What is Bertolotti’s Syndrome?

Bertolotti’s Syndrome (BS) is pathology caused by a congenital deformity of the spine that results in lumbosacral transitional vertebrae (LSTV). This, in simple terms, can mean the following:

The last segment (vertebra) of the lumbar spine (typically L5) is partially or completely sacralized: L5 has overgrown transverse processes that have formed either a pseudo-articulation (i.e., false joint) or partially fused to the sacral ala on one or both sides.
The first segment of the sacrum (S1) is partially lumbarized: S1 has not completely fused with the rest of a sacrum. Instead, it looks like a lumbar segment. It is characterized by overgrown transverse processes that form pseudo-articualtion with the sacral ala.

In some cases, the transverse processes would fully fuse with the sacrum at one or both sides leading to a fully sacralized lumbar segment (McGrath et al., 2021; Zhu et al., 2023). This is further elucidated in the “What is the Castellvi classification of LSTV” Section.

It is important to note that the presence of the lumbosacral transitional anatomy (LSTV) does not mean it is the primary pain generator. Research has shown that LSTV has been observed in 4-30% of the general population (Alonzo et al., 2018). This, coupled with the fact that only incidence of Bertolotti’s Syndrome (BS) is 4-8% in patients with lower back pain, can lead to dismissing LSTV as an incidental finding on patients’ imaging (Kapetanakis et al., 2017).

Overview of spinal anatomy

Please use the following videos to better understand the terminology used to describe the different types of LSTV and spine anatomy as a whole. You can also find further reading here: https://spinehealth.org/article/spine-anatomy/

Overview of lumbar spine anatomy

Overview of sacral anatomy

What is Castellvi classification of BS?

Original classification by Dr. Antonio Castellvi

The modern classification of LSTV anatomy was introduced by Castellvi et al in 1984 to characterize the different types of transitional anatomy observed in patients (Castellvi et al., 1984). There are 4 broad categories of LSTV:

Modified classification by Dr. Arthur Jenkins

Dr. Jenkins and his team performed a retrospective cohort study of 150 patients to revise the Castellvi classification. Based on the teams findings, this revised classification better describes functional anatomy, identify uncaptured anatomy (namely, type I anatomy) and identify optimal surgical treatment (Jenkins et al., 2023). Based on Jenkins’ classification, there are 9 types of LSTV:

Type 1:

Type I: Overgrowth of one or both transverse processes of the measuring at least 19mm in width

Type II: One or both transverse processes are enlarged enough to form a pseudo-articulation (i.e., false joint) with the sacral ala.

Type III: There is complete fusion of both transverse processes to the sacral ala, i.e., a complete sacralization of the last lumbar segment.

Type IV: Mixed anatomy where one side forms a pseudo-articulation whereas the other side is fully fused to the sacral ala.

Type 1A: Enlarged transverse process on the last lumbar segment with less than 10mm gap, but over 2mm gap, between the transverse process and sacral ala on one side only. The other side has “normal” distance over 10mm.

Type 1IB: Both transverse processes of the last lumbar segment has less than 10mm gap, but over 2mm gap, between the transverse process and sacral ala.

Type 2:

Type 2A: Incomplete lumbarization/sacralization with enlarged transverse process that creates a pseudoarticulation with itself and the sacrum (less than 2mm distance) on one side only. The other side has “normal” distance of above 10mm.

Type 2B: Symmetrical anatomy where both transverse processes have a pseudo-articulation on both sides with the sacrum with less than 2mm distance.

Type 2C: Hybrid anatomy where one transverse process has Type II anatomy (i.e., forms pseudo-articulation with the sacrum) and the other transverse process has Type IA anatomy (i.e., has between 2mm to 10mm distance between itself and the sacrum).

Type 3:

Type 3: Bilateral lumbarization/sacralization with complete osseous (bone) fusion of the transverse processes to the sacrum.

Type 4:

Type 4A: Lumbarization/sacralization with complete osseous fusion of transverse process to the sacrum on one side only. The other side has Type I anatomy with transverse process at distance of less than 10mm from sacrum.

Type 4B: Lumbarization/sacralization with complete osseous fusion (i.e., Type 3 like anatomy) on one side and an incomplete lumbarization/sacralization of the transverse process on other side (i.e., type 2 like anatomy).

Type 4C: Lumbarization/sacralization with complete osseous fusion of transverse process to the sacrum on one side only. The other side has “normal” anatomy with transverse process at distance of more than 10mm from sacrum.

References:

Alonzo, F., Cobar, A., Cahueque, M., & Prieto, J. A. (2018). Bertolotti’s syndrome: An underdiagnosed cause for lower back pain. Journal of Surgical Case Reports, 2018(10), rjy276. https://doi.org/10.1093/jscr/rjy276

Castellvi, A. E., Goldstein, L. A., & Chan, D. P. K. (1984). Lumbosacral Transitional Vertebrae and Their Relationship With Lumbar Extradural Defects. Spine, 9(5), 493.

Jenkins, A. L., O’Donnell, J., Chung, R. J., Jenkins, S., Hawks, C., Lazarus, D., McCaffrey, T., Terai, H., & Harvie, C. (2023). Redefining the Classification for Bertolotti Syndrome: Anatomical Findings in Lumbosacral Transitional Vertebrae Guide Treatment Selection. World Neurosurgery, 175, e303–e313. https://doi.org/10.1016/j.wneu.2023.03.077

Kapetanakis, S., Chaniotakis, C., Paraskevopoulos, C., & Pavlidis, P. (2017). An Unusual Case Report of Bertolotti’s Syndrome: Extraforaminal Stenosis and L5 Unilateral Root Compression (Castellvi Type III an LSTV). Journal of Orthopaedic Case Reports, 7(3), 9–12. https://doi.org/10.13107/jocr.2250-0685.782

McGrath, K., Schmidt, E., Rabah, N., Abubakr, M., & Steinmetz, M. (2021). Clinical assessment and management of Bertolotti Syndrome: A review of the literature. The Spine Journal, 21(8), 1286–1296. https://doi.org/10.1016/j.spinee.2021.02.023

Zhu, W., Ding, X., Zheng, J., Zeng, F., Zhang, F., Wu, X., Sun, Y., Ma, J., & Yin, M. (2023). A systematic review and bibliometric study of Bertolotti’s syndrome: Clinical characteristics and global trends.