Optimized use of multi-functional positioning frame features for scoliosis surgeries.

A multi-functional positioning frame (MFPF) has been developed which includes a number of positioning features allowing for hip flexion and extension, thorax vertical displacement, lateral leg displacement, pelvic torsion and thorax lateral displacement. The objective of this study was to develop a method allowing for optimized combined use of the MFPF features. Finite element models (FEMs) representing the osseo-ligamentous structures of the spine, ribcage, pelvis and lower limbs, including muscles, were created for three different curve types (main thoracic, double major, and triple major) using a radiographic bi-planar reconstruction technique. Each FEM was subjected to an experimental design in which MFPF features were independently and simultaneously varied between extreme positions and the resultant changes in spinal geometry measured. Optimization of individual spinal geometrical parameters showed variability between curve types and some patterns such as minimum Cobb with lower limbs displaced laterally towards the convexity, pelvis raised on the side of concavity, and thorax laterally displaced towards the thoracic concavity. A weighted and normalized global optimization equation was developed which accounts for the relative importance and desired values of each geometrical parameter. Combined use of MFPF features and adjustments offers a wider range of possible intra-operative spinal geometries than their individual use.