Computed tomography and finite element modeling were used to assess bone structure at the knee as a function of time after spinal cord injury. Analyzed regions experienced degradation in stiffness, mineral density, and content. Changes were well described as an exponential decay over time, reaching a steady state 3.5 years after injury. INTRODUCTION Spinal cord injury (SCI) is associated with bone fragility and an increased risk of fracture around the knee. The purpose of this study was to investigate bone stiffness and mineral content at the distal femur and proximal tibia, using finite element (FE) and computed tomography (CT) measures. A cross-sectional design was used to compare differences between non-ambulatory individuals with SCI as a function of time after injury (0-50 years). METHODS CT scans of the knee were obtained from 101 individuals who experienced an SCI 30 days to 50 years prior to participation. Subject-specific FE models were used to estimate stiffness under axial compression and torsional loading, and CT data was analyzed to assess volumetric bone mineral density (vBMD) and bone mineral content (BMC) for integral, cortical, and trabecular compartments of the epiphyseal, metaphyseal, and diaphyseal regions of the distal femur and proximal tibia. RESULTS Bone degradation was well described as an exponential decay over time (R2 = 0.33-0.83), reaching steady-state levels within 3.6 years of SCI. Individuals at a steady state had 40 to 85% lower FE-derived bone stiffness and robust decreases in CT mineral measures, compared to individuals who were recently injured (t ≤ 47 days). Temporal and spatial patterns of bone loss were similar between the distal femur and proximal tibia. CONCLUSIONS After SCI, individuals experienced rapid and profound reductions in bone stiffness and bone mineral at the knee. FE models predicted similar reductions to axial and torsional stiffness, suggesting that both failure modes may be clinically relevant. Importantly, CT-derived measures of bone mineral alone underpredicted the impacts of SCI, compared to FE-derived measures of stiffness. TRIAL REGISTRATION ClinicalTrials.gov (NCT01225055, NCT02325414).

中文翻译：

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脊髓损伤后的骨脆性：股骨远端和胫骨近端的硬度和骨矿物质随时间的变化而减少。


使用计算机断层扫描和有限元建模来评估脊髓损伤后膝关节骨结构随时间的变化。分析区域的硬度、矿物密度和含量均出现下降。变化被很好地描述为随着时间的推移呈指数衰减，在受伤后 3.5 年达到稳定状态。简介 脊髓损伤 (SCI) 与骨质脆性和膝盖周围骨折的风险增加有关。本研究的目的是利用有限元 (FE) 和计算机断层扫描 (CT) 测量来研究股骨远端和胫骨近端的骨硬度和矿物质含量。采用横断面设计来比较患有 SCI 的非行走个体之间的差异，作为受伤后时间（0-50 年）的函数。方法 对 101 名在参与前 30 天至 50 年经历过 SCI 的人进行膝部 CT 扫描。使用特定于受试者的有限元模型来估计轴向压缩和扭转载荷下的刚度，并分析 CT 数据以评估骨骺的整体、皮质和小梁室的体积骨矿物质密度 (vBMD) 和骨矿物质含量 (BMC)。股骨远端和胫骨近端的干骺端和骨干区域。结果 骨退化被很好地描述为随时​​间呈指数衰减（R2 = 0.33-0.83），在 SCI 后 3.6 年内达到稳态水平。与最近受伤（t ≤ 47 天）的个体相比，处于稳定状态的个体 FE 衍生的骨硬度降低 40% 至 85%，CT 矿物质测量值显着下降。股骨远端和胫骨近端骨丢失的时间和空间模式相似。 结论 SCI 后，患者膝关节的骨硬度和骨矿物质迅速而显着降低。有限元模型预测了轴向刚度和扭转刚度的类似降低，表明这两种失效模式可能具有临床相关性。重要的是，与 FE 衍生的硬度测量相比，仅 CT 衍生的骨矿物质测量结果低估了 SCI 的影响。试验注册 ClinicalTrials.gov（NCT01225055、NCT02325414）。