寰枕融合的形态生物力学分析

Morphological and Biomechanical Analysis of Inferior Articular Facets of Atlas in Patients with Occipitalization of Atlas

目的研究寰枕融合患者寰椎下关节面几何形态学特征。方法35例寰枕融合患者CT扫描后,CT数据通过三维可视化软件(Amira4.0)重建寰椎下关节面和相关颅颈交界结构的几何形态。基于由Frankfort水平平面(FHP)、垂直于FHP的矢状平面和冠状平面构成的三维参考平面,测量关节面前后方向和侧方向空间成角。结果35例中28例双侧、3例单侧寰椎下关节面前倾角大于10°,均表现为前后脱位、旋转脱位和颅骨下沉等不同类型的脱位。4例双侧关节面前倾角小于10°,除1例外均无明显寰枢关节无脱位。两侧关节面的空间成角呈现不对称者常见。结论寰枕融合时寰枢椎之间承重关节常呈现不同程度的前倾和不对称,这种几何形态变化导致的关节生物力学变化有可能是寰枢椎脱位的直接原因。

Objective To study the geometric characteristics of inferior articular facets of the atlas in patients with occipitalization of atlas. Methods CT data of 35 cases of occipitalization of atlas were reconstructed hy the three-dimensional visualization software （Amira 4.0） to display the inferior articular facets of the atlas as well as related craniovertebral structures. Measurements were performed based on three reference planes including axial plane paralleled to the Frankfort horizontal plane （FHP）, sagittal plane perpendicular to the FHP, and coronal plane perpendicular to the two aforementioned planes. After the facet plane was reconstructed to fit the orientation of the inferior articular facets of the atlas, and the three reference planes were set up, the spatial angulations between the facet plane and FHP were measured on the sagittal and coronal planes. Results The bilateral facet forward inclination angles of greater than 10° on the sagittal plane were observed in 28 patients and unilateral in 3. There were with various types of atlantoaxial dislocation including forward or backward dislocation, rotational dislocation, and so-called cranial settling in these patients. There was not atlantoaxial dislocation in 3 of 4 patients with the facet angles of no greater than 10°. Asymmetrical angulation on both the sagittal and coronal planes was common in all the patients. Conclusion The biomechanical changes produced by the forward tilting and asymmetric articulations in the load-bearing joints of atlantoaxial complex which are common in patients with occipitalization of the atlas may be a more direct cause of atlantoaxial dislocation in these patients.