Q: My 23-year-old daughter has been diagnosed with a low-grade spondylolisthesis. I understand this is a slippage of the 5th lumbar vertebra forward over the sacrum below it. What does low-grade mean and what are her chances for recovery?

A: Spondylolisthesis refers to a defect in the vertebral bone. A crack in the pars interarticularis (supportive column) of the vertebra causes a separation of the main body of the bone from the back half where the spinal cord and spinal nerve roots are located.

The vertebral body shifts forward over the stable vertebra below. The result is a pulling, traction pressure on the nerve tissue and neurologic symptoms. X-rays taken from a side view show characteristic changes that identify this condition.

Low-grade means there is less than 50 per cent slippage of the top vertebra over the bottom vertebra. In your daughters case, it's the last lumbar vertebra (L5) over the sacrum (S1) below. Slippage is measured using X-rays to see how far forward the vertebra body has moved. The most commonly used grading system to measure severity of slippage is based upon measurements of the distance from the posterior (back) edge of the superior (top) vertebral body to the posterior edge of the adjacent inferior (below) vertebral body (or sacrum). This distance is then reported as a percentage of the total superior vertebral body length.

Grade one means the top vertebra has slipped less than 25 per cent forward over the bottom vertebra (or in your daughter's case L5 over the sacrum). Grade two refers to a 25 to 50 per cent slippage. Grade three is 50 to 75 per cent. Grade four goes from 75 per cent slippage to 100 per cent when the vertebra completely falls off the supporting vertabra or sacral base (very rare). Low-grade is the same as Grades one and two (less than 50 per cent slippage).

Conservative (nonoperative) treatment can be very successful for many patients with low-grade spondylolisthesis. Postural and strengthening exercises are often recommended. Patients must be educated about their condition and the need to keep up their exercises indefinitely. But these only take five to 10 minutes three to four times a week. If conservative care fails, then surgery to fuse the spine at that level may be necessary.

Reference: Jin-Sung Kim, MD, et al. Which Lumbar Interbody Fusion Technique is Better in Terms of Level for the Treatment of Unstable Isthmic Spondylolisthesis? In Journal of Neurosurgery: Spine. February 2010. Vol. 12. No. 2. Pp. 171-177.