Biomechanical influence of numerical variants of lumbosacral transitional vertebra with Castellvi type I on adjacent discs and facet joints based on 3D finite element analysis

Objectives

To investigate the effect of lumbosacral transitional vertebra (LSTV) on the biomechanical properties of adjacent discs and facet joints based on geometrically 3D personalized FEA.

Methods

A total of 45 individuals who underwent low dose whole body CT scans were retrospectively included and equally divided into 23, 24, and 25 presacral vertebrae (PSV) groups. Three-dimensional Finite Element computational models of normal and number-variant sub-types of LSTV were created. The biomechanical parameters, including the range of motion (ROM), the intervertebral disc pressure (IDP), and facet joint forces (FJF), were all evaluated to determine the biomechanical effects. IDP was equally divided into anterior (AIDP), middle (MIDP) and posterior (PIDP) parts along the short axis of the intervertebral disc.

Results

During extension, the 23 PSV group exhibited significantly higher von Meiss stress in the upper intervertebral disc compared to the 24 and 25 PSV groups (P = 0.003), indicating concentrated stress in the upper lumbar region and an increased the likelihood of localized disc degeneration over time. Furthermore, the 23 PSV group exhibited a larger ROM (3.28°) than the 25 PSV group (1.40°) (P = 0.011), implying greater segmental mobility and possible instability in the transitional segment. During flexion, the 25 PSV group showed higher stress in the lower intervertebral disc and a larger ROM than the 23 and 24 PSV groups; however, the differences were not significant (P > 0.05).

Conclusions

The increased stress distribution and ROM in the upper disc of the transitional segment were only found in the 23 PSV sub-type of Castellvi type I LSTVs during extension, but not in the 25 PSV sub-type, which may help to further understand the impact of LSTV on the surrounding structures.