Abstract
This study is concerned with the mechanical instability of isthmic spondylolisthesis. The effects of isthmic defect on the structural stiffness of lower lumbar spine are discussed by using finite element analyses. The structural stiffness of lower lumbar spine was examined by the load-deformation relations in vertical direction using an intact, L4-defect and L5-defect lumbar spine models. The results showed that the structural stiffness of L4-defect lumber spine was lower than those of intact and L5-defect lumbar spines. There was no significant difference between the stiffness of intact and L5-defect lumbar spines. The decrease of the structural stiffness may be attributable to the mechanism of isthmic spondylolisthesis.
