Scoliosis is a musculoskeletal disorder seen all around the world. It affects both the alignment of the vertebra and intervertebral disc. Scoliosis can be treated conservatively with a cast and brace or surgically with spinal instrumentation. During planning for surgical instrumentation, several factors need to be considered. Among those, biomechanical changes in the non-scoliotic vertebrae and discs are important. This is vital in determining the future degenerative changes of the spine. For this reason, this study was conducted with a finite element model of the lumbosacral joint using CT scan files to find the total deformation and equivalent static strain of the lumbosacral disc between pre and post-operative thoracic scoliosis patient. From the results, it is evident that there is a biomechanical change in the lumbosacral disc and structural change in the vertebral alignment followed immediately after corrective surgery. The correction in the alignment of the scoliotic spine brings changes to the biomechanical functionality and load-bearing capacity of the lumbosacral intervertebral disc before and after surgery.