Bertolotti Syndrome

A plain-language guide to what Bertolotti Syndrome is, why it causes pain, how it's diagnosed, and the treatments available — including modern keyhole surgery.

Bertolotti Syndrome happens when a bony difference at the base of the spine — one that a person is born with — becomes a genuine source of lower back pain and, sometimes, leg pain.

The bony difference is called a lumbosacral transitional vertebra, often shortened to LSTV. In simple terms, the lowest vertebra in the lower back (usually the one called L5) has an enlarged wing of bone that either forms an extra "false joint" with the sacrum or pelvis, or fuses to it completely. This false joint is sometimes called a pseudoarticulation or pseudojoint.

The condition was first described by an Italian doctor, Mario Bertolotti, back in 1917. Even though it's been known for over a century, it remains one of the most commonly overlooked causes of back pain — especially in younger people.

An important point: having this bony variation on its own does not mean you have Bertolotti Syndrome. Many people have an LSTV and never feel a thing. The syndrome is only diagnosed when that false joint is confirmed to be the actual source of someone's pain.

The bony variation itself is surprisingly common — studies suggest somewhere between 3% and 36% of people have an LSTV, depending on the population studied. It appears to be more common in men than in women.

When it does cause symptoms, those symptoms often begin in early adulthood — frequently in a person's 20s or 30s. This is part of what makes it easy to miss: the pain shows up in younger patients who don't fit the usual pattern of age-related "wear and tear."

The pain doesn't come from a single source. Several things can contribute:

Extra strain on the segment above. The false joint makes the lowest level of the spine stiffer than normal. To make up for that lost movement, the level just above it has to work harder and move more. Over time, this can speed up wear in the disc and small joints at that level (often the L4–L5 segment).

A weaker supporting ligament. In many people with an LSTV, a key stabilising ligament just above the transitional area is naturally thinner and weaker. This can add to the instability and early disc problems at that level.

A pinched nerve ("Far-Out Syndrome"). The enlarged piece of bone can crowd the space where a major nerve (the L5 nerve root) exits the spine, pinching it in a hard-to-spot outer zone. This can cause pain, numbness, or tingling that travels into the hip or leg.

Arthritis in the false joint. Like any joint, the pseudoarticulation can develop arthritis, with inflammation and small changes in the bone, producing localised mechanical back pain.

Bertolotti Syndrome is frequently mistaken for more familiar problems, such as a slipped (herniated) disc or sacroiliac joint trouble, because the symptoms overlap. A few practical issues make it harder to detect:

It can hide on standard X-rays. An ordinary front-on X-ray often misses the LSTV. A special angled view called a Ferguson radiograph (taken at 30°) is the standard way to reveal it.

Counting the vertebrae gets tricky. Because the bottom of the spine is shaped differently, it can be hard to number the vertebrae correctly — which occasionally leads to treatment being aimed at the wrong level.

Getting to a confident diagnosis usually combines an examination with detailed imaging:

3D CT scans. These give the clearest picture of the bony variation and show exactly where a nerve might be pinched. They're considered the most accurate way to classify the type of LSTV.

A specialised bone scan (SPECT). This scan highlights areas of increased "stress" or activity, helping to tell an active, painful false joint apart from a harmless one that just happens to be there.

A diagnostic injection (the most reliable test). Under X-ray guidance, a local anaesthetic — often with a steroid — is injected directly into the false joint. If this brings significant relief (commonly around 80–100%), it confirms the joint is the true source of pain.

You may see terms like Castellvi or Jenkins in your scan report or hear them from your specialist. These are simply grading systems doctors use to describe the variation. The older Castellvi system focuses mainly on the size of the bony wing and whether it forms a joint or a full fusion. The newer Jenkins approach looks more at how close the bone sits to neighbouring structures, and it can identify some patients the older system misses. Your specialist can explain what your particular grade means for you.

Treatment almost always starts with the gentlest options and only escalates if needed.

