Lumbar spinal stenosis (LSS) is the narrowing of the spinal canal, which often results in compression of the nerve roots or spinal cord. It creates significant pain and disability and is the most common reason for lumbar surgery within the United States for patients 65 years of age or older. Previous studies have shown that lumbar laminectomy outperforms nonoperative treatment of LSS. In some cases, however, fracture at the pars interarticularis (PI) occurs at the level of laminectomy, causing translation of the treated spinal segment over the adjacent segment, a complication known as iatrogenic spondylolisthesis. In addition, adjacent segment disease (ASD) has been reported to develop with an incidence rate of 10%, requiring reoperation after an average of 4 years. Therefore, the objective of the study is to provide surgeons with the quantified biomechanical effects of laminectomies on the PI, facet joints, intervertebral disc (IVD) and range of motion (ROM) as to enable them to reduce the risk of iatrogenic spondylolisthesis and better understand why ASD develops. To accomplish this, finite element (FE) models of three cadaveric specimens were created to simulate three laminectomy types with varying degrees of bone removal:​ single-level laminectomy (SLL), two-level laminectomy (TLL), and ventral-to-dorsal resection (VDR) with 0, 25, 50, and 75%. The models mesh, material properties, and boundary conditions were determined in a previous study. A 7.5-Nm torque was applied to produce flexion, extension, lateral bending, and axial rotation. Results indicated that stress at the PI increases with bone removal. Axial rotation produced the highest stress at the PI, approaching the range of cortical bone ultimate strength at the 75% bone removal. In addition, the facet- joint-forces (FJF) decreased from intact to 75% bone removal in all laminectomy types and ROMs. Disc stress trends varied from subject to subject and ROM experienced little to no effect postlaminectomy. The effects seen in FJF and IVD stresses further reflect that the remainder of the spine must experience compensatory biomechanical changes as a result of surgical intervention. Lastly, it was concluded that laminectomies up to 50% can be considered generally conservative, while a 75% laminectomy presents a great risk of iatrogenic spondylolisthesis.