Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15238, USA.
Spine (Phila Pa 1976). 2009 Dec 1;34(25):2792-6. doi: 10.1097/BRS.0b013e3181b61e00.
The use of lumbar fusion cages to augment interbody arthrodesis has become popular. Previous studies have shown that titanium cages may obscure information within and around the cage, confounding assessments of fusion. Densitometry within cages, if possible, could be an important outcome variable for comparing different cage augmented fusion treatments.
The purpose of this feasibility study was to (1) validate CT-based (computer tomography-based) density evaluations within titanium cages in a phantom model, and (2) demonstrate that intrametal cage lucencies can be produced by CT reconstruction artifacts and do not necessarily represent bone fragmentation or fibrous and cartilaginous tissue.
An anthropomorphic lumbar spine phantom was used. Dual titanium cages were inserted into 6 anterior-middle column replicas, and the cages were filled with 10, 100, or 400 mg/cc hydoxyapatiite equivalent material. The column replicas were composed of either fibrous/cartilaginous tissue equivalent material or trabecular bone equivalent material. Column replicas were placed within the phantom and imaged with CT. Direct axial and reformatted sagittal and coronal images were evaluated for artifact. Region of interest analysis was performed for intracage density.
Intracage CT values calculated from axial, sagittal, and coronal images were directly related to the true CT values of the materials (r = 0.99, P < 0.0001). CT was used to distinguish between fibrous tissue and bone within cages. CT values within cages overestimated the intracage materials' true values (paired t test, P < 0.001). Intracage CT values were correctable and could be converted to bone mineral content. Intracage CT values were not affected by adjacent anterior-middle column material differences (fibrous/cartilaginous tissue vs. trabecular bone) (paired t test, P > 0.05). Lucent streaking within and adjacent to cages was similar to clinical images.
In this phantom-based study, densitometry was performed within titanium cages, even in the presence of CT artifact. These results support further pursuit of this potential assessment tool.
使用腰椎融合 cage 来增强椎间融合已变得流行。先前的研究表明，钛 cage 可能会使 cage 内部和周围的信息变得模糊，从而影响对融合的评估。如果可能的话，cage 内的密度测定可以成为比较不同 cage 增强融合治疗的重要结果变量。
本可行性研究的目的是：（1）验证在体模中基于 CT 的（计算机断层扫描）钛 cage 内的密度评估，以及（2）证明 intrametal cage 内的透光性是由 CT 重建伪影引起的，不一定代表骨碎片或纤维和软骨组织。
使用人体腰椎体模。将两个钛 cage 插入 6 个前中柱复制品中，并用 10、100 或 400mg/cc 羟基磷灰石等效物填充 cage。柱复制品由纤维/软骨组织等效物或小梁骨等效物组成。将柱复制品放置在体模内并进行 CT 成像。对直接轴向和重建成像矢状位和冠状位图像进行评估以发现伪影。对 cage 内的感兴趣区域进行密度分析。
从轴向、矢状位和冠状位图像计算的 cage 内 CT 值与材料的真实 CT 值直接相关（r=0.99，P<0.0001）。CT 可用于区分 cage 内的纤维组织和骨。cage 内的 CT 值高估了 cage 内材料的真实值（配对 t 检验，P<0.001）。cage 内的 CT 值可校正，并可转换为骨矿物质含量。cage 内的 CT 值不受相邻前中柱材料差异（纤维/软骨组织与小梁骨）的影响（配对 t 检验，P>0.05）。cage 内和周围的透光条纹与临床图像相似。
在这项基于体模的研究中，即使存在 CT 伪影，也可以在钛 cage 内进行密度测定。这些结果支持进一步探索这种潜在的评估工具。
