Back pain is a common experience. While muscle strain and degenerative changes are frequent causes, sometimes the pain originates from an anatomical difference present since birth. This variation, often referred to as an “extra vertebra,” can be an overlooked source of chronic lower back discomfort. Although many people with this spinal configuration remain free of symptoms, for others, it creates a biomechanical imbalance that leads to significant pain.
What Is a Transitional Vertebra?
The term “extra vertebra” commonly refers to a Lumbosacral Transitional Vertebra (LSTV), a congenital anomaly at the junction between the lower back and the pelvis. This variation occurs when the spine’s lowest segments take on characteristics of their neighbors, altering the standard five lumbar vertebrae count. The two main forms are sacralization and lumbarization, both of which alter the normal mechanics of the lumbosacral region.
Sacralization is the more common type, involving the fifth lumbar vertebra (L5) partially or completely fusing to the sacrum, the triangular bone at the base of the spine. Lumbarization, conversely, is where the first segment of the sacrum (S1) separates and takes on the features of a lumbar vertebra, creating six lumbar-like segments. This structural difference is relatively frequent, appearing in an estimated 4% to 35.6% of the general population.
These transitional segments often feature enlarged transverse processes, which are bony projections extending sideways from the vertebra. These enlarged processes may partially or fully join the sacrum or the ilium (pelvic bone), leading to an abnormal bony connection. While this anatomical finding is common, it only becomes a condition, known as Bertolotti Syndrome, when it is the definitive source of a person’s low back pain.
How This Variation Causes Back Pain
The pain associated with a transitional vertebra stems from the abnormal articulation that forms between the enlarged transverse process and the sacrum or ilium. This connection is called a pseudoarthrosis, essentially a “false joint” that lacks the smooth cartilage and structure of a healthy joint. Movement in the lower back causes repetitive friction and irritation at this pseudoarthrosis, leading to localized inflammation and chronic pain.
This altered anatomy disrupts the normal distribution of mechanical stress across the lower spine. The transitional segment acts as a stiff anchor, severely limiting motion at the lumbosacral junction. The compensatory movement is then shifted to the spinal segment immediately above the LSTV, typically the L4-L5 disc.
This increased stress can cause accelerated degeneration, leading to disc herniation or facet joint arthritis at the level above the LSTV at a younger age. The enlarged transverse process can also be a direct source of pain by physically compressing the exiting L5 spinal nerve root, sometimes referred to as “Far-Out Syndrome.” This compression produces radicular pain, which radiates down into the hip or leg.
Identifying the Source of Pain
The presence of a transitional vertebra on imaging does not automatically mean it is the cause of a patient’s back pain, making accurate diagnosis complex. The initial step involves imaging studies, typically X-rays of the lumbar spine and pelvis, to visualize the bony structure and classify the LSTV type. Specialized views, such as the Ferguson projection, are often used to highlight the lumbosacral junction.
A computed tomography (CT) scan offers detailed visualization of the pseudoarthrosis and surrounding bone structures. Magnetic resonance imaging (MRI) is used to evaluate soft tissues, including the discs and nerves. Imaging is also used to rule out other common causes of back pain, such as disc herniation or facet arthrosis.
The definitive method for linking the anatomical finding to the patient’s symptoms is a diagnostic anesthetic injection. This procedure involves injecting a local anesthetic, often combined with a steroid, directly into the pseudoarthrosis joint. If the patient experiences temporary, significant relief immediately following the injection, it confirms the transitional vertebra as the primary pain generator.
Treatment Options for Symptomatic Transitional Vertebrae
Initial management for symptomatic transitional vertebrae typically follows a conservative pathway focused on reducing inflammation and stabilizing the spine. Physical therapy is instrumental, concentrating on core strengthening and lumbar stabilization exercises to improve biomechanics and reduce stress on the affected segment. Anti-inflammatory medications are frequently used to manage the localized pain and irritation originating from the pseudoarthrosis.
If conservative measures do not provide adequate relief, targeted interventional procedures become the next option. Targeted injections of local anesthetic and corticosteroids directly into the painful pseudoarthrosis can offer longer-lasting relief by calming the joint’s inflammation. For some patients, radiofrequency ablation (RFA) around the transitional segment may be considered to interrupt the pain signals from the irritated nerves.
Surgical intervention is reserved for individuals with persistent pain who have failed to respond to extensive non-surgical treatment. The most common surgical approach is pseudoarthrectomy, which involves surgically resecting, or removing, the problematic bony articulation of the enlarged transverse process. This procedure aims to eliminate the source of the mechanical friction and inflammation. In rare cases involving significant instability or failure of resection, spinal fusion may be performed to permanently stabilize the lumbosacral segment.