Date of Award


Document Type


Degree Name

Master of Science (MS)


Biomedical Engineering and Imaging


Orthopaedic Surgery

Research Advisor

William M. Mihalko, M.D., Ph.D.


Denis J. Diangelo, Ph.D. John L. Williams, Ph.D. Audrey R. Zucker-Levin, Ph.D., PT, GCS, MBA


Fixed Sagittal Imbalance, Flatback, Kinematics, Lumbar, Pelvis, Validation


Americans are undergoing spinal fusion surgery (SFS) at an ever increasing rate; in 2008 over 400,000 Americans underwent SFS with a national cost of approximately $33.9 billion. During SFS it is difficult for the surgeon to properly align the spine’s s-shape, as viewed from the patient’s side. Abnormal alignment of the spine then alters the position of the pelvis and hip joints, which may impact the function and hip contact patterns. Several studies have shown that patients with spinal pathology, such as arthritis, often have a coexisting hip pathology or subsequently develop hip pathology, and it is estimated that 18% of individuals undergoing total hip arthroplasty (THA) have concurrently developed a lumbar spine disorder. If the THA patient then undergoes SFS, any abnormal alignment of the spine can then impact the function and survivorship of the THA. The goal of this study was to examine the influence of altered sagittal lumbar lordosis on sagittal pelvis kinematics during activities of daily living including gait, sit-to-stand, and standto-sit. We hypothesized that a subject would compensate an altered lumbar lordosis by manipulating their pelvic tilt and torso alignment to maintain a normal plumbline. To investigate this hypothesis 10 healthy subjects (6 female, 4 male), aged 18-35 years, with no back, spine, or lower extremity injuries or surgeries were evaluated during static stance, gait, sit-to-stand, and stand-to-sit. Subjects performed activities in a 3-D motion analysis lab, with and without the use of a hyper-tensioned clavicle strap. An EOS bi-planar x-ray system was used to validate marker placement, as well as spinal and pelvic changes induced by the hypertension clavicle strap. Each subject also underwent a standard physical therapy exam to determine any functional limitations or abnormalities. Subjects were then evaluated in a paired fashion. Changes in pelvic tilt and hip flexion were correlated to changes in lumbar lordosis, plumbline, and trunk-pelvic angle. When different groups were present, the statistical coincidence of each linear regression was tested. For each condition a Wilcoxon signed-rank test was used to determine if each of the aforementioned parameters significantly changed from normal. This study found that decreasing lumbar lordosis by (mean ± SD) 4 ± 2 deg during gait did not significantly alter pelvic tilt. However, subjects with clinically tight hamstrings responded significantly different to a hyper-tensioned clavicle strap. Similarly, -5 to 9 deg change in lumbar lordosis did not correlate with changes in pelvic tilt during sit-to-stand or stand-to-sit activities. Changes in plumbline were found to be the best predictor for changes in pelvic tilt at peak hip flexion during stand-to-sit and sit-to-stand activities, exhibiting a nearly 1:1 relationship.