Our 17-year old daughter had surgery to fuse the bottom of her spine because L5 was slipping forward over her sacrum. The X-rays show she’s had some more slippage since the operation. Is this a sign that the surgery didn’t work?

The condition you describe is called spondylolisthesis and can range from mild to severe. The degree of severity is based on how far forward the vertebra has slipped. More than a 50 per cent slip is called a high-grade spondylolisthesis.

Fusion of the spine is needed in high-grade cases to prevent or stop pain and disability. Further slippage is called slip progression. If this happens after the fusion, it’s referred to as settling rather than slip progression.

A small amount of slippage or settling is common. It’s not considered a failed fusion if there is no movement seen on dynamic X-rays. The X-rays must be taken as the patient bends forward and straightens into a slightly extended position of the spine.

Further slippage is not expected. In rare cases, a second revision operation may be needed.