Bertolotti's Syndrome (BSy) represents a complex and often underdiagnosed cause of chronic low back pain, originating from a congenital anomaly at the lumbosacral junction. First described in 1917 by Italian surgeon Mario Bertolotti, the syndrome establishes a clinical link between a specific anatomical variant called the lumbosacral transitional vertebra (LSTV) and the experience of pain (Alonzo et al., 2018). Several studies have tried to ascertain the incidence rate for LSTV in the general population. However, there is a large variance where between 4-36% of people included in their studies have LSTV (Crane et al., 2021; Hsieh et al., 2000). The most accurate figure on the incidence of LSTV in the general population was found to be close to 20% after analysis of radiological images of 6200 individuals (Uçar et al., 2013). Given the presence of LSTV in nearly 1 in 5 people, we do not observe a similar number of people diagnosed with Bertolotti’s Syndrome.
The presence of LSTV is an anatomical observation. Bertolotti's Syndrome, however, is a clinical diagnosis made only when this LSTV is definitively identified as the source of a patient's chronic low back pain and associated symptoms (Crane et al., 2021).
This distinction is of paramount clinical importance because a significant portion of individuals with LSTV remain entirely asymptomatic throughout their lives. The challenge for clinicians, therefore, is not merely to identify the LSTV on an imaging study but to rigorously prove its causal relationship to the patient's pain, a process that often requires a combination of detailed imaging and diagnostic injections (Alonzo et al., 2018). This diagnostic hurdle is a primary reason why the condition is frequently overlooked, leading to prolonged periods of patient suffering and ineffective treatments directed at other potential pain sources.
The presence of LSTV fundamentally alters the biomechanics of the lumbosacral spine initiating a cascade of pathological changes that can lead to pain. In a normal spine, forces are distributed through the mobile lumbar segments to the stable sacropelvic complex. However, an LSTV introduces hypomobile lumbar segment results in hypermobility and greater forces applied on the segment immediately above (Alonzo et al., 2018).
The altered biomechanics can result in patients presenting with lower back pain. The source of this pain can be attributed to various factors stemming from the changes caused by the LSTV. Some of these sources of pain include:
Direct effects of LSTV
Arthritis of the pseudo-articulation
In LSTV types where the transverse process forms a “false joint” with the sacrum (i.e., type II & type IV), the bone-on-bone contact leads to mechanical grinding, inflammation, and the formation of osteophytes. This can lead to direct localized, aching pain (Poe, 2013).
Radiculopathy
Radiculopathy (i.e., pain radiating down the leg) can occur through several mechanisms. This can be caused by direct compression of the exiting L5 nerve root due to the enlarged transverse process. Alternatively, the local inflammation caused by osteophyte formation due to pseudo-articulation can lead to irritation of the exiting L5 nerve root. Alternatively, the hypermobility at the L4-L5 level due to LSTV can cause disc herniation at L4 or L5 (Jancuska et al., 2015).
Secondary effects of LSTV
Myofascial pain
The body’s attempt to stabilize the anomalous anatomy can cause increased strain on the musculature around the LSTV. This can lead to hypertonicity in the Quadratus Lumborum (QL) and the Iliopsoas that can cause formation of chronic strain and trigger points in these muscles (Jain et al., 2013).
Contralateral facet joint stress
The asymmetrical motion caused by unilateral LSTV can place excessive load on the facet joint on the opposite side of the pseudo-articulation. This can lead to facet joint pain and development of arthritis (Jancuska et al., 2015).
Adjacent segment disease
Compensatory hypermobility of the segment above the LSTV can lead to acceleration of degeneration of the disc. This, in turn, leads to higher incidence of disc herniation, annular tears (i.e., tear of the outer wall of the disc), and spinal stenosis compared to individuals with normal anatomy (Crane et al., 2021).
