This study aims to understand the impact forces that surgeons apply to the human spine during a posterior spinal fusion procedure towards the development of a novel spine surgical simulator for training medical residents. The foci of this study are impact forces during graft placement and spinal interbody cage insertion. This study examined the lumbar intervertebral discs of two male cadaveric specimens. Impact forces were collected during graft and spinal cage insertion over multiple levels. An impulse hammer and a camera were used to collect impact forces and displacements, respectively. The results demonstrated a logarithmic relationship between impact forces and cumulative displacement during graft placement. This was also observed between cumulative displacement and number of impacts during spinal cage insertion. A linear relationship was observed for the impact forces and number of impacts during graft placement. Results suggest that surgeons rely on the feedback experienced from impact forces during graft insertion to gauge the amount of graft that was placed in a specific area of the disc. Impact forces during cage insertion provide information about any encountered obstacles. When developing surgical simulators, designing the force feedback system should require modelling these behaviors to effectively impart corresponding skills on a trainee.