The first approach is non-surgical and may include:

Physical therapy focused on core strength, stability, and stretching

Activity adjustments to avoid movements that flare the pain

Anti-inflammatory medication (NSAIDs)

Movement-based approaches such as Pilates or the Alexander technique, which some people find helpful for managing posture and muscle strain

If injections help but the relief is short-lived, radiofrequency ablation may be offered. RFA uses heat to quiet the small nerves supplying the false joint, often giving longer-lasting pain control without major surgery.

Surgery is considered only when conservative care hasn't worked. There are two main approaches, and the "best" choice is still debated among specialists:

Resection (transverse processectomy). The surgeon removes the painful enlarged bone and releases the false joint. This preserves movement in the spine.

Spinal fusion. The transitional segment is permanently joined to the sacrum to stop the movement that's causing pain.

How do the results compare? Both approaches tend to give good short-term relief. One comparative study (Mikula and colleagues, 2022) found that, over the longer term, fusion patients reported higher sustained pain improvement (78%) than those who had a simple resection (28%). However, fusion has its own trade-off: because it removes movement at that level, it can put extra stress on the discs above, which may wear out faster over time. Your surgeon will weigh these pros and cons with you based on your individual situation.

One of the most significant recent advances is full endoscopic resection — a keyhole technique that aims to deliver the benefits of removing the painful bone while keeping the surgery as small and gentle as possible.

In broad terms, the surgeon works through a very small incision (around 1 cm) using a thin tube fitted with a camera. Guided by live imaging, they carefully remove the enlarged bone and free the trapped nerve, while protecting the surrounding muscles and ligaments. Because the procedure is so targeted, it can often be done under local anaesthetic with sedation.

Why this matters for patients:

Often a day case. Many people are discharged within about 6 hours of surgery.

An added safety benefit. When the procedure is done under local anaesthetic, you can stay awake enough to give the surgeon feedback, which helps them protect the nerve during the operation.

Quick recovery. Most people return to unrestricted activity within around two weeks.

This motion-preserving approach is especially appealing for younger patients who'd prefer to avoid the long-term effects that can sometimes follow a spinal fusion.

No surgery is without risk, and keyhole resection requires careful, precise technique. Possible issues your surgeon will discuss include:

Temporary numbness or tingling. A sensitive bundle of nerve tissue near the surgical area can become irritated if handled too much, sometimes causing short-term altered sensation afterwards.

Nearby blood vessels. Important blood vessels sit close to the operating area, so surgeons use careful imaging and specialised instruments to maintain a safe working distance.

Fluid collection. Removing too much of the surrounding ligament can allow surgical fluid to track into nearby areas, which is why surgeons work efficiently to minimise this risk.

A specialist experienced in this procedure is best placed to talk you through how these risks apply to you.

Bertolotti Syndrome was once dismissed as a vague or "mythical" cause of back pain — but it's now recognised as a real, well-defined condition. With modern tools like 3D CT imaging, SPECT bone scans, and diagnostic injections, it can be diagnosed accurately and treated effectively.

For many people, non-surgical care or injections are enough. When surgery is needed, the keyhole (endoscopic) approach offers a compelling, ultra-minimally invasive option that targets the source of pain while preserving movement and allowing a fast recovery. If you think this condition might explain your back pain, a spine specialist can help you understand your options.

Important: This information is intended for general education only and is not a substitute for professional medical advice, diagnosis, or treatment. Always speak with a qualified healthcare professional about your symptoms and the options best suited to you. If you experience severe or worsening symptoms — such as significant leg weakness, numbness, or loss of bladder or bowel control — seek urgent medical attention.

• —NICE — Low Back Pain and Sciatica in Over 16s (NG59)
• —NHS — Spinal Conditions
• —British Association of Spine Surgeons (BASS)

This information is for general patient education and is not a substitute for an individual consultation. Always seek personalised advice from a qualified spinal specialist.