We investigate the biomechanics of various surgical treatments for spine disorders, such as fixation with instrumentation, osteotomies and correction of deformities by means of finite element modeling. Our models range from a single vertebra or motion segment to the whole thoracolumbar spine, including sacrum and pelvis for the biomechanical investigation of long fusions. Patient-specific numerical models are built based on state-of-the-art imaging techniques such as biplanar X-rays with the EOS Imaging System, available at IRCCS Istituto Ortopedico Galeazzi. We also employ software developed in-house for the creation of patient-specific models based on CT and MRI scans.