Prevalence and Biomechanics in Bertolotti Syndrome (BSy)
Understanding the Impact of Lumbosacral Transitional Vertebrae
Lumbosacral transitional vertebrae (LSTV) are among the most common congenital variations of the spine. Despite this, there is clinical significance that continues to be debated and, in many cases, overlooked.
Research suggests that LSTVs occur in approximately 4–36% of the population, although prevalence rates vary depending on the population studied and the classification system used. Most individuals with an LSTV will never develop symptoms. However, for some patients, the transitional anatomy may alter the biomechanics of the lumbosacral junction and contribute to the development of pain, a condition known as Bertolotti Syndrome (Bsy).
It is important to recognise that the presence of an LSTV alone does not constitute Bertolotti Syndrome (BSy). Rather that Bertolotti Syndrome (BSy) refers to a symptomatic transitional vertebra that has been identified as a pain generator or a contributing factor to a patient's symptoms.
A Congenital Condition Present From Birth
LSTVs develop during embryological formation of the spine and are present from birth. While symptoms may not appear until adolescence or adulthood, the anatomical variation itself is congenital.
One common misconception is that Bertolotti Syndrome (BSy) only affects older adults due to age-related degeneration. Current evidence demonstrates that this is not the case. Symptomatic Bertolotti Syndrome(BSy) has been reported in adolescents, young adults, athletes, and older individuals alike.
The age at which symptoms develop appears to be influenced by several factors, including the type of transitional vertebra, activity levels, occupational demands, genetic predisposition, joint mobility, and the cumulative effects of altered biomechanics over time. But for some individuals the symptoms have started in their younger years and have become more apparent in their adolescent years.
For some individuals, symptoms may emerge during periods of rapid growth, increased sporting activity, pregnancy, physically demanding employment, or following injury. Others may remain symptom-free for decades before degenerative changes around the transitional segment become clinically significant.
Biomechanics of Bertolotti Syndrome (BSy)
The lumbosacral junction serves as the transition point between the mobile lumbar spine and the relatively stable pelvis. This region plays a critical role in transferring forces generated during standing, walking, lifting, bending, and rotation.
In a typical spine, movement and load are distributed through the lumbar vertebrae, intervertebral discs, facet joints, sacrum, pelvis, and surrounding soft tissues in a coordinated manner. The presence of an LSTV can alter this relationship.
An enlarged transverse process may form a partial joint (pseudoarticulation) or complete fusion with the sacrum, ilium, or both. While this can create increased stability at the transitional level, it may simultaneously alter force transmission throughout the lumbosacral region.
Many studies suggest that reduced motion at the transitional segment may lead to increased mechanical stress and compensatory hypermobility at adjacent spinal levels. Over time, this altered load distribution may contribute to accelerated degeneration of the intervertebral discs, facet joints, ligaments, and surrounding soft tissues.
The biomechanical consequences are often compared to what occurs above a fused spinal segment. When movement is restricted at one level, neighbouring segments may be required to absorb greater forces and motion demands.
Potential Sources of Pain
Bertolotti Syndrome(BSy) should not be viewed as a single pain condition. Instead, it represents a spectrum of potential pain generators associated with transitional anatomy.
Pain may arise from:
The pseudoarticulation itself due to inflammation, arthritic change, or mechanical irritation.
Adjacent segment degeneration affecting the disc or facet joints above the transitional vertebra.
Nerve root irritation or compression resulting from altered anatomy or foraminal narrowing.
Contralateral facet joint overload, particularly in unilateral transitional vertebrae.
Secondary sacroiliac joint dysfunction resulting from altered pelvic mechanics.
Muscular compensation and chronic soft tissue overload.
Importantly, more than one pain generator may be present simultaneously.
Why Some Patients Develop Symptoms and Others Do Not
One of the greatest challenges in understanding Bertolotti Syndrome is explaining why some individuals remain asymptomatic while others develop significant pain and disability.
Current evidence suggests that symptoms are influenced by a combination of anatomical, biomechanical, and individual patient factors rather than the presence of a transitional vertebra alone.
Factors that may influence symptom development include:
The morphology of the transitional vertebra.
Unilateral versus bilateral involvement.
The degree of articulation or fusion.
Physical activity levels and occupational demands.
Adjacent segment degeneration.
Joint hypermobility or connective tissue disorders.
Individual variations in spinal and pelvic mechanics.
This variability highlights the importance of correlating imaging findings with clinical presentation.
Clinical Relevance
For healthcare professionals, the challenge lies not in identifying an LSTV on imaging, but in determining whether it is clinically relevant to the patient's symptoms and not to dismiss the findings based on old research.
For patients, it is important to understand that an LSTV is not automatically a source of pain. However, neither should it be dismissed solely because it is a common anatomical variant.
When symptoms, physical examination findings, imaging studies, and diagnostic investigations align, the transitional vertebra may represent a significant contributor to low back, sacroiliac, pelvic, groin, hip, or radicular pain.
As our understanding of Bertolotti Syndrome(Bsy) continues to evolve, increasing evidence supports the need for a comprehensive biomechanical assessment of the lumbosacral region rather than focusing solely on the transitional vertebra itself.
“A lumbosacral transitional vertebra is a congenital anatomical variation present from birth. While many individuals remain asymptomatic, altered biomechanics associated with the transitional segment may contribute to pain, degeneration, and functional impairment in a subset of patients. The challenge for Health Care Professionals is determining when the transitional anatomy is clinically relevant to the patient’s symptoms.”