What Is the Pars Defect of the Lumbar Spine
Spondylolisthesis is the actual slipping forward of the vertebral body (the term "listhesis" means "to slip forward") (Fig. 3). It occurs when the pars interarticularis separates and allows the vertebral body to move forward out of position causing pinched nerves and pain. Spondylolisthesis usually occurs between the fourth and fifth lumber vertebra or at the last lumbar vertebra and the sacrum. This is where your spine curves into its most pronounced "S" shape and where the stress is heaviest.
Spondylolysis and Spondylolisthesis - Metro Pain
Spondylolysis (spon-dee-low-lye-sis) and spondylolisthesis (spon-dee-low-lis-thee-sis) are separate, yet related conditions. Spondylolysis usually comes first, though not always. The term comes from "spondylo," which means "spine," and "lysis," which means to divide. Spondylolysis is a breakdown or fracture of the narrow bridge between the upper and lower facets, called the pars interarticularis. It can occur on one side (unilateral) or both sides (bilateral) and at any level of the spine, but most often at the fourth or fifth lumbar vertebra (Fig. 2). If spondylolysis is present, then you have the potential to develop spondylolisthesis.
Three types of isthmic spondylolistheses are recognized:a. a stress (fatigue) fracture of the pars interarticularis - lyticb. an elongated but intact pars interarticularisc. an acute fracture of the pars interarticularisThe lytic (subtype a) results from the separation or dissolution of the pars.