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 that 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 that 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, 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 hallmark is one-sided lower back pain, often just above the belt line, that starts in late adolescence or early adulthood. It tends to worsen with activity and ease with rest. Because the abnormal joint (sometimes called a pseudoarthrosis) can irritate nearby structures, pain may also spread into the buttock or leg.

Because these symptoms overlap with disc problems and SI joint dysfunction, Bertolotti syndrome is rarely the first thing considered.

Why is Bertolotti syndrome so often missed?

The single biggest reason is a vertebral counting error. 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 from C1 downwards. They might label your transitional L5 as a normal sacral segment, or label S1 as L5. That one-level error can mean the wrong disc, the wrong joint, or the wrong nerve root is identified as the problem.

Research suggests that vertebral numbering errors occur in a significant proportion of patients with a transitional vertebra when only a limited lumbar scan is performed. This matters most if an injection or surgery is planned, because targeting the wrong level can mean the procedure fails or a normal structure is treated unnecessarily.

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 bear your full body weight. This gives the reporting clinician two things that limited scans cannot.

Accurate vertebral counting. 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.

Weight-bearing alignment. 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, often hiding the very asymmetry 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 stitched together, which 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, so the role of the standing scan is to give you and your clinician a precise map of the anatomy. Once the transitional vertebra is confirmed and correctly numbered, your treatment team can make informed decisions.

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

If you have been told your imaging is 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 GP referral.

Frequently asked questions about Bertolotti syndrome