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Aging Spines Speak to the Realities of "Pars Defects" in the Low Back

Back in the 1950s, one doctor began a study of the spines of first graders. Dr. Daniel Baker took spine X-rays of 500 six-year-old children in a northern Pennsylvania town over three years. He was looking for a condition called spondylolysis. Spondylolysis is a defect or fracture in the pars interarticularis (also just called the pars) of the vertebra.

The pars is an area in the protective bony ring on the back of the spinal column. There is one pars on the left and one on the right of each vertebra. A bony defect here can actually create a separation in the bone. If the condition happens on both sides of the bony ring, the vertebra can slip forward over the one below it. This slippage is called spondylolisthesis.

This study has continued since the 1950s. It has followed the children into adulthood over a span of 40 years. This gives an idea of the natural history of this condition over time. Doctors and parents want to answer several questions: Will spondylolysis always develop into spondylolisthesis? Can a defect of this type heal on its own? Are sports and physical activities allowed?

Out of the 500 children, 22 had spondylolysis by age six. Healing occurred in some children who only had the defect on one side of the bone. This is called a unilateral defect. Unilateral defects never slipped. Subjects with this type of spondylolysis only reported mild low back pain (if any at all).

Knowing if and when future slippage will occur is hard to guess. The authors report that having the defect on both sides (bilateral defect) increases the risk of slippage. Slippage, if it is going to occur, appears to occur at a faster rate before adolescence, and it tends to slow with age.

This study tells us that spondylolysis is usually a benign (not a serious) condition. Slippage can occur if the defect is present on both sides. However, most people with a pars defect live without pain and are able to do all activities. The authors say that doctors should not advise against sports just because a person happens to have spondylolysis or a minor slippage (spondylolisthesis).

References: William J. Beutler, MD, et al. The Natural History of Spondylolysis and Spondylolisthesis. In Spine. May 15, 2003. Vol. 28. No. 10. Pp. 1027-1035.

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