寰椎椎弓根形态分类与椎弓根螺钉植钉方法研究

目的探讨寰椎椎弓根形态分类及椎弓根螺钉固定的植钉方法。方法寰椎椎弓根形态分类研究：取成人干燥寰椎标本48个，行CT三维重建，建立经过椎动脉沟底部下2mm处横切面和椎弓根中外1／3矢状面的切面图：以螺钉直径3．50mm，半径1．75mm为标准，根据通过椎弓根中外1／3矢状面的椎动脉沟底部骨质厚度，将寰椎椎弓根解剖形态分为3型：普通型40个（83％），轻度变异型6个（13％），重度变异型2个（4％）。以通过寰椎椎弓根中外1／3矢状面与通过椎动脉沟底部下方约2mm处横断面的交线为进钉通道，以进钉通道在后弓后方骨皮质上的投影点为进钉点，采用电子游标卡尺在干燥寰椎骨标本上测量以下指标：进钉点与侧块后缘的距离（L1），进钉处寰椎椎弓根高度（L2），进钉点至侧块下关节面的垂直距离（L3），进钉处侧块高度（L4），进钉处侧块宽度（L5），进钉处寰椎椎弓根宽度（L6），钉道处椎动脉沟底椎弓根厚度（H1）。寰椎椎弓根螺钉植钉方法的研究：取12个新鲜成人冷冻寰椎标本，左右侧钉道处椎动脉沟底部骨质厚度分别打磨为：1．5mm和2．5mm，1．5mm和4．0mm，2．5mm和4．0mm，每种厚度4个标本；以通过寰椎椎弓根的中外1／3矢状面与通过椎动脉沟底部下约2mm处横断面的交线为进钉通道植钉。结果左侧L1（5．79±1．24）mm，L2（4．55±1．29）mm，L3（5．12±1．06）mm，L4（12．43±1．01）mm，L5（12．66±1.37）mm，L6（7．86±0．77）mm，H1（4．11±1．25）mm；右侧0L1（5．81±1．26）mm，L2（4．49±1．22）mm，L3（5．15±1．05）mm，L4（12．49±0．98）mm，L5（12．65±1．38）mm，L6（7．84±0．78）mm，H1（4．13±1．29）mm；两侧比较差异均无统计学意义（P〉0．05）。模拟植钉后所有标本无螺钉向上突破椎动脉沟底骨质。结论对于寰椎后弓高度偏小的患者，可部分经寰椎后弓或跨越寰椎后弓实现寰椎的椎弓根螺钉固定，进钉位置应以术前三维CT重建和术中探查结合考虑。

CLASSIFICATION OF ATLAS PEDICLES AND METHODOLOGICAL STUDY OF PEDICLE SCREW FIXATION

OBJECTIVE: To investigate the classification of atlas pedicles and the methods of the pedicle screw fixation. METHODS: To study the classification of atlas pedicles, 48 dry adult atlas specimens were measured. By atlas 3D-CT reconstruction, two transverse sections were established by going through the one third of the lateral atlas pedicle and 2 mm below the vertebral artery sulcus. By setting 3.50 mm and 1.75 mm as the standardized diameter and radius for the screw and according to the thickness of bone substance of vertebral artery sulcus that went through the one third of the lateral atlas pedicle, the anatomical morphology of atlas pedicles were classified into three types: general type with 40 specimens (83%), light variation type with 6 specimens (13%), and severe variation type with 2 specimens (4%). The entry pathway was confirmed by the intersection line of the two transverse sections that went through the lateral one third of the atlas pedicle and 2 mm below the vertebral artery sulcus. The project-point of the entry pathway on the atlas posterior arch was considered to be the entry point. Forty-eight dry atlas specimens were used to measure the following relevant anatomic data with an electronic caliper: the distance between the entry point and the posterior margin of the lateral mass (L1), the height of atlas pedicle at the entry point (L2), the vertical distance between the entry point and the inferior articular facet of the lateral mass (L3), the mass height at the entry point (L4), the mass width at the entry point (L5), the width of the atlas pedicle at the entry point (L6), the thickness of the pedicle under the vertebral artery sulcus at the entry pathway (H1). To research the method of the pedicle screw fixation, 12 fresh-frozen adult atlas specimens were adopted to simulate the fixation of the pedicle screw. The thickness of the bone substance of vertebral artery sulcus on both the left and the right sides of the pathway was grinded into 3 types: 1.5 mm and 2.5 mm, 1.5 mm and 4.0 mm, 2.5 mm and 4.0 mm, and each type had four specimens. The entry pathway - was confirmed by the intersection line of two transverse sections that went through the lateral one third of atlas pedicle and 2 mm below the vertebral artery sulcus. RESULTS: On the left side, L1 was (5.79 +/- 1.24) mm, L2 (4.55 +/- 1.29) mm, L3 (5.12 +/- 1.06) mm, L4 (12.43 +/- 1.01) mm, L5 (12.66 +/- 1.37) mm, L6 (7.86 +/- 0.77) mm, and H1 (4.11 +/- 1.25) mm. On the right side, L1 was (5.81 +/- 1.26) mm, L2 (4.49 +/- 1.22) mm, L3 (5.15 +/- 1.05) mm, L4 (12.49 +/- 0.98) mm, L5 (12.65 +/- 1.38) mm, L6 (7.84 +/- 0.78) mm, and H1 (4.13 +/- 1.29) mm. There was no significant difference between the two sides (P > 0.05). After simulation of inserting screws, no screw in the specimens was found to break the bone substance in the sulcus of vertebral artery. Conclusion For the pedicle screw fixation of those patients whose atlas posterior arches are not high enough, we might partly drill through or beyond the atlas posterior arch. The entry point should be ascertained by preoperative 3D-CT reconstruction and intra-operative exploration.