<unk>  is a bony defect or fracture within the pars interarticularis of the vertebral arch in the spinal column. The vast majority of<unk>  occur in the lumbar vertebrae, however it can also be seen in cervical vertebrae. The lumbar vertebra consist of a body, pedicle, lamina, pars interarticularis, transverse process, spinous process and superior and inferior articular facets, which form joints that link the vertebrae together. When examining the vertebra, the pars interarticularis is the bony segment between the superior and inferior articular facet joints located anterior to the lamina and posterior to the pedicle. Separation of the pars interarticularis occurs when<unk>  is present in the spinal column.<unk>  is typically caused by a stress fracture of the bone, and is especially common in adolescents who over-train in activities. The pars interarticularis is vulnerable to fracture during spinal hyperextension, especially when combined with rotation, or when experiencing a force during a landing. This stress fracture most commonly occurs where the concave lumbar spine transitions to the convex sacrum (L5-S1). A significant number of individuals with<unk>  will develop spondylolisthesis, which is true for 50-81% of this population. Pars interarticularis marked with red lines
Spondylolysis
Spondylosis
Spondylosis deformans
Spondylitis
Osteoarthritis
Spondyloarthropathy
Ankylosing spondylitis
Spondylodiscitis