Alonso Fernando, Iwanaga Joe, Chapman Jens R, Oskouian Rod J, Tubbs R Shane
Swedish Neuroscience Institute, Seattle, Washington, USA; Department of Neurosurgery, University Hospitals of Cleveland, Cleveland, Ohio, USA.
Seattle Science Foundation, Seattle, Washington, USA.
World Neurosurg. 2017 Aug;104:132-135. doi: 10.1016/j.wneu.2017.05.029. Epub 2017 May 13.
Type 2 odontoid fractures are the most common cervical fractures among the elderly. Neurologic deficit is usually caused by myelopathy as a result of posterior dens migration. Direct anterior screw placement provides stabilization and can preserve C1-C2 movement. The presence of a bony excrescence on the anterior superior tip of the dens may lead to placement of a screw of incorrect length.
Twenty C2 dry specimens were examined for the presence of a corona dentis, which is a bony excrescence in the coronal plane near the apex of the dens. When identified, measurements of the corona dentis were performed using calipers and a ruler. In addition, anteroposterior (AP) and lateral fluoroscopy was performed on all specimens found to have a corona dentis.
A corona dentis was found on 20% of our C2 specimens and had an average width of 9 mm and an average height of 4.5 mm. The average width of the dens did not vary as the normal tip of the dens transitioned into the coronae. In no specimen did the corona dentis seem to be composed of trabecular bone and it was seen as a superior projection of cortical bone on fluoroscopy. On fluoroscopy, the corona dentis could be identified on a true AP projection. In angulated AP views, fluoroscopic images overestimated the length of the corona dentis.
We describe a new entity termed the corona dentis because of its crownlike feature. It is a superior cortical bone protrusion and should be noted as a variant of the dens during anterior odontoid screw placement. Its propensity to increase the height of the dens markedly can lead to higher rates of neurologic deficits during type 2 odontoid fractures if not appreciated. A true AP view is critical for correct screw size placement.
Ⅱ型齿状突骨折是老年人中最常见的颈椎骨折。神经功能缺损通常是由于齿状突后方移位导致的脊髓病引起的。直接前路螺钉置入可提供稳定性并能保留C1-C2节段的活动度。齿状突前上尖端的骨质增生可能导致置入长度不正确的螺钉。
对20个C2椎体干燥标本检查是否存在齿冠，齿冠是齿状突尖部冠状面的骨质增生。确定存在齿冠后，使用卡尺和直尺对其进行测量。此外，对所有发现有齿冠的标本进行前后位（AP）和侧位透视。
在我们的20%的C2标本上发现了齿冠，其平均宽度为9mm，平均高度为4.5mm。当齿状突的正常尖端过渡到齿冠时，齿状突的平均宽度没有变化。在任何标本中，齿冠似乎都不是由小梁骨组成，在透视下它被视为皮质骨的上突。在透视下，齿冠可在真正的前后位投照中识别。在成角的前后位视图中，透视图像高估了齿冠的长度。
由于其冠状样特征，我们描述了一种新的实体，称为齿冠。它是一种皮质骨上突，在进行前路齿状突螺钉置入时应作为齿状突的一种变异加以注意。如果未被认识到，其显著增加齿状突高度的倾向可能导致Ⅱ型齿状突骨折时更高的神经功能缺损发生率。真正的前后位视图对于正确放置螺钉尺寸至关重要。
