Studies have shown that scoliosis curves correct when patients are positioned on the operating table prior to instrumentation. However, biomechanical aspects of positioning have not been widely studied. The objective of this study was to simulate patient positioning during instrumentation surgery and test various adjustment parameters of the trunk and recommend optimal patient positioning prior to, and during spine surgery based on the results of finite element simulations. A scoliotic patient was simulated using a finite element model and six different positioning parameters were modified while ten geometric measures were recorded. Statistical analysis determined which model parameter had a significant effect on the geometric measures. Geometric measures were individually and simultaneously optimized, while corresponding model parameters were documented. Every model parameter had a significant effect on at least five of the geometric measures. When optimizing a single measure, others would often deteriorate. Simultaneous optimization resulted in improved overall correction of the patient's geometry by 75% however ideal correction was not possible for every measure. Finite element simulations of various positioning parameters enabled the optimization of ten geometric measures. Positioning is an important surgical step that should be exploited to achieve maximum correction.