Biomechanical analysis of the interlaminar dynamic stabilization system (IntraSPINE) in unilateral biportal...

To investigate the biomechanical effects of the IntraSPINE (Cousin Biotech, Wervicq-Sud, France) interlaminar distraction device on both the operated and adjacent spinal segments during unilateral biportal endoscopic (UBE) discectomy for huge lumbar disc herniation (HLDH) in young patients.

Based on preoperative and postoperative CT data of a patient with a single-segment, large lumbar disc herniation at the L4-5 segment, a three-dimensional finite element model of the L1-S1 segments was established. Three models were constructed: a preoperative model (M1), a postoperative model without IntraSPINE implantation after unilateral discectomy (M2), and a postoperative model with IntraSPINE implantation (M3). After model validation, a 500 N axial load and a 10 N·m moment were applied to simulate six motion conditions. A comparative analysis was performed on the range of motion (ROM), intradiscal pressure, maximum von Mises stress in the annulus, and maximum shear stress in the annulus at each segment from L3 to S1, as well as the facet joint stress at the L4-5 segment.

Compared with the M1 model, the M2 model exhibited a significant increase in mobility at the L4-5 segment, with the most pronounced rise ROM observed during right bending-an increase of 36.8%. Increases of 31.5% and 14.9% were also noted during left bending and left axial rotation, respectively. The intradiscal pressure at this segment increased by 59.7% during flexion, while the maximum von Mises stress in the annulus rose by 82.4% during right axial rotation, and the shear stress increased by 95.2% during extension. Additionally, the stress on the right facet joint (surgical side) peaked at 6.8799 MPa during left bending, which was significantly higher than in the M1 model, indicating reduced segmental stability and marked stress concentration. This was accompanied by compensatory increases in both mobility and stress in adjacent segments. In contrast, the M3 model demonstrated a downward trend in all biomechanical indicators at the L4-5 segment. ROM decreased by 33.2% during flexion, intradiscal pressure decreased by 58.4% during extension, maximum von Mises stress in the annulus decreased by 32.3% during left axial rotation, and shear stress dropped by 88.9% during left axial rotation. The maximum stress on the right facet joint during left bending was reduced to 2.8862 MPa, which was significantly lower than in both M2 and M1 models. No abnormal increase in motion or stress was observed in the adjacent segments.

The IntraSPINE dynamic stabilization system combined with UBE discectomy surgery offers significant biomechanical advantages in the treatment of HLDH. Its unique dynamic stabilization properties can effectively maintain intervertebral height, preserve partial mobility of the operated and adjacent segments, and alleviate postoperative stress concentration on the intervertebral disc and facet joints. Therefore, it may serve as a promising treatment option for HLDH patients.