Spondylolysis happens when a crack forms in the bony ring on the back of the spinal column. Most commonly, this occurs in the low back. In this condition, the bone that protects the spinal cord fractures as a result of excessive or repeated strain. The area affected is called the pars interarticularis, so doctors sometimes refer to this condition as a pars defect.


This condition appears in six percent of children. It mainly affects young athletes who participate in sports in which the spine is repeatedly bent backwards, but it can affect workers who engage in back bending job duties as well.

Although spondylolysis can affect people of any age, children and adolescents are most susceptible. This is because their spines are still developing, and the pars is the weakest part of the vertebra. Placing extra strain on this area of the spine during childhood increases the chance that a pars defect will occur. Many individuals with spondylolysis will develop spondylolisthesis, which is usually the forward displacement of a vertebral bone over the vertebrae beneath it.

Anatomy of spondylolysis.

The human spine is made of 24 spinal bones, called vertebrae. Vertebrae are stacked on top of one another to create the spinal column. The spinal column gives the body its form. It is the body’s main upright support. The section of spine in the lower back is called the lumbar spine.

Each vertebra is formed by a round block of bone, called a vertebral body. A circle of bone attaches to the back of the vertebra. When the vertebrae are stacked on top of each other, these bony rings create a hollow tube. This tube, called the spinal canal, surrounds the spinal cord as it passes through the spine. Just as the skull protects the brain, the bones of the spinal column protect the spinal cord.

The protective ring that surrounds the spinal cord is a continuous ring of bone. Its sections include two pedicles which attach directly to the back of the vertebral body. Two laminae complete the ring.

The pedicles and laminae are two different areas of the bony ring. The area between them is not a joint. Rather, it is a location in the continuous ring of bone that doctors call the pars interarticularis, or “pars” for short. There are two such meeting points on the back of each vertebra, one on the left and one on the right. The pars is thought to be the weakest part of the bony ring.

McCormick Law Office in Milwaukee, Wisconsin handles low back workers compensation claims involving spondylolysis, where there are other factors implicating a work-related lumbar injury or condition, such as job duties and other signs of degeneration.