Hsiao Chih-Kun, Hsiao Hao-Yuan, Tsai Yi-Jung, Hsu Chao-Ming, Tu Yuan-Kun
Department of Medical Research, E-Da Hospital, I-Shou University, Kaohsiung 824, Taiwan.
Department of Orthopedics, E-Da Hospital, I-Shou University, Kaohsiung 824, Taiwan.
Bioengineering (Basel). 2023 Sep 5;10(9):1042. doi: 10.3390/bioengineering10091042.
Spinal fusion surgery leads to the restriction of mobility in the vertebral segments postoperatively, thereby causing stress to rise at the adjacent levels, resulting in early degeneration and a high risk of adjacent vertebral fractures. Thus, to address this issue, non-fusion surgery applies some pedicle screw-based dynamic stabilisation systems to provide stability and micromotion, thereby reducing stress in the fusion segments. Among these systems, the hybrid performance stabilisation system (HPSS) combines a rigid rod, transfer screw, and coupler design to offer a semi-rigid fixation method that preserves some mobility near the fusion site and reduces the adjacent segment compensatory effects. However, further research and confirmation are needed regarding the biomechanical effects of the dynamic coupler stiffness of the HPSS on the intrinsic degenerated adjacent segment. Therefore, this study utilised the finite element method to investigate the impact of the coupler stiffness of the HPSS on the mobility of the lumbar vertebral segments and the stress distribution in the intervertebral discs under flexion, extension, and lateral bending, as well as the clinical applicability of the HPSS on the discs with intrinsic moderate and severe degeneration at the adjacent level. The analytical results indicated that, regardless of the degree of disc degeneration, the use of a dynamic coupler stiffness of 57 N/mm in the HPSS may reduce the stress concentrations at the adjacent levels. However, for severely degenerated discs, the postoperative stress on the adjacent segments with the HPSS was still higher compared with that of the discs with moderate degeneration. We conclude that, when the discs had moderate degeneration, increasing the coupler stiffness led to a decrease in disc mobility. In the case of severe disc degeneration, the effect on disc mobility by coupler stiffness was less pronounced. Increasing the coupler stiffness ked to higher stress on intervertebral discs with moderate degeneration, while its effect on stress was less pronounced for discs with severe degeneration. It is recommended that patients with severe degeneration who undergo spinal dynamic stabilisation should remain mindful of the risk of accelerated adjacent segment degeneration.
脊柱融合手术会导致术后椎体节段活动受限，从而使相邻节段的应力增加，导致早期退变以及相邻椎体骨折的高风险。因此，为了解决这个问题，非融合手术应用了一些基于椎弓根螺钉的动态稳定系统来提供稳定性和微动，从而降低融合节段的应力。在这些系统中，混合性能稳定系统（HPSS）结合了刚性杆、转接螺钉和耦合器设计，提供了一种半刚性固定方法，可保留融合部位附近的一些活动度，并减少相邻节段的代偿效应。然而，关于HPSS动态耦合器刚度对内在退变相邻节段的生物力学影响，还需要进一步的研究和证实。因此，本研究利用有限元方法，研究HPSS耦合器刚度对腰椎节段活动度以及屈伸和侧弯时椎间盘应力分布的影响，以及HPSS在相邻节段存在中度和重度内在退变椎间盘上的临床适用性。分析结果表明，无论椎间盘退变程度如何，在HPSS中使用57 N/mm的动态耦合器刚度可能会降低相邻节段的应力集中。然而，对于严重退变的椎间盘，与中度退变的椎间盘相比，使用HPSS时相邻节段的术后应力仍然更高。我们得出结论，当椎间盘为中度退变时，增加耦合器刚度会导致椎间盘活动度降低。在严重椎间盘退变的情况下，耦合器刚度对椎间盘活动度的影响不太明显。增加耦合器刚度会导致中度退变椎间盘的应力更高，而对严重退变椎间盘的应力影响不太明显。建议接受脊柱动态稳定手术的严重退变患者应始终注意相邻节段加速退变的风险。
