Patient positioning for surgeries of the spine: How does it impact spinal geometry and how can it be exploited to improve surgical procedures

This project was done in parallel with the design and construction of a new Multi-Functional Positioning Frame (MFPF) for spinal surgeries which allowed for lower limb positioning and thoracic vertical displacement. The MFPF itself was a combination of two previously developed surgical positioning devices: the Dynamic Positioning Frame (DPF) (allowing thoracic cushion adjustment and corrective force application) and the "leg positioner" (allowing hip flexion and extension). Finite element modeling (FEM) was previously used to study patient positioning on the DPF.;It was hypothesized that: 1) a FEM of the human spine, thoracic cage, pelvis, and relevant adjacent structures can simulate the geometric effects, on the spine, resulting from a patient moving from a standing position to a prone position on the MFPF with a coronal and sagittal plane Cobb angle accuracy of 5° for a segmental curve; 2) leg positioning has an important impact on the geometry of the spine. Manipulation of a patient's leg position while on the MFPF can modify lumbar lordosis by +25%, -40%, thoracic kyphosis by +20%, -10%, and reduce the primary coronal plane Cobb by 10% relative to a neutral prone position; and 3) the combined use of the MFPF positioning features has an important impact on the geometry of the spine which can be utilised intra-operatively to facilitate spinal instrumentation procedures.;Experimental testing yielded the following results: 1) Prone positioning on the MFPF resulted in a significant loss in Main Thoracic (MT) and Thoraco-Lumbar/Lumbar (TL/L) Cobb angles, a significant loss in lordosis and an important loss in kyphosis. 2) Lower limb positioning on the MFPF had a significant impact on both sagittal curves of the spine. Hip flexion resulted in reduction of lordosis and kyphosis and hip extension resulted in increases in lordosis and kyphosis. 3) Vertical displacement of the sternum on the MFPF had a significant impact on both sagittal curves of the spine. Raising the sternum resulted in a significant increase in kyphosis and lordosis in addition to an increase in intervertebral disc space in the apical thoracic segment. 4) Lateral leg displacement on the MFPF allowed for a significant reduction of Cobb angle and Apical Vertebral Rotation (AVR) in the lowest structural curve by lateral displacement of the lower limbs towards the scoliotic spine convexity. 5) Pelvic torsion on the MFPF allowed a significant reduction in Cobb angles and important reductions in AVR by raising the pelvis on the concave side of their lowest structural curve and opposite thoracic cushion.;FEM simulations of prone positioning, hip flexion/extension, and combined positioning including thorax vertical displacement, thorax lateral displacement, lower limb lateral displacement and pelvic torsion yielded the following results: 1) The FEM developed was able to reproduce segmental curve reductions due to prone positioning on the MFPF within 5°. 2) Patient and surgical frame parameters such as standing segmental curves and relative vertical position of thoracic cushions had an important impact of spinal geometrical changes due to prone positioning while the relative longitudinal position of the thoracic cushions had no impact. 3) The FEM developed was able to reproduce sagittal curve changes due to lower limb positioning on the MFPF within 5°. 4) Lower limb positioning between limit physiological positions (30° of extension to 90° of flexion) resulted in a relatively linear decrease in lordosis and kyphosis (an average of 84% (59°) and 34% (13°)) which is most influenced by flexibility of the hamstrings during flexion. 5) Combined use of the MFPF features offered a wider range of possible intra-operative spinal geometrical manipulation as compared to their individual use which was dependent on scoliotic curve type. 6) A method for determining patient positioning on the MFPF allowed for global optimization of spinal geometry based on the needs of individual surgeons.;Use of the MFPF positioning features allowed for a wide range of spinal geometrical parameters to be manipulated. Several of its novel positioning features have great potential for the improvement of spinal instrumentation procedures by offering surgeons a wider range of possible intra-operative geometries. The FEM developed allowed for the detailed study of existing surgical positions as well as aided to develop some new ones. Finally, the FEM allowed for optimization of the combined use of multiple surgical positions. (Abstract shortened by UMI.)...