Diab K M, Ollmar S, Sevastik J A, Willers U, Svensson A
Department of Orthopaedic Surgery, Huddinge University Hospital, Karolinska Institute, Sweden.
Eur Spine J. 1998;7(4):282-8. doi: 10.1007/s005860050076.
A new method is presented for stereological evaluation of the volume of the vertebral body in vivo. The height of the vertebral body is measured at three standardised points on an anteroposterior radiograph and at two other points on a lateral one. The area of the body is also measured using a special grid superimposed on a CT scan from the middle part of the vertebra. The volume of the vertebral body is then calculated using Cavalieri's principle for irregular objects: V = delta a x H, where V is the volume of the vertebral body, delta a is the mean cross-section surface area on the CT scan and H is the mean of the heights at the five points on the radiographs, computed as mean weighted circumferential height. The volume of one normal and one scoliotic vertebra was evaluated in vitro using this formula. The obtained values were compared with the values derived from serial CT scans of the two vertebrae. The results showed that the volume of the normal vertebra measured with our new method was 15.9 cm3 and measured with serial CT scans using the same grid it was 15.07 cm3. For the scoliotic vertebra the values were 17.6 and 17.3 cm3, respectively. The degree of accuracy of the measurements with the presented method as compared with the serial CT method was 95% for the normal and 98.5% for the scoliotic vertebra. To prove the clinical applicability of the method, the heights of the apical and of the upper and the lower end vertebrae of the curve and the volume of the apical vertebrae were evaluated in eight scoliotic girls (nine curves) before and 3 years after spinal instrumentation and posterior fusion. The results showed that the mean circumferential height of the three vertebrae had increased significantly at the last follow-up. The volume of the apical vertebra had also increased, but the difference was not significant. It is concluded that the described method is easy to apply and has satisfactory accuracy for in vivo longitudinal studies of the volume of the vertebral body on radiographs and CT scans.
本文介绍了一种在体立体测量椎体体积的新方法。在前后位X线片上的三个标准化点以及侧位X线片上的另外两个点测量椎体高度。还使用叠加在椎体中部CT扫描上的特殊网格测量椎体面积。然后根据卡瓦列里原理计算不规则物体的椎体体积：V = Δa × H，其中V为椎体体积，Δa为CT扫描上的平均横截面积，H为X线片上五个点高度的平均值，计算为平均加权圆周高度。使用该公式在体外评估了一个正常椎体和一个脊柱侧弯椎体的体积。将获得的值与通过对两个椎体进行连续CT扫描得出的值进行比较。结果显示，用我们的新方法测量的正常椎体体积为15.9 cm³，使用相同网格通过连续CT扫描测量的值为15.07 cm³。对于脊柱侧弯椎体，相应的值分别为17.6 cm³和17.3 cm³。与连续CT方法相比，该方法测量的正常椎体的准确度为95%，脊柱侧弯椎体为98.5%。为了证明该方法的临床适用性，在八名脊柱侧弯女孩（九条曲线）进行脊柱内固定和后路融合术前及术后3年，评估了曲线顶点、上端和下端椎体的高度以及顶点椎体的体积。结果显示，在最后一次随访时，三个椎体的平均圆周高度显著增加。顶点椎体的体积也有所增加，但差异不显著。结论是，所述方法易于应用，对于在X线片和CT扫描上对椎体体积进行体内纵向研究具有令人满意的准确度。
