Biomechanical modeling and characterization of the postural parameters in adolescent idiopathic scoliosis

The focus of this Ph.D. project was to investigate the spino-pelvic biomechanical interaction in adolescent idiopathic scoliosis (AIS) more closely. Spine and pelvic kinematic, relative spino-pelvic orientation in static, and lumbosacral biomechanical loading were investigated in subjects with different curve patterns. We hypothesized that spino-pelvic interaction is not only different between AIS and controls, but also varies between subjects with different scoliotic types in static, kinematic, and biomechanical loading. Furthermore the hypothetical effect of the spinal operation on equilibrating the spino-pelvic biomechanical interaction was tested postoperatively.

Although the pelvic alignment in the AIS group was different from the age-gender matched control group, it is not closely verified to what extent the pelvic orientation and the spino-pelvic alignment affect the pelvis kinematic in subjects with different curve types and subsequently its impact on the spino-pelvic movement is not determined. An experimental setup was designed to investigate the pelvic 3D motion during simple trunk movement in vivo. Pelvic orientation was significantly different during three types of movement between the studied groups (p<0.001). Different pelvic range of motion in the anatomical planes was measured in the studied groups. Pelvic sagittal tilt and pelvic axial rotation were significantly different between the two scoliotic groups (p<0.05). The result suggests that pelvic initial alignment in the three anatomical planes plays an important role in determining the pelvic contribution to the maximum ROM in the scoliotic subgroups.

Although the main focus in diagnosing and evaluating the scoliosis is on the location and severity of the spinal deformities, different published literatures have shown the presence of a significant pelvic obliquity or rotation in scoliosis particularly in subjects with severe curves. However, the relationship between the pelvic orientation and spinal curves in subjects with different types of scoliosis was not characterized yet in 3D. In order to investigate this relationship, the lateral and postero-anterior radiographs of 80 main right thoracic (MT), 80 left thoraco-lumbar/ lumbar (TL/L), and 35 controls were obtained. 3D reconstruction of the spine and pelvis was generated from bi-planar radiographs of each patient. Pelvic 3D alignments were measured by means of the 3D coordinates of the left and right anterior and posterior iliac spine landmarks (ASIS and PSIS). A trapezoid was schemed by connecting these four points. The angle between the projections of the line connecting the midpoint of the ASIS and PSIS on each side on frontal and transverse planes and true horizontal and vertical axes were used to define the pelvic frontal tilt, and pelvic axial rotation respectively. The average pelvic orientation (absolute value) was measured respectively in frontal and transverse planes at 2.6°± 2 [range: -6°, 5°] and at 3.8°± 2 [-7°, 8°] in the MT group, and at 3.2°±1 [-8°, 4°] and at 4.4°±2 [-10°, 10°] in the TL/L group. While pelvic frontal tilt correlated to the position of the spinal curve in the frontal plane (the thoracic and lumbar segments) more than 70% of the scoliotic subjects in each group had their main thoracic and pelvis rotated in the same direction in the transverse plane (p<0.05). 91% of the controls had less than 1.8° pelvic obliquity [0°, 3°] and a non-significant 1.2° pelvic axial rotation [0°, 3°] in the transverse plane. The results highlighted a significant correlation between pelvic orientation and both thoracic and lumbar spinal deformities in frontal and transverse planes in the two AIS subgroups.

Finally a case study was performed to analyze the effect of the spinal surgery on the biomechanical loading of the sacrum in subjects with different types of scoliosis. The application of both spino-pelvic biomechanical and morphological parameters permitted to evaluate the biomechanical outcome of the surgical instrumentation of the spine. The effect of the spinal surgery on equilibrating the biomechanical loading of the sacrum and making it more similar to the values observed in controls was shown in the post-operative group. (Abstract shortened by UMI.)