Sacralization of L5: A Congenital Condition
Yes, sacralization of L5 is a congenital condition that people are born with. Sacralization represents a transitional state at the lumbosacral junction that develops during embryonic development.
Embryological Development
- Sacralization of L5 occurs during early embryonic development, specifically during the period of neurulation in the second, third, and fourth weeks of human embryogenesis 1
- The caudal cell mass, which forms during secondary neurulation (beginning late in the fourth week), gives rise to the sacrococcygeal spine and related structures 1
- These developmental processes establish the vertebral structure before birth, including transitional vertebrae such as sacralized L5 1
Types of Sacralization
- Sacralization can be complete (bilateral complete fusion of L5 with the sacrum) or partial (unilateral fusion or accessory articulations) 2, 3
- Unilateral sacralization (Castellvi type IIIa variant) involves fusion of only one side of L5 to the sacrum 4
- Bilateral sacralization involves complete fusion of L5 to the first sacral segment 2
Prevalence and Recognition
- Lumbosacral transitional vertebrae (LSTV), including sacralization of L5, are relatively common congenital anomalies with an incidence of over 12% in the general population 5
- These transitional states are more susceptible to degenerative changes due to altered load-bearing patterns at the lumbosacral junction 2, 3
Morphological Characteristics
- Sacra with fused L5 vertebrae show distinct morphological features compared to normal sacra 2
- When L5 is sacralized, the auricular surfaces typically span from mid-L5 to mid-S2 segments 2
- Sacralization of L5 increases the sacral height, width, and auricular surface area 2
Clinical Significance
- Sacralization may be associated with low back pain in some individuals, though this relationship has been debated since it was first described by Bertolotti 5
- There appears to be a relationship with early disc degeneration above the transitional vertebra in younger patients 5
- Sacralization may represent a structural and biomechanical adjustment to compensate for reduced joint interfaces associated with smaller sacra 2
Diagnostic Considerations
- Radiographic imaging is the primary method for identifying sacralization 6
- MRI is the preferred imaging modality for evaluating transitional vertebrae and associated neural abnormalities 6
- Plain radiographs can identify vertebral fusion, spondylosis, malalignment, or spinal canal stenosis associated with sacralization 6
Associated Conditions
- Sacralization may be associated with other congenital anomalies of the spine 6
- It's important to recognize that sacralization is distinct from coccygeal dimples, which are benign variations that typically require no intervention 7
Sacralization of L5 represents one end of a transitional "spectrum," with lumbarization of the S1 sacral segment representing the other end 2. Understanding these congenital variations is important for proper diagnosis and management of related spinal conditions.