Bertolotti syndrome is a cause of low back pain that stems from an anatomical quirk at the base of the spine: an unusually large or oddly shaped lowest lumbar vertebra that partially or fully fuses with the sacrum or pelvis. Named after Italian physician Mario Bertolotti, who first described the condition in 1917, it remains surprisingly underdiagnosed despite affecting a meaningful share of people with chronic low back pain. The condition sits in a frustrating gray zone where imaging can spot the abnormal anatomy easily enough, but proving that anatomy is actually the source of someone’s pain takes real detective work.
What Happens at the Base of the Spine
In a typical spine, the lowest lumbar vertebra (usually L5) sits above the sacrum with a clear separation. In people with a lumbosacral transitional vertebra, or LSTV, the transverse processes of that bottom vertebra are enlarged and reach toward the sacrum or the iliac bone of the pelvis. In mild cases, these bony wings are simply oversized. In more pronounced cases, the enlarged process forms a false joint (called a pseudoarticulation) with the sacrum. In the most extreme cases, the transverse process fuses completely with the sacrum, effectively turning the lowest lumbar vertebra into part of the sacral bone. This can happen on one side only or on both sides.
The classification system most commonly used, developed by Castellvi and colleagues in 1984, divides LSTVs into four types based on the severity and symmetry of the connection. Type I is simply an enlarged transverse process measuring at least 19 mm wide. Type II involves a pseudoarticulation, a partial bony bridge that forms a joint-like connection with the sacrum. Type III is complete bony fusion. Type IV is a mix, with a pseudoarticulation on one side and full fusion on the other. Each type can be unilateral (one side) or bilateral (both sides).1PubMed Central. Lumbosacral Transitional Vertebrae: Classification, Imaging Findings, and Clinical Relevance
Having this anatomy does not automatically mean you have Bertolotti syndrome. The transitional vertebra itself is just anatomy. Bertolotti syndrome is diagnosed only when the transitional vertebra is identified as the source of pain.2PubMed Central. A Comprehensive Update of the Treatment and Management of Bertolotti’s Syndrome: A Best Practices Review That distinction matters, because transitional vertebrae are far more common than the syndrome itself.
How Common Is It
Transitional vertebrae show up on imaging in somewhere between 4 and 36 percent of the general population, depending on the study and the criteria used. A large population-based study of nearly 6,000 people identified LSTVs in about 16 percent of subjects, with Type I (the mildest form, just an oversized transverse process) accounting for roughly 45 percent of those, and Type II (pseudoarticulation) making up about 43 percent. True bony fusion (Type III) and the mixed pattern (Type IV) were much less common, at around 7 and 5 percent of LSTV cases respectively.3PubMed. Lumbosacral transitional vertebra in a population-based study of 5860 individuals: prevalence and relationship to low back pain
Among people specifically presenting with low back pain, the picture shifts. A study at a major referral hospital in Uganda found that about 10 percent of patients seeking care for low back pain met criteria for Bertolotti syndrome, which the authors noted was higher than the globally reported prevalence of 5 to 7 percent in the general population.4PubMed Central. Prevalence, patterns, functional disability of Bertolotti syndrome among patients with low back pain at Mulago National Referral Hospital In that study, the median patient age was 49, roughly two-thirds were women, and over half had moderate disability as measured by standardized questionnaires. About 13 percent were categorized as crippled by pain.
Where the Pain Actually Comes From
The mechanics of pain in Bertolotti syndrome are more complex than “extra bone connection equals back pain.” Several distinct pain generators can be involved, sometimes simultaneously, which is part of why the condition is tricky to treat.
