Characterizing Pelvis Dynamics in Adolescent With Idiopathic Scoliosis

Study Design. Pelvic dynamic analysis in adolescents with idiopathic scoliosis (AIS). Objective. To examine and characterize pelvis dynamics in AIS. Summary of Background Data. Although studies have examined spine and pelvis postural differences between female adolescents with and without scoliosis much is still unknown about the dynamics of pelvis in trunk-pelvic interaction and how the type of scoliosis compromises pelvic mobility consequently affecting the overall dynamics of the trunk-pelvis kinematic chain. Methods. A total of 25 female AIS (18 right thoracic: RT and 7 right thoracic-left lumbar: RTLL) and 12 controls were recruited. Reflective markers were placed on the trunk and pelvis and their trajectories were recorded using a 5-camera motion capture system. Three trials were carried out, one for each of the various trunk-pelvis movements (flexion/extension, lateral bend, and axial rotation on either side) performed by the subjects. Results. Pelvic alignment in the 3 planes were significantly different for all movement types (P < 0.001), with distinct differences in pelvic sagittal tilt and transverse plane rotation, particularly during lateral bending and axial rotation in patients with RT and LL curves (P = 0.035, P = 0.006, respectively). A majority of the patients from the 2 scoliotic groups had the pelvis rotated to the side of the major curve (right). Although RT subjects had similar dynamic pelvic responses as the controls, the RT-LL patients had relatively more pelvic sagittal tilt during lateral bending and axial rotation toward the major curve. Conclusion. In AIS, the initial three-dimensional alignment of the pelvis (sagittal and frontal tilt, transverse plane rotation) plays an essential role in dictating the biomechanics of the pelvis for any movement type. A spatial concurrency in pelvic alignment was noted wherein a change in 1 parameter will affect the remaining 2. Increased pelvic sagittal tilt in the RT-LL subjects was substituted by more pelvic rotation in the RT subjects during trunk flexion/extension. Differences in pelvic dynamics in AIS are not evident in discrete parameters, for example, total ranges-of-motion but more so in its biomechanics during the movement, which in turn is dictated by the initial alignment of the pelvis.