A transitional vertebra is a spinal bone at the border between two sections of the spine that looks partly like each, and you are born with it. It is usually found by chance on an X-ray or MRI done for something else, and most people with one never have symptoms.1PubMed Central. Septic Arthritis: A Very Uncommon but Remarkable Complication Revealing Bertolotti Syndrome in a Child It still matters in two ways: some forms add strain that can lead to pain, and it can throw off how doctors count your vertebrae.
What Your Scan Report Means
Most people have 5 lumbar vertebrae in the lower back, sitting on the sacrum, a triangle-shaped bone made of fused vertebrae. The most common transition happens at that junction, and reports call it a lumbosacral transitional vertebra, or LSTV. Transitions can also happen higher up, where the rib-bearing upper spine meets the lower back, and at the base of the neck.
The variation goes in two directions. In sacralization, the lowest lumbar vertebra has partly joined the sacrum, so the lower back acts as if it has 4 movable vertebrae. In lumbarization, the top piece of the sacrum has separated and behaves like a sixth lumbar vertebra. The hallmark is an enlarged side wing of the lowest vertebra that touches, forms a joint with, or fuses to the sacrum or pelvis.2PubMed Central. Septic Arthritis: A Very Uncommon but Remarkable Complication Revealing Bertolotti Syndrome in a Child It forms before birth, when genes that set each vertebra’s identity draw the borders between spine regions slightly off.3PubMed Central. Hox genes specify vertebral types in the presomitic mesoderm
The total number of vertebrae stays the same; what changes is where the movable section ends and the fixed base begins. Which direction you have depends on how the radiologist counts, so the same bone may be called sacralization on one report and described differently on another.
Every lumbar vertebra has small bony wings sticking out to each side. In a transitional vertebra the lowest pair is wider and more block-shaped, often described as triangular or like a pelvic wing. It can be enlarged on one side or both, so a report may say left, right, or bilateral, and the two sides can even differ in type.
On a real report, you may see phrases like “transitional lumbosacral anatomy,” “six lumbar-type vertebrae,” or “partial sacralization of L5.” These words describe shape, not a disease or injury. The bone shape itself is fixed and does not change with age. Finding one does not mean surgery or restrictions, and treatment is only considered if pain clearly comes from it. A useful question for your doctor is which vertebra the report labeled as L5, and why.
How Common Transitional Vertebrae Are
Across many studies, about 15% of people have a lower-back transitional vertebra, roughly 1 in 7.4PubMed Central. Prevalence, diagnosis, and clinical significance of lumbosacral transitional vertebrae: A systematic review and narrative analysis Individual studies range from about 4.5% to 36%.5PubMed Central. Prevalence, diagnosis, and clinical significance of lumbosacral transitional vertebrae: A systematic review and narrative analysis In adults scanned for back symptoms, about 19% had one, mostly sacralization rather than lumbarization.6Surgeries. Prevalence of Lumbosacral Transition Vertebrae in Symptomatic Adults and the Levels of Degeneration in the Suprajacent Disc A transition at the upper-back-to-lower-back border shows up in about 11% of CT scans.7Journal of Orthopaedic Reports. Prevalence, types and radiological features of thoracolumbar transitional vertebra – a CT based cross sectional study
The spread comes from who was scanned and how the variation was defined. Studies that scan only people with back pain, or only people having CT for abdominal problems, draw from different groups, so their rates are not directly comparable. Some count only fused or jointed types, while others also count a merely enlarged side wing, which pushes the percentage up. Imaging matters too, since a CT shows bone detail better than a basic X-ray and can reveal more cases. Because it is so common, many people with no back pain carry one without knowing, so it should not be blamed automatically for pain.
Transitions also tend to come together. People with a transition higher in the spine are about 7 times more likely to also have one at the lower back.8PubMed Central. The prevalence and clinical significance of transitional vertebrae: a radiologic investigation using whole spine spiral three-dimensional computed tomographic images
Can It Cause Back Pain
Doctors grade these with the Castellvi types I to IV, which may appear on your report. Type I is just an enlarged side wing. Type II forms a false joint with the sacrum. Type III is solidly fused. Type IV mixes a joint on one side with fusion on the other. Type II is the most common kind found.9Translational Research in Anatomy. Lumbosacral transitional vertebrae of 3096 individuals: Prevalence and morphology in a South African population and its association with population affinity
Each type also has an “a” and “b” form, meaning one side or both sides, so a report that says type IIb describes a false joint on both sides. Type I is so common and mild that it is generally treated as an ordinary variation rather than a cause of pain.
