Spondylolisthesis

Spondylolisthesis is when one vertebra slips forward over the one below it. It happens most often in the lower back. When a vertebra slips backwards instead, the same problem is called retrolisthesis. On a scan report you may simply see listhesis, meaning a vertebra out of line with the one below, or anterolisthesis for a forward slip. The slip itself is only part of the picture: what matters is what caused it, how far it has moved, whether it is stable, and whether it is pressing on any nerves.

Many people have a slip and no symptoms at all, and the size of the slip does not reliably predict how much pain it causes. A small slip can be painful and a larger one can be silent, which is why the scan is always read alongside how a person actually feels.

There are a few different causes, and the two that matter most in practice are:

• Isthmic spondylolisthesis. A small stress fracture or defect in a part of the vertebra called the pars interarticularis lets it slip. It often starts in youth, particularly in sports that repeatedly arch the lower back such as gymnastics, cricket, or weightlifting, and may not cause symptoms until adulthood.
• Degenerative spondylolisthesis. Age-related wear of the discs and facet joints loosens the segment and lets a vertebra drift forward, most often at L4/L5. It is more common with age and in women, and the slip is usually low-grade.

Less common causes include a slip present from birth (congenital or dysplastic), a slip from a fracture (traumatic), and one caused by disease weakening the bone (pathological). Because spondylolisthesis so often sits alongside wear in the discs, joints, and canal, it frequently travels with other conditions.

A slip is measured on a standing side-on X-ray using the Meyerding scale, which grades it by how far one vertebra has slipped over the one below, expressed as a percentage.

Grade I: up to 25% of the way forward. This is the most common, and most degenerative slips stay here.
Grade II: 25 to 50%.
Grade III: 50 to 75%.
Grade IV: 75 to 100%. A vertebra that has slipped right off the one below, beyond 100%, is called spondyloptosis.

The grade guides treatment: low-grade slips (Grade I and II) are usually stable and often managed without surgery, while higher grades are more likely to need stabilising. It does not, by itself, predict pain, a Grade I slip can be painful and a higher one can cause few symptoms, so how you are affected matters as much as the number.

When spondylolisthesis needs surgery, the choice depends on the type of slip, its grade, whether it is stable, and whether it is pressing on nerves. The main options are:

Spondylolisthesis covers a wide range, from a stable, low-grade slip that may never need surgery to an unstable one that does. Where a slip is stable and low-grade, we look first at whether decompression alone or a motion-preserving option fits. Where it is unstable or advanced, a fusion is the right choice, and the priority is to do it in the least invasive way that will hold.

Dr. Tayard Buranakarl is a senior spine surgeon at the Bangkok Spine Academy and Bangkok International Hospital, and a Key Opinion Leader for Medtronic. He trained internationally, including a fellowship at UCLA, and introduced several minimally invasive fusion techniques in Thailand, among them OLIF, which he uses to treat spondylolisthesis through a small side approach that spares the back muscles.