The pars that incurs a stress fracture most likely has a hereditary predisposition to fracture. This means that the patient is born with some minor abnormality or weakness of the pars such that repetitive extension causes a fracture. For children without the predisposition, performing the same activities does not cause a stress fracture. Similarly, if the child with the predisposition never performed extension of the spine, the pars defect would never occur. Isthmic spondylolisthesis has never been detected in non-ambulatory patients.
Degenerative spondylolisthesis is a forward slippage secondary to arthritis of the spine.
Spinal stenosis is highly associated with this process. Motion therefore occurs on a microscopic level. The most common region for degenerative spondylolisthesis is L4-5. Traumatic spondylolisthesis is a slippage caused by a fracture in the spine, usually at the facet joint. The disruption of the bone allows the slippage.