What it means
The pars interarticularis is a narrow strip of bone in the ring at the back of each vertebra, between the joints above and below. Repeated bending backward, as in gymnastics, diving or weightlifting, can stress it until it cracks. It is most common at L5, the lowest lumbar vertebra, and can affect one side or both. MRI can show early stress in the bone before a crack forms, and CT shows the gap best.
When it matters
In adults, a pars defect is often old, causes no trouble and is found by chance. In teenagers and young athletes with low back pain, a recent stress injury matters more, because it can often heal when found early. Doctors also check for a forward slip of the vertebra (spondylolisthesis), which can develop when both sides are cracked. Follow-up imaging depends on age, activity and symptoms.
Questions to ask your doctor
- Is the defect on one side or both, and at which level?
- Does it look recent and able to heal, or old and settled?
- Is there any slip of the vertebra that should be watched?
