The phrase “5 lumbar type vertebral bodies” often appears in medical imaging reports, indicating a common anatomical variation in the lower back. This finding refers to a difference in the structure of the lumbosacral region, the junction between the lower spine and the pelvis. It suggests the person has five bones that structurally resemble the mobile bones of the lower back, deviating from the standard spinal configuration. Recognizing this variation is important for accurately interpreting imaging and planning potential procedures, though its presence alone does not automatically indicate pain or a medical problem.
Understanding Typical Spine Structure
The human spine is typically composed of 33 vertebrae, divided into five main sections. The lower back, or lumbar spine, normally contains five distinct, movable bones (L1 through L5). These lumbar vertebrae are characterized by large, kidney-shaped bodies and provide flexibility and support for the upper body’s weight.
Below the L5 vertebra lies the sacrum, a single bone formed from the fusion of five separate sacral vertebrae (S1 through S5). The sacrum is a fixed, triangular bone situated between the hip bones, acting as the foundation of the spine and transferring weight to the pelvis and legs. The standard configuration involves five mobile lumbar segments above this fused sacral base.
The mention of “5 lumbar type vertebral bodies” helps radiologists ensure correct segment counting. The standard spine has 24 presacral vertebrae (7 cervical, 12 thoracic, 5 lumbar) that are not fused to the sacrum. When a variation exists, the number of these mobile, lumbar-like segments may change, necessitating the specific count in the report.
Defining the Lumbosacral Transitional Vertebrae
The anatomical variation leading to a change in the number of lumbar-like bodies is known as a Lumbosacral Transitional Vertebra (LSTV). This congenital condition, present from birth, involves the lowest lumbar vertebra (L5) and the uppermost sacral segment (S1) showing features of the adjacent region. LSTVs are common, affecting an estimated 4% to 30% of the population.
The phrase “5 lumbar type vertebral bodies” often relates to LSTV, specifically sacralization or lumbarization. Sacralization occurs when the L5 vertebra partially or completely fuses with the sacrum, reducing the number of mobile lumbar segments to four. Conversely, lumbarization is when the first sacral segment (S1) separates from the sacrum, taking on the appearance of a sixth lumbar vertebra and resulting in six mobile lumbar bodies.
The transitional anatomy is categorized using the Castellvi classification system, which describes the degree of fusion or articulation.
Castellvi Classification System
- Type I involves an enlarged transverse process on the L5 vertebra without fusion.
- Type II involves a partial joint, or “pseudoarticulation,” between the L5 transverse process and the sacrum.
- Type III describes complete bony fusion between the transverse process and the sacrum.
- Type IV is a mix of a Type II on one side and a Type III on the other.
This classification helps medical professionals communicate the precise nature of the anatomical change.
Clinical Significance and Associated Symptoms
Having an LSTV is often an incidental finding, meaning the anatomical variation itself is frequently asymptomatic. Many people with this structural difference never experience related back pain. However, in a subset of people, the LSTV can cause chronic lower back pain, a condition specifically termed Bertolotti’s Syndrome.
Pain associated with Bertolotti’s Syndrome arises from the altered biomechanics of the spine caused by the LSTV. The partial fusion or articulation between the L5 vertebra and the sacrum reduces movement at the lowest spinal level. This reduction may place increased mechanical stress on the disc and joints immediately above the transition, typically the L4-L5 segment. Increased stress can lead to accelerated wear, degeneration, and possibly early disc herniation at the level above the LSTV.
Pain can also originate directly from the abnormal articulation, often called a pseudoarticulation, where the enlarged transverse process rubs against the ilium or sacrum. This repetitive rubbing causes inflammation and irritation, leading to localized pain in the lower back or buttock area. A diagnosis of Bertolotti’s Syndrome requires correlating the imaging finding of an LSTV with specific, chronic symptoms.