Bertolotti syndrome is a congenital spinal condition where an abnormal connection between the lowest lumbar vertebra (L5) and the sacrum causes chronic low back pain. It’s more common than many people realize: lumbosacral transitional vertebrae, the structural anomaly behind the syndrome, are present in an estimated 10% to 20% of the general population, with one study finding them in nearly 27% of participants. Not everyone with the anomaly develops pain, but for those who do, it can be a frustrating diagnosis to reach because the symptoms overlap with so many other causes of back pain.
What Happens in Your Spine
Your lumbar spine normally ends at the L5 vertebra, which sits on top of the sacrum, the triangular bone at the base of the spine. On each side of every vertebra, small wing-like projections called transverse processes stick out to the left and right. In Bertolotti syndrome, one or both of the L5 transverse processes are abnormally enlarged and form a connection with the sacrum or the top of the pelvis (the ilium) that isn’t supposed to be there.
This extra connection can take several forms. Sometimes the enlarged transverse process simply touches or loosely articulates with the sacrum, creating what’s called a pseudoarticulation. In other cases, it fuses completely to the sacrum with solid bone. The connection can happen on one side or both. Because the L5 transverse processes need to bear load across the sacral surface in this arrangement, they grow larger than those found in people without the anomaly.
Clinicians use the Castellvi classification to describe the severity:
- Type I: One or both transverse processes are enlarged (at least 19 mm wide) but haven’t formed a joint or fused to the sacrum.
- Type II: An enlarged transverse process on one or both sides forms an incomplete, movable joint with the sacrum.
- Type III: One or both transverse processes have fully fused to the sacrum with solid bone.
- Type IV: A combination, with an incomplete joint on one side and complete fusion on the other.
Understanding which type you have matters because it influences both how the pain behaves and which treatments are most appropriate.
Why It Causes Pain
The extra connection between L5 and the sacrum effectively immobilizes or restricts movement at the bottom of your spine. Your body compensates by placing more stress on the segment directly above, the L4-L5 disc and facet joints. Over time, this leads to what’s known as adjacent segment degeneration: the disc at L4-L5 wears out faster, the facet joints become arthritic, and in some cases the vertebra can slip forward (spondylolisthesis).
Patients with Bertolotti syndrome tend to have a higher pelvic incidence, a measurement of pelvic alignment that, when mismatched with the curve of the lower back, increases the loads and shear forces on the intervertebral discs. So the structural anomaly doesn’t just create a stiff segment at L5-S1. It reshapes the biomechanics of the entire lower spine, accelerating wear at the levels above. The pseudoarticulation itself can also become a direct source of pain, especially in Type II cases where the movable joint becomes inflamed.
Symptoms and Who Gets Them
The hallmark symptom is low back pain, typically centered around the lower lumbar region and sometimes radiating into the buttock or hip on the affected side. When adjacent segment degeneration progresses far enough, you can develop nerve-related symptoms like shooting leg pain (radiculopathy) or difficulty walking due to spinal canal narrowing (neurogenic claudication).
Because you’re born with the anomaly, symptoms can begin surprisingly early compared to typical degenerative back conditions. Many patients first notice pain in their 20s or 30s, which is one reason Bertolotti syndrome is described as an important cause of low back pain in young adults. The pain often worsens with prolonged standing, bending, or twisting and may improve with rest.
How It’s Diagnosed
Standard X-rays of the lumbar spine can reveal an enlarged transverse process, but Bertolotti syndrome is easy to miss on routine imaging if the radiologist isn’t looking for it. A Ferguson view, which is an angled X-ray taken with the beam tilted 30 degrees upward toward the head, offers slightly higher sensitivity for spotting the abnormal connection than a standard front-to-back view. MRI and CT scans provide additional detail, showing the condition of the pseudoarticulation, the adjacent discs, and any nerve compression.
One of the trickiest aspects of diagnosis is confirming that the transitional vertebra is actually the source of your pain, rather than an incidental finding. A diagnostic injection of local anesthetic into the pseudoarticulation can help. If the injection temporarily eliminates your pain, it strongly supports Bertolotti syndrome as the culprit.
Conservative Treatment Options
Most people start with non-surgical management, and many get meaningful relief. The first line is usually a combination of activity modification, over-the-counter pain relief, and physical therapy. Physical therapy focuses on improving mobility in the lower back and strengthening the core muscles that support the spine. Case reports have documented noticeable improvements in pain and mobility within two to four weeks of manual therapy and targeted exercises. Pilates-based programs may also offer short-term benefits for the kind of chronic low back pain associated with this condition.
When physical therapy alone isn’t enough, injections can help. Steroid and anesthetic injections directly into the pseudoarticulation have shown strong results. In one cohort, 8 out of 10 patients experienced complete pain relief within 30 minutes of injection, with the duration of relief ranging from a single day to over 27 months. Epidural steroid injections at the level of the transitional vertebra can also help, particularly when nerve root irritation is part of the picture.
Radiofrequency ablation (RFA) is another option that has gained traction. This procedure uses heat to disrupt the pain-signaling nerves around the pseudoarticulation. Several forms exist, including continuous, pulsed, and bipolar techniques. In one notable case, a patient who had failed other treatments underwent bipolar RFA with targeted lesioning around the abnormal joint and remained completely pain-free through 16 months of follow-up.
When Surgery Is Considered
Surgery is typically reserved for patients who don’t respond to conservative treatment or who have developed significant adjacent segment problems. The two main surgical approaches are resection of the enlarged transverse process and spinal fusion.
Resection involves surgically removing the abnormal bony connection, freeing the L5 vertebra from the sacrum. This can work well when the pseudoarticulation itself is the primary pain source and the rest of the spine is relatively healthy. Fusion, on the other hand, is more appropriate when adjacent segment degeneration has progressed to the point of disc collapse, spondylolisthesis, or severe facet arthropathy at L4-L5. In these cases, a one-level or even two-level fusion may be needed to stabilize the affected segments and decompress any pinched nerves.
Choosing between the two depends on where your pain is coming from and how much structural damage has accumulated. If the disc above the transitional vertebra is still in reasonable shape, resection alone may be sufficient. If L4-L5 has already degenerated significantly, fusion at that level, sometimes extending to include the transitional segment, becomes the more reliable option.
Living With the Diagnosis
Bertolotti syndrome is frequently underdiagnosed, partly because many clinicians don’t routinely look for transitional vertebrae on imaging and partly because the symptoms mimic so many other back conditions. If you’ve been dealing with persistent low back pain that started at a younger age than expected and hasn’t responded well to standard treatments, it’s worth asking whether imaging has specifically evaluated for a lumbosacral transitional vertebra.
The good news is that the condition has a clear structural cause, which means treatments can be precisely targeted. Between physical therapy, injections, ablation procedures, and surgery when necessary, most patients can find a combination that brings their pain to a manageable level or eliminates it entirely.