What Is Spondylolisthesis? Causes, Symptoms & Imaging

Spondylolisthesis is a condition in which one of the bones of the spine, called a vertebra, slips forward over the bone directly beneath it. The name comes from Greek words meaning “spine” and “to slip,” which is a fair description of what happens: the normally stacked column of vertebrae develops a small step where one bone drifts out of position. It most often occurs low in the back, in the lumbar spine, where the body carries the most weight. For many people the slip is mild and causes no problems at all, and it is discovered only when the spine is imaged for another reason. Understanding what spondylolisthesis is — and what it is not — takes a good deal of worry out of a word that sounds far more alarming than the condition usually is.

The cause often depends on age. The most common form in older adults is degenerative spondylolisthesis, in which the discs and small joints gradually wear with time until one vertebra shifts slightly forward. Another common cause is spondylolysis, a small stress fracture in a thin bridge of bone at the back of the vertebra that can develop from repeated bending and arching; it is seen fairly often in young athletes in sports such as gymnastics, football, and weightlifting, and if the bone gives way on both sides the vertebra can gradually slide. Less commonly a person is born with a spine shaped in a way that makes slippage more likely, and injury can contribute as well. When symptoms appear they usually center on the lower back — a dull ache that worsens with standing, walking, or bending backward and eases with rest — and, if the slip narrows the space where nerves travel, pain, tingling, or numbness in the buttocks or legs. Clinicians grade the slip from I to IV, but the grade alone does not dictate how a person feels, which is why imaging is always read alongside symptoms.

Each imaging test contributes something different. A standing X-ray usually comes first because it shows the alignment of the bones and reveals the forward slip and its grade, and a CT scan adds fine bony detail including a clearer look at a suspected stress fracture. What MRI adds is a view of the soft tissues the others cannot show as well — the spinal canal, the discs, and the nerves themselves — with no ionizing radiation, which helps clarify whether the slip is narrowing the canal or pressing on nerve roots when leg symptoms are present. On a whole-body MRI a slip may simply turn up as an incidental finding noticed during broader screening rather than because of back pain; the scan establishes a baseline but is not a diagnosis, and any finding is meant to be reviewed with a physician. Most cases are managed without surgery through physical therapy, core strengthening, and activity adjustments. To learn more, explore the Whole Body MRI Scan in Charleston, read how we explain incidental findings on an MRI, or see the related entry on a bulging disk.