The effect of pelvic motion on spinopelvic parameters

To date, many studies have examined how pelvic position affects the spinal curvature and spinopelvic parameters. However, these studies focus on a static relationship, comparing pelvis and spine in a relaxed or baseline position only. Indeed, the spinopelvic connection is dynamic, as subjects can easily be taught to rotate their pelvis anteriorly or posteriorly on the femoral head, all while maintaining an erect posture. Therefore, for a true understanding of pelvic influence on the spinal column, it is necessary to examine spinopelvic parameters in multiple pelvic positions within the same subject.The objective of this study was to examine the dynamic effect of pelvic motion on the spine and associated radiographic parameters.This is a single-center, cross-sectional study of 50 healthy, asymptomatic volunteers.Subjects were recruited and screened based on the following criteria: between 18 and 79 years of age; no known spinal, pelvic, or lower extremity pain lasting for >48 hours; no history of spinal, pelvic, or lower extremity dysfunction requiring medical care; no radiographic evidence of spinal or pelvic abnormality, scoliosis deformity, or other associated spinal pathologies; not currently pregnant and with no possibility of being pregnant; and a body mass index of <30. 64. The subjects were screened and 14 were excluded for a total of 50 subjects.The outcome measures included thoracic kyphosis (TK), lumbar lordosis (LL), sagittal vertical axis (SVA), pelvic tilt (PT), sacral slope (SS), and pelvic incidence (PI).This study was funded by a Small Exploratory Research Grant from the Scoliosis Research Society. Each subject was instructed and observed to stand in three different positions: pelvic resting, anterior pelvic rotation, and posterior pelvic rotation. Lateral standing radiographs were taken in each position and each image was examined by an orthopedic spine surgeon who digitally measured the TK, LL, SVA, PT, SS, and PI. The data were then statistically examined to determine the affect of pelvic position on each parameter.Subjects demonstrated a measurable, statistically significant change in each parameter with pelvic rotation. There was a clear pattern of change for LL, PT, and SS with the anterior and posterior pelvic rotations. A change in LL demonstrated a strong correlation with changes in all measured parameters with pelvic rotation.In asymptomatic subjects, pelvic motion affects the position of the spinal column and resultant spinopelvic parameters. The results of this study demonstrate that one can intentionally change the position of the pelvis and the adjacent spinal column in space. Knowledge of this relationship is important to the understanding of sagittal balance and could influence the treatment of patients with spinal deformity.