The pseudoarticulation itself is one source. When the enlarged transverse process forms a false joint with the sacrum, that joint can become inflamed and arthritic over time. Histologic analysis of surgically removed pseudoarticulations has shown tissue changes that look strikingly similar to what you find in osteoarthritic joints, suggesting the pseudoarticulation itself can degenerate and generate pain in the same way a worn-out knee or hip does.5PubMed. Histologic Assessment of Lumbosacral Transitional Vertebrae Pseudoarticulation as a Source of Pain in Bertolotti Syndrome
A second pain generator is the disc and facet joints at the level just above the transitional vertebra. Because the bottom segment is partially or fully anchored to the pelvis, the segment above it absorbs a disproportionate share of movement and stress. This concentrated mechanical load can accelerate disc degeneration and facet joint wear at that level, sometimes decades earlier than you would otherwise expect.6Spine. Bertolotti’s syndrome revisited: Transitional vertebrae of the lumbar spine In someone with a unilateral transitional vertebra (one side fused, the other side free), the asymmetry can overload the facet joint on the opposite side, causing pain that seems to have nothing to do with the abnormal anatomy.7Arquivos de Neuro-Psiquiatria. Transitional lumbosacral vertebrae and low back pain: diagnostic pitfalls and management of Bertolotti’s syndrome Pain on the “normal” side of a unilateral transitional vertebra is counterintuitive, and it can lead clinicians away from the real diagnosis.8PubMed. Partial lumbosacral transitional vertebra resection for contralateral facetogenic pain
A third mechanism involves nerve compression. The incomplete fusion and micromotion between the transverse process and the sacral wing can narrow the space where nerve roots exit the spine, leading to leg pain, numbness, or weakness. About 13 percent of patients with LSTVs have nerve root impingement, and up to 70 percent of those with impingement experience symptoms from it.9Journal of Minimally Invasive Spine Surgery and Technique. Surgical Options for Bertolotti Syndrome
The pain typically centers around the sacroiliac joint, groin, and hip region, which is another reason it gets missed. Many patients are initially worked up for hip pathology or sacroiliac joint dysfunction before anyone thinks to look closely at the bottom of the lumbar spine.
Why It Gets Misdiagnosed
Bertolotti syndrome has a reputation as an underdiagnosed condition, and that reputation is well earned. The first problem is recognition. Transitional vertebrae are often inaccurately detected and classified on standard X-rays and MRI, partly because these imaging studies frequently do not capture enough of the spine to correctly number the vertebrae.10PubMed Central. A Review of Symptomatic Lumbosacral Transitional Vertebrae: Bertolotti’s Syndrome Without knowing which vertebra is L5 and which is S1, a radiologist might mislabel the transitional level or miss it entirely.
The second problem is attribution. Even when a transitional vertebra is spotted on imaging, clinicians are often reluctant to blame it for the pain. Low back pain is extremely common, transitional vertebrae are common, and the two can coincide by chance. The “is this the problem, or did we just happen to find it?” question is legitimate. Confirming the diagnosis usually requires a diagnostic injection: a needle placed directly into the pseudoarticulation under fluoroscopic guidance, delivering local anesthetic and steroid. If the injection provides significant short-term pain relief, that is taken as evidence that the pseudoarticulation is actually generating the pain.11PubMed Central. Retrospective review of outcomes in patients with Bertolotti’s syndrome who underwent fluoroscopically-guided pseudojoint injections MRI can also help, with bone marrow edema (visible swelling in the bone near the pseudoarticulation) being a telling sign; mid-sagittal T2-weighted MRI has been reported to have about 80 percent sensitivity and specificity for the diagnosis when edema is present.12Journal of Surgical Case Reports. Bertolotti’s syndrome: an underdiagnosed cause for lower back pain
The Wrong-Level Surgery Problem
Beyond missed diagnoses, transitional vertebrae create a specific and dangerous practical problem: they confuse vertebral counting. When a surgeon looks at a preoperative MRI of the lumbar spine and sees five lumbar vertebrae, they assume a standard anatomy. But if the patient has a sacralized L5 (meaning L5 has partially fused to the sacrum and could be mistaken for part of the sacrum), the surgeon might count what is actually L4 as L5. The result can be wrong-level surgery, operating on the wrong disc or the wrong nerve root.13The Tohoku Journal of Experimental Medicine. Lumbosacral Transitional Vertebrae Cause Spinal Level Misconception in Surgeries for Degenerative Lumbar Spine Disorders
A systematic review on spinal level determination has emphasized that transitional vertebrae significantly complicate accurate level identification in both imaging and interventional procedures.14PubMed. Accuracy in spinal level determination, including transitional vertebrae: an ASReview supported systematic review This is not just a Bertolotti syndrome issue; anyone with a transitional vertebra undergoing lumbar spine surgery faces an elevated risk of level confusion, even if the transitional vertebra itself is not the reason for the surgery. Whole-spine imaging and careful preoperative counting using geometric landmarks on the sacrum are the standard safeguards.
