLAVICLE), (3) active shoulder flexion to 30 degrees with elbows extended (30 ACTIVE), and (4) passive shoulder flexion to 30 degrees with hand supports (30 PASSIVE). Sagittal alignment of the spine was described by kyphosis, lordosis, and the sagittal vertical axis (SVA), all of which were measured from the positions of reflective markers attached to the surface of the back and pelvis. Differences between alignment measures obtained for each of the 3 radiographic positions relative to the functional position (CONTROL) were calculated. Mean differences were then compared between positions using repeated measures ANOVAs (alpha = 0.05). Relative to the CONTROL position, all other positions resulted in negative shifts in SVA (range = -1.1 cm- -4.6 cm), decreased kyphosis (range = -1 degrees- -3 degrees), and increased lordosis (4 degrees for all positions). The shift in the SVA with the 30 PASSIVE position was significantly less than the other 2 positions (P < 0.05) and demonstrated the least variability. Standing with the hands supported while flexing the shoulders 30 degrees during positioning for lateral spinopelvic radiographic acquisition resulted in an SVA and measures of sagittal plane curvature that were comparable with a functional standing position with arms at the side. This seems to be the best way to move the arms anterior to the spine with the least effect on overall sagittal balance.