What are the Differences Between Spondylolysis and Spondylolisthesis?
Spondylolisthesis and spondylolysis are different spinal conditions but they are often related to each other. Spondylolysis is a crack or stress fracture that develops through the pars interarticularis, which is a small, thin portion of the vertebrae that connects the upper and lower facet joints. The pars interarticularis is the weakest part of the vertebrae. Due to this weakness, it is the area most vulnerable to injury from the repetitive stress and overuse. Spondylolysis is most commonly seen at the L4 and L5 levels. When spondylolysis is left untreated it can lead to spondylolisthesis.
Spondylolysis can weaken the vertebrae so much that it is unable to maintain its proper alignment in the spine. In spondylolisthesis, the fractured pars interarticularis separates allowing the injured vertebrae to shift forward onto the vertebrae directly below it. Spine doctors classify spondylolisthesis as either low grade or high grade depending upon the amount of shift. A high-grade shift occurs when more than 50% of the width of the fractured vertebra slips forward on the vertebra below it. Patients with high-grade slips are more likely to experience significant pain and nerve injury and typically need surgery to alleviate pain.