Conservative and Interventional Treatment
Most patients with Bertolotti syndrome start with conservative treatment: activity modification to avoid positions and loads that aggravate the pain, over-the-counter or prescription pain medications, and physical therapy focused on core stability and flexibility. For many people, these measures are sufficient to manage symptoms, even if they do not resolve the underlying anatomical issue.
When conservative measures fall short, interventional options step in. Steroid and anesthetic injections directly into the pseudoarticulation, performed under fluoroscopic guidance, serve a dual purpose. They provide short-term pain relief for a subset of patients, and they help confirm the diagnosis. In one retrospective review, patients whose pseudojoint injections provided relief were also more likely to benefit from subsequent surgical resection, suggesting the injection has real diagnostic value even when its therapeutic benefit is temporary.15PubMed Central. Retrospective review of outcomes in patients with Bertolotti’s syndrome who underwent fluoroscopically-guided pseudojoint injections
Radiofrequency ablation (RFA) is another option that has gained traction. The idea is to use heat (or cold, or pulsed energy) delivered through a needle tip to disrupt the nerves carrying pain signals from the pseudoarticulation or the iliolumbar ligament. Several techniques have been described, including continuous, pulsed, cold, and bipolar RFA, as well as cryoablation targeting the iliolumbar ligament.16PubMed Central. A Comprehensive Update of the Treatment and Management of Bertolotti’s Syndrome: A Best Practices Review Some patients get months of relief from RFA, though the duration varies. One case report detailed a patient who got only brief relief from standard RFA of the iliolumbar ligament but responded much better to cryoablation targeting both ends of that ligament, suggesting that technique refinements can make a real difference for individual patients.17Indian Journal of Pain. Treatment of Bertolotti Syndrome: From Concept to Denervation
When Surgery Becomes the Answer
Surgery for Bertolotti syndrome generally comes into play after injections and ablation have confirmed the pain source but failed to deliver lasting relief. Two main surgical strategies exist, and the choice between them turns out to matter quite a bit for long-term outcomes.
The first approach is resection: surgically removing the enlarged transverse process and the pseudoarticulation, essentially disconnecting the abnormal bridge between the lumbar vertebra and the sacrum or pelvis. This can be done through minimally invasive techniques, including microendoscopic and fully endoscopic approaches, which have shown good results in individual cases and small series.18PubMed Central. Minimally Invasive Microendoscopic Resection of the Transverse Process for Treatment of Low Back Pain with Bertolotti’s Syndrome19Journal of Neurosurgery: Case Lessons. Minimally invasive full endoscopic resection of the anomalous transverse process in Bertolotti’s syndrome: illustrative case A larger series using minimally invasive tubular resection reported that the procedure was effective overall but noted several short-term complications.20PubMed. Minimally invasive tubular resection of the anomalous transverse process in patients with Bertolotti’s syndrome: presented at the 2013 Joint Spine Section Meeting
The second approach is fusion: rather than removing the bony bridge, the surgeon locks the transitional segment permanently in place using hardware, eliminating all motion at that level. This may sound counterintuitive (fusing what is already partially fused), but the goal is to stop the micromotion at the pseudoarticulation that drives inflammation and pain.
A comparative study looking at long-term pain improvement beyond 12 months found a substantial difference between the two approaches. Among patients who underwent fusion, about 78 percent reported lasting pain improvement. Among those who had the pseudoarticulation resected, only about 28 percent reported long-term improvement.21PubMed. Operative Treatment of Bertolotti Syndrome: Resection Versus Fusion That gap is striking and has shifted thinking in the field, though the numbers are still small and the ideal patient selection criteria remain a work in progress.
