Intraoperative three-dimensional biomechanics of scoliosis instrumentation

This thesis addresses the problems of measuring vertebral kinematics during scoliosis surgery and what the data means to surgeons. Adolescent idiopathic scoliosis is a complex three-dimensional deformity of the spine. Understanding the deformity and its surgical treatment, requires a measurement technique that will allow surgeons to fully appreciate the deformity and the treatment strategies used. Most methods of assessing the deformity available introduce radiation exposure to the patient and are not useful for measuring scoliosis changes during surgery. A new method for analysis of surgical techniques for the correction of scoliotic spine deformity is introduced in this work.; This technique uses a dual overhead stereo camera system in the operating room to take photographic pairs at specific stages during the spinal surgical procedure. In this way, the effects of specific surgical manoeuvres of the spine and instrumentation can be measured. The photographic pairs are transferred to a computer graphics workstation and manually digitized to calculate three-dimensional coordinates for posterior aspects of the each visible vertebra. Three-dimensional changes in position occurring after specific stages of surgical instrumentation are compared. Rotational and translational data are calculated with respect to the patient's pelvis. The three-dimensional kinematic rotations and translations of the vertebrae are reported for thirty-five female patients with right thoracic adolescent idiopathic scoliosis.; The results of this study show dud the surgery corrected the coronal plane scoliotic deformity by lateral translation of the apical vertebrae toward the midline and rotation of the end vertebrae around the sagittal axis. The sagittal plane deformity was corrected by posterior translation of the apical vertebrae and by rotation of the end vertebrae around the coronal axis.; This study showed that the end vertebrae rotate through angles of equal magnitude but in opposite directions around a unique axis for each vertebra. The apical vertebrae translated toward the midline via the surgical “derotation manoeuvre” to correct the lateral deformity as well as re-creating the lost kyphosis. This new knowledge of the deformity suggests that future surgical correction should focus on the concept of a helix, with less emphasis on “de-rotation” of the apical vertebrae but focus on rotating the end vertebrae instead.