The type matters more than the mere presence of the variation. About 54% of people without a transitional vertebra reported low back pain.10PubMed Central. Lumbosacral transitional vertebrae: association with low back pain Among people with type II it was 73%, and with type IV 66%.11PubMed Central. Lumbosacral transitional vertebrae: association with low back pain Type I and type III were at 46% and 40%, no higher than people without one.12PubMed Central. Lumbosacral transitional vertebrae: association with low back pain
The reason lies in what a false joint is: a spot where two bones that normally stay apart touch and rub, with a thin coating of cartilage-like tissue and a joint capsule that can become irritated. Under load, that contact can wear and become inflamed, while solid fusion does not move.13PubMed Central. Septic Arthritis: A Very Uncommon but Remarkable Complication Revealing Bertolotti Syndrome in a Child
People often point to one side of the low back just beside the spine, close to the top of the buttock, rather than the center. The ache can seem to travel into the hip, groin, or the dimple area over the pelvis, which is why it is sometimes mistaken for a hip or sacroiliac problem. It tends to be worse with standing, bending, or lifting and eases with rest or a change in position, which marks it as mechanical rather than constant.
Even a type II or IV finding is not proof. Other common causes like disc or joint problems still need checking. One way doctors check the link is by testing whether numbing the false joint relieves the pain.
Bertolotti Syndrome and Pinched Nerves
Bertolotti syndrome is the name for chronic back pain caused by a transitional vertebra.14PubMed Central. A Comprehensive Update of the Treatment and Management of Bertolotti’s Syndrome: A Best Practices Review It is especially noted in teenagers and young adults.15PubMed Central. Septic Arthritis: A Very Uncommon but Remarkable Complication Revealing Bertolotti Syndrome in a Child Some experts argue it is less a separate disease than a change in spine mechanics that sets up other familiar painful problems.16Interdisciplinary Neurosurgery. Bertolotti Syndrome: Does it really exist? systematic review
The bone can also trap a nerve. A spinal nerve can get pinched between the enlarged side wing and the sacrum.17International Journal of Spine Surgery. What Are Transitional Vertebrae and Why Do They Matter? This can feel like sciatica, pain shooting down one leg. In one reported case, removing the excess bone fully relieved the man’s back and leg pain.18PubMed Central. A case of Bertolotti’s syndrome as a cause of sciatica
Treatment usually starts gently. Physical therapy focuses on strengthening the muscles around the trunk and hips and improving flexibility, so less stress lands on the false joint. Activity changes mean temporarily cutting back on movements that reliably provoke pain, such as repeated arching or heavy lifting, rather than stopping everything. Anti-inflammatory medicine can calm irritation in the joint, though it is a short-term aid for flares rather than a cure.
An injection can both diagnose and treat. A doctor guides a needle into the false joint using X-ray or CT and delivers numbing medicine, often with a steroid. If pain relief appears within a short time, the joint is the likely source, and the steroid may extend relief for weeks or longer. If it does not help, the doctor has learned something valuable before any surgical decision.
Surgery, removing or fusing the false joint, is reserved for stubborn pain. Before it, ask whether a diagnostic injection has confirmed the joint as the pain source.
Tell your doctor about leg pain, numbness, or tingling that follows a nerve path, and one-sided pain that worsens with twisting or bending. Weakness in a leg needs prompt evaluation.
Extra Wear on the Disc Above
When the lowest level moves less, the level above moves more to compensate.19Orthopaedic Practice. Management of Transitional Vertebra in An Amateur Level Teenager Circus Acrobat: A Case Report Stress concentrates on the disc above the transitional vertebra.20PubMed Central. Biomechanical influence of numerical variants of lumbosacral transitional vertebra with Castellvi type I on adjacent discs and facet joints based on 3D finite element analysis Discs are cushions that wear gradually with repeated stress, so a level doing more than its share tends to dry out and thin earlier. People with Bertolotti syndrome had about 2.7 times the odds of significant wear on that disc above.21PubMed. Examining degenerative disease adjacent to lumbosacral transitional vertebrae: a retrospective cohort study
The ligament steadying that upper level tends to be thinner and weaker.22PubMed Central. Investigating biomechanical differences in lumbosacral transitional vertebrae among different Castellvi classifications That ligament runs from the pelvis to the vertebra above and helps hold it steady, so a thinner one leaves it less supported against sliding and twisting. Combined with extra motion, this helps explain why the disc above is the common site of trouble.
The disc below a fully fused vertebra tends to wear less than usual.23PubMed Central. Investigating biomechanical differences in lumbosacral transitional vertebrae among different Castellvi classifications Less wear below does not cancel the extra strain above. On a scan, disc wear above the transitional vertebra is common and does not automatically mean it is the source of pain.
For active people, sports with repeated bending, arching, twisting, or landing put more strain on the overworked level. Pain in young athletes often flares during intense workouts or direction changes. Core strengthening is commonly used to help share the load.
