What Is Bertolotti Syndrome, and Why Was It Missed?

What is a lumbosacral transitional vertebra?

A lumbosacral transitional vertebra (LSTV) is a bone at the very bottom of the spine. It does not look quite like a normal lumbar vertebra or a normal sacral segment. Instead, it sits somewhere in between. The lowest lumbar vertebra (usually called L5) may have an enlarged side process. This forms a partial or complete bony bridge to the sacrum below. This is called sacralisation of L5. In other cases, the top segment of the sacrum separates and behaves more like a lumbar vertebra. This is known as lumbarisation of S1.

Both are common. Many people have one and never know, because it causes no symptoms at all. When an LSTV does cause pain, usually on one side of the lower back, that is Bertolotti syndrome.

What does Bertolotti syndrome feel like?

The main sign is lower back pain on one side, often just above the belt line. It starts in the late teenage years or early adulthood. It tends to get worse with activity and ease with rest. The abnormal joint (sometimes called a pseudoarthrosis) can irritate nearby structures, so pain may also spread into the buttock or leg.

These symptoms overlap with disc problems and SI joint dysfunction. So Bertolotti syndrome is rarely the first thing considered.

Why is Bertolotti syndrome so often missed?

The biggest single reason is an error in counting the vertebrae. When you have a transitional vertebra, the normal numbering system breaks down. Most standard lumbar x-rays and MRI scans only show the lower part of the spine. Without seeing the full picture from top to bottom, the reporting clinician cannot reliably count down from C1. They might label your transitional L5 as a normal sacral segment, or label S1 as L5. That error of one level can mean the wrong disc, the wrong joint or the wrong nerve root is named as the problem.

Research suggests that numbering errors happen in a significant proportion of patients with a transitional vertebra when only a limited lumbar scan is done. This matters most if an injection or surgery is planned. Targeting the wrong level can mean the procedure fails, or a normal structure is treated without need.

How does a standing full spine scan help diagnose Bertolotti syndrome?

A standing full spine image captures every vertebra, from the base of the skull to the pelvis, in a single exposure while you carry your full body weight. This gives the reporting clinician two things that limited scans cannot.

Accurate counting of the vertebrae. With every vertebra visible, the clinician counts from C1 at the top all the way down. A transitional vertebra becomes obvious, rather than hidden at the edge of a cropped image.

Alignment under body weight. The body is a connected chain. A bony bridge on one side of L5 can tilt the pelvis, shift the spine sideways and force other areas to compensate. These shifts only appear when you are standing. Lying down relaxes the muscles and removes gravity. This often hides the very imbalance that is driving your pain.

At ScanAlign, unstitched full-body standing imaging uses EOS technology to capture this full view with about 90% less radiation than a standard x-ray, around ten times less. The image is a single, unstitched exposure, not several smaller x-rays joined together. This means no overlap errors and reliable measurement from head to pelvis.

What can be done once Bertolotti syndrome is confirmed?

The first and most important step is an accurate diagnosis. ScanAlign is a diagnostic imaging clinic, not a treatment provider. The role of the standing scan is to give you and your clinician a precise map of your anatomy. Once the transitional vertebra is confirmed and correctly numbered, your treatment team can make informed decisions.

Common treatment options, guided by your specialist, may include physiotherapy to strengthen the surrounding muscles, guided injections at the correct joint to confirm the source of pain, or, less commonly, surgery at the correctly identified level. The key point is that every one of these options depends on knowing exactly which bone and which joint is responsible. A numbering error can send treatment in the wrong direction completely.

If you have been told your scans are normal but you still have persistent one-sided back pain, it may be worth asking whether the full spine was visible and whether a transitional vertebra was considered. You can book a full spine standing scan without a referral from your doctor.

Before you start treatment, or change the one you are on, it is worth getting a detailed diagnosis. Knowing whether the cause sits in the pelvis, the legs or the spine changes what will actually help.

Frequently asked questions about Bertolotti syndrome