Xi Zhipeng, Xie Yimin, Sun Shenglu, Hu Fei, Li Jingchi
Department of Orthopedics, Affiliated Hospital of Integrated Traditional Chinese and Western Medicine, Nanjing University of Chinese Medicine, Nanjing, China.
Department of Orthopedics, Traditional Chinese Medicine Hospital of Ili Kazak Autonomous Prefecture, Yining, China.
Bone Joint Res. 2025 Sep 4;14(9):777-790. doi: 10.1302/2046-3758.149.BJR-2024-0461.R2.
Intervertebral disc degeneration (IDD) and sagittal-oriented articular processes can restrict motility and increase stiffness of the motion segment, potentially causing compensatory stress and higher motility in adjacent segments. It is unclear if these factors trigger IDD progression in adjacent segments. This study aimed to elucidate this using functional MRI, and identify biomechanical mechanisms with a validated numerical model.
Clinical data from 95 patients were retrospectively collected from January 2022 to April 2023. Disc collapse and fibrosis were assessed by disc height ratio and fractional anisotropy (FA) values in the L4-L5 segment. The orientation of articular facet processes in L4-L5 was examined. Annulus fibrosus integrity was investigated using diffusion tensor fibre tractography in cranial (L3-L4) and caudal (L5-S1) segments. Statistical analyses determined differences between patients with and without annulus tears, and regression analyses identified predictors of annulus tears. Numerical models of L3-S1 motion segment were developed, incorporating variations in disc collapse, fibrosis, and facet orientation angles in L4-L5. Stress distribution on cranial and caudal discs was calculated under various loading conditions.
Compared to patients with intact annulus at the cranial segment (L3-L4), those with annulus tears show reduced facet orientation angles and disc height ratios, and elevated FA values. These parameters are independent risk factors for cranial annulus tears, not observed on the caudal side. Models with sagittal-oriented articular processes (facet orientation = 35°), disc collapse, and fibrosis show higher stress on the cranial disc, particularly within the annulus, compared to models with coronal-oriented processes (facet orientation = 65°) and healthy discs.
Sagittal orientation of articular processes and IDD phenotypes may increase the risk of annulus tears in the cranial adjacent segment by compromising the biomechanical environment. This offers a novel perspective for understanding biomechanical interactions in adjacent segments during IDD progression.
椎间盘退变（IDD）和矢状位定向的关节突可限制运动节段的活动度并增加其僵硬程度，可能导致相邻节段出现代偿性应力和更高的活动度。目前尚不清楚这些因素是否会引发相邻节段的IDD进展。本研究旨在通过功能磁共振成像对此进行阐明，并使用经过验证的数值模型确定生物力学机制。
回顾性收集了2022年1月至2023年4月期间95例患者的临床数据。通过L4-L5节段的椎间盘高度比和分数各向异性（FA）值评估椎间盘塌陷和纤维化情况。检查L4-L5关节突关节的方向。使用扩散张量纤维束成像技术在头侧（L3-L4）和尾侧（L5-S1）节段研究纤维环的完整性。统计分析确定有无纤维环撕裂患者之间的差异，回归分析确定纤维环撕裂的预测因素。建立了L3-S1运动节段的数值模型，纳入了L4-L5节段椎间盘塌陷、纤维化和关节突方向角度的变化。计算了在各种加载条件下头侧和尾侧椎间盘的应力分布。
与头侧节段（L3-L4）纤维环完整的患者相比，有纤维环撕裂的患者关节突方向角度和椎间盘高度比降低，FA值升高。这些参数是头侧纤维环撕裂的独立危险因素，在尾侧未观察到。与冠状位定向的关节突（关节突方向 = 65°）和健康椎间盘的模型相比，矢状位定向的关节突、椎间盘塌陷和纤维化的模型在头侧椎间盘上显示出更高的应力，尤其是在纤维环内。
关节突的矢状位定向和IDD表型可能通过损害生物力学环境增加相邻头侧节段纤维环撕裂的风险。这为理解IDD进展过程中相邻节段的生物力学相互作用提供了一个新的视角。