Why Counting Your Vertebrae Gets Tricky
With an extra or missing lumbar-type vertebra, the bone labeled L5 on one scan may be called L4 or S1 on another.24PubMed. Accuracy in spinal level determination, including transitional vertebrae: an ASReview supported systematic review Radiologists usually label vertebrae by counting from a landmark, and different landmarks give different answers in this situation. A lower-back-only image may not show enough of the spine to count from the top, so the reader must guess where to start.
Wrong-level spine operations have been traced to this kind of numbering mistake.25The Tohoku Journal of Experimental Medicine. Lumbosacral Transitional Vertebrae Cause Spinal Level Misconception in Surgeries for Degenerative Lumbar Spine Disorders In one review of 42 people with transitional vertebrae, 5 had surgery at the wrong level due to naming errors.26PubMed Central. Anatomical Variations That Can Lead to Spine Surgery at the Wrong Level: Part III Lumbosacral Spine An injection or operation is aimed at a specific vertebra, so being off by one means treating a healthy level while leaving the painful one alone.
Counting down from the second neck vertebra on images of the whole spine is the most reliable method.27American Journal of Neuroradiology. Lumbosacral Transitional Vertebrae: Classification, Imaging Findings, and Clinical Relevance Doctors may also use a ligament that attaches to L5 as a landmark, though it assumes a typical number of vertebrae.28American Journal of Neuroradiology. Lumbosacral Transitional Vertebrae: Classification, Imaging Findings, and Clinical Relevance A standard lower-back X-ray mislabeled the type of transitional vertebra in about 35% of cases compared with CT.29PubMed Central. Lumbar plain radiograph is not reliable to identify lumbosacral transitional vertebra types according to Castellvi classification principle
If two reports disagree, it usually reflects one radiologist counting from the top and another from the bottom, not a change in your spine. A whole-spine image can settle which label is correct.
Before any spine procedure, tell every new doctor, surgeon, or pain specialist that you have a transitional vertebra. Bring earlier scans so everyone uses the same numbering, and ask how the level will be confirmed during the procedure. Make sure the reports and the operative plan name the same vertebra.
Transitional Vertebrae Elsewhere in the Spine
The most common higher transition is a missing or very short 12th rib.30Journal of Orthopaedic Reports. Prevalence, types and radiological features of thoracolumbar transitional vertebra – a CT based cross sectional study Most people have 12 pairs of ribs, and the lowest pair can be short or absent without affecting breathing or health. Because the 12th rib normally helps identify the last chest vertebra, its absence changes which bone looks like the first lumbar vertebra and adds to counting errors. People with an unusual rib count are far more likely to have a transition at this border.31PubMed Central. The prevalence and clinical significance of transitional vertebrae: a radiologic investigation using whole spine spiral three-dimensional computed tomographic images
That is why rib counts show up on your report. Ribs are a visible clue to where the chest spine ends and the lower back begins, so radiologists note them to number vertebrae correctly. An absent 12th rib alone rarely causes symptoms, and mentioning it is usually a labeling aid, not a warning.
At the other end, a cervical rib is an extra small rib at the base of the neck. It grows from the lowest neck vertebra and can be a complete rib or only a small bony or fibrous band. It can compress nerves and blood vessels heading to the arm.32Journal of Medical Cases. Neurogenic Thoracic Outlet Syndrome: Causing by Cervical Rib That can cause arm numbness, tingling, or weakness, a rare condition called thoracic outlet syndrome.33Journal of Medical Cases. Neurogenic Thoracic Outlet Syndrome: Causing by Cervical Rib Many people with one never know it is there, because it only matters when it crowds the space that nerves and vessels pass through. Arm symptoms with a neck rib deserve a doctor visit.
Living With a Transitional Vertebra
Most people never need treatment for it.34PubMed Central. Septic Arthritis: A Very Uncommon but Remarkable Complication Revealing Bertolotti Syndrome in a Child Exercise and sports are generally fine as long as they don’t hurt. Keeping a copy of the report that names the variation lets future doctors see the wording and numbering used, so they don’t have to guess, and it can avoid repeat imaging just to clarify the level.
On PET scans used to follow cancer, a transitional vertebra can rarely light up and be mistaken for disease.35Indian Journal of Nuclear Medicine. Incidental 18F-FDG Uptake in a Lumbosacral Transitional Vertebra: A Rare Pitfall On 18F-FDG PET/CT During Oncologic Response Assessment A PET scan highlights tissue that is using extra sugar, and an irritated joint can take up more, looking like a tiny abnormal spot. The radiologist can often tell the difference using a CT done at the same time, but if you have cancer imaging, mention the variation so it isn’t misread.