Degenerative Spondylolisthesis Model (L4-5). This is our LxD Model with a grade 1 anterior spondylolisthesis. With an intact pars demonstrate the degenerative nature of the facets and the most common form of spondylolisthesis. A stiff but dynamic one part disc allows motion at this one level to show how the spinal canals will narrow in extension and open in flexion. This model can be very helpful in the explanation of symptoms associated with spinal stenosis. The model can help explain why sitting (spinal flexion) may be relieving of stenosis symptoms and why walking (spinal extension) may increase symptoms. Optional shortened cauda equina.