The Pathomechanism of Spondylolytic Spondylolisthesis in Pediatric Lumbar Spines: In Vitro and Finite Element Assessments

Experimentally, it was determined that the weakest link for A-P shear force in the immature baboon lumbar spine with pars interarticularis defects was between the growth-plate and osseous end-plate, even with an injured disc. Immature baboon finite element models (FEM) as well as an immature human FEM were developed. Numerical results predicted that a thin pars will increase stresses at the pars, eventually leading to a pars defect. Furthermore, a fracture in the pars interarticularis results in substantially greater loads being carried by the growth-plates. Upon combination of the experimental and numerical aspects of this study, it is possible to predict the A-P shear force needed for spondylolisthesis to occur.