A more nuanced framework has been proposed that matches the surgical approach to the type of pathology. In one long-term outcomes study using a classification-based treatment algorithm, patients with isolated pseudoarticulation pain (Type 1 in that system) did well with resection alone, with 85 percent showing improvement. But patients who also had disc degeneration at the level above (Type 2) fared poorly with resection as a first step; 55 percent of those patients ultimately needed further procedures. Fusion worked better for that group, with 88 percent seeing some improvement. Patients with unilateral pathology (Type 4) did well with unilateral fusion, with 86 percent maintaining benefit at two years. Among all patients who had hip pain before surgery, 78 percent reported improvement in that hip pain after the operation.22PubMed. Redefining the Treatment of Lumbosacral Transitional Vertebrae for Bertolotti Syndrome: Long-Term Outcomes Utilizing the Jenkins Classification to Determine Treatment
Young Athletes and Adolescent Patients
Bertolotti syndrome is often framed as a middle-aged problem, but it can cause significant disability in teenagers and young adults. Because the transitional anatomy is present from birth (it is a developmental variant, not something acquired through injury), symptoms can emerge whenever the spine starts bearing serious load, which for athletes means adolescence.
One published case described a high school football player who had been dealing with worsening low back pain for a couple of years. The pain, centered on squatting and bending at the waist, eventually forced him to stop mid-practice and made climbing bleachers difficult.23PubMed Central. A Case Study of Bertolotti’s Syndrome in an Adolescent Patient Another case involved a 13-year-old who had been experiencing functional complaints for several years before receiving the correct diagnosis. After medical management provided only temporary relief, surgical resection of the enlarged transverse process was performed, and the child returned to full physical activity without pain or limitation.24PubMed. Bertolotti’s syndrome in children: From low-back pain to surgery. A case report
These cases highlight a practical concern: when a teenager complains of persistent back pain and standard evaluation shows nothing obviously wrong, transitional vertebrae should be on the differential. Young people with low back pain are often told they have a muscle strain and given generic advice. If the pain keeps coming back, particularly with loading activities, and standard imaging seems unremarkable, requesting full-spine films to count the vertebrae and check for transitional anatomy is a reasonable step.
An Old Debate That Refuses to Settle
More than a century after Mario Bertolotti published his original case in 1917, describing a patient whose low back pain was attributed to complete sacralization of L5, the fundamental question he raised still generates debate.25Interdisciplinary Neurosurgery. Bertolotti Syndrome: Does it really exist? systematic review Some researchers argue that the association between transitional vertebrae and low back pain is not as strong as Bertolotti suggested, pointing to population studies where many people with transitional anatomy have no symptoms at all. Others counter that the issue is not whether all transitional vertebrae hurt, but that some clearly do, and the challenge is reliably identifying which ones.
The current evidence leans toward a middle ground. Transitional vertebrae do predispose to certain patterns of degeneration and mechanical stress that can produce pain, but they are neither a guaranteed sentence to back problems nor an incidental finding to be dismissed. The strongest evidence for a real clinical syndrome comes from the diagnostic injection studies, where numbing the pseudoarticulation reliably reproduces and then abolishes the patient’s pain, and from the surgical literature showing meaningful improvement in selected patients. What the field still lacks is a large prospective trial that follows patients with LSTVs over many years to determine who develops symptoms, who does not, and what factors predict the difference.
Developmental Roots of Transitional Vertebrae
Lumbosacral transitional vertebrae are not injuries or consequences of aging. They are developmental variants, established before birth during the process that determines how many vertebrae end up in each spinal region. In embryonic development, the boundaries between the cervical, thoracic, lumbar, and sacral regions are set by patterning genes. When that patterning shifts, a vertebra that would normally be the last lumbar vertebra can take on sacral characteristics (sacralization), or the first sacral segment can take on lumbar traits (lumbarization). Research into vertebral patterning has found that in about 10 percent of people, the lumbosacral boundary shifts as part of broader homeotic transformations affecting multiple vertebral boundaries. Studies have also observed that the more boundaries are shifted, the more likely it is that other developmental variations are present elsewhere in the body.26SpringerLink / Evolutionary Biology. Evo-Devo of the Human Vertebral Column: On Homeotic Transformations, Pathologies and Prenatal Selection
For the average person with a transitional vertebra and back pain, this developmental backstory has limited practical relevance. But it does explain why some people have 4 mobile lumbar vertebrae and some have 6, and why counting vertebrae from the bottom up is inherently unreliable without imaging the full spine. It also explains why transitional vertebrae are not preventable, not caused by anything the patient did, and not something that can be “fixed” through exercise or posture correction. The anatomy is baked in from development; management is about addressing the mechanical consequences, not the root cause.