Dept of Oncology and Metabolism, INSIGNEO Institute for In Silico Medicine, University of Sheffield, Sheffield, UK; Dept of Industrial Engineering, Alma Mater Studiorum - University of Bologna, Bologna, Italy.
Dept of Spine Surgery, IRCCS Istituto Ortopedico Rizzoli, Bologna, Italy.
Bone. 2021 Oct;151:116028. doi: 10.1016/j.bone.2021.116028. Epub 2021 Jun 2.
Bone metastases may lead to spine instability and increase the risk of fracture. Scoring systems are available to assess critical metastases, but they lack specificity, and provide uncertain indications over a wide range, where most cases fall. The aim of this work was to use a novel biomechanical approach to evaluate the effect of lesion type, size, and location on the deformation of the metastatic vertebra.
Vertebrae with metastases were identified from 16 human spines from a donation programme. The size and position of the metastases, and the Spine Instability Neoplastic Score (SINS) were evaluated from clinical Quantitative Computed Tomography images. Thirty-five spine segments consisting of metastatic vertebrae and adjacent healthy controls were biomechanically tested in four different loading conditions. The strain distribution over the entire vertebral bodies was measured with Digital Image Correlation. Correlations between the features of the metastasis (type, size, position and SINS) and the deformation of the metastatic vertebrae were statistically explored.
The metastatic type (lytic, blastic, mixed) characterizes the vertebral behaviour (Kruskal-Wallis, p = 0.04). In fact, the lytic metastases showed more critical deformation compared to the control vertebrae (average: 2-fold increase, with peaks of 14-fold increase). By contrast, the vertebrae with mixed or blastic metastases did not show a clear trend, with deformations similar or lower than the controls. Once the position of the lytic lesion with respect to the loading direction was taken into account, the size of the lesion was significantly correlated with the perturbation to the strain distribution (r = 0.72, p < 0.001). Conversely, the SINS poorly correlated with the mechanical evidence, and only in case of lytic lesions (r = 0.25, p < 0.0001).
These results highlight the relevance of the size and location of the lytic lesion, which are marginally considered in the current clinical scoring systems, in driving the spinal biomechanical instability. The strong correlation with the biomechanical evidence indicates that these parameters are representative of the mechanical competence of the vertebra. The improved explanatory power compared to the SINS suggests including them in future guidelines for the clinical practice.
骨转移可能导致脊柱不稳定并增加骨折风险。现已有评估关键转移病灶的评分系统，但这些系统缺乏特异性，在大多数病例中，其提供的指示范围较广且不确定。本研究旨在采用新的生物力学方法评估病灶类型、大小和位置对转移椎体变形的影响。
从捐赠项目中的 16 个人体脊柱中鉴定出带有转移病灶的椎体。从临床定量 CT 图像中评估转移病灶的大小和位置以及脊柱不稳定性肿瘤评分（SINS）。在四种不同的加载条件下，对 35 个包含转移椎体和相邻健康对照的脊柱节段进行生物力学测试。使用数字图像相关技术测量整个椎体的应变分布。统计分析转移病灶的特征（类型、大小、位置和 SINS）与转移椎体变形之间的相关性。
转移病灶的类型（溶骨性、成骨性、混合性）决定了椎体的行为（Kruskal-Wallis，p=0.04）。实际上，与对照椎体相比，溶骨性转移病灶表现出更严重的变形（平均增加 2 倍，峰值增加 14 倍）。相比之下，混合性或成骨性转移病灶没有表现出明显的趋势，其变形与对照相似或更低。一旦考虑到溶骨性病变相对于加载方向的位置，病变的大小与应变分布的干扰显著相关（r=0.72，p<0.001）。相反，SINS 与力学证据相关性较差，仅在溶骨性病变的情况下相关（r=0.25，p<0.0001）。
这些结果强调了溶骨性病变的大小和位置的重要性，而这些因素在当前的临床评分系统中仅略有考虑，是导致脊柱生物力学不稳定的因素。与生物力学证据的强相关性表明，这些参数代表了椎体的力学能力。与 SINS 相比，其解释能力有所提高，这表明在未来的临床实践指南中应将这些参数纳入其中。
