Blagg Stuart E, Don Angus S, Robertson Peter A
Department of Orthopaedic Surgery, Auckland Hospital, Auckland, New Zealand.
J Spinal Disord Tech. 2009 Jun;22(4):233-9. doi: 10.1097/BSD.0b013e31817ff95a.
Anatomic study of C1 osteology using computerized tomography.
To define the anatomy of the C1 lateral mass and make recommendations for optimal entry point and screw placement at C1.
C1 lateral mass screw fixation is a reliable biomechanical technique that gives equivalent stability to that of Magerl transarticular screw fixation combined with posterior wiring for C1-C2 fusion. Use of a lateral mass screw allows alternative stabilization constructs to the transarticular technique when C2 vertebral artery anatomy is unfavorable. Because the vertebral artery travels lateral to the lateral mass, then crosses medially over the C1 neural arch, it is at risk during instrumentation. Medially, the cord and canal contents are at risk. While the anatomy of the C1 vertebra and lateral mass is well known, specific definition of ideal entry points, screw pathway direction, and dimensions of screws requires further clarification to enable a clinically safe surgical technique.
Fifty consecutive patients underwent computerized tomography scans of their cervical spine. Using calibrated scans, measurements were taken to give the average dimensions of the C1 vertebra with a view for insertion of lateral mass screws beneath the posterior arch. The range of anatomic dimensions was examined to assess risk of vertebral artery damage in this population.
The average length of screw within the lateral mass is 17.9 mm with 21.5 mm of screw posterior to the lateral mass, necessary to allow rod placement posteriorly. The safest entry point was directly beneath the medial edge of the posterior arch/lamina where it joins the lateral mass. The ideal direction of screw angulation in the sagittal plane was parallel to the posterior arch of C1. In the medial lateral plane, direct anterior placement could be used, but the lateral mass will tolerate 20 degrees of medial angulation from this starting point. The average distance between the vertebral artery foramen laterally and the screw pathway was 8.8 mm using these landmarks, and 5.8 mm from the medial aspect of the lateral mass. The range of anatomic variation was such that 9 lateral masses had a vertebral artery foramen to screw distance of only 3 mm. The vertebral artery was not at risk when these anatomic landmarks were used.
C1 lateral mass screws are best placed beneath the posterior arch, parallel with the arch in the sagittal plan. The entry point is the medial border of the neural arch at its junction with the lateral mass. Straight ahead screw direction is safe in the axial plane, but up to 20 degrees of medial angulation will increase the safety margin from the vertebral artery foramen, and this technique avoids vertebral artery damage and optimizes lateral mass screw purchase. We suggest that this is the preferred method of entry into the lateral mass of C1.
使用计算机断层扫描对C1骨学进行解剖学研究。
明确C1侧块的解剖结构，并为C1的最佳进针点和螺钉置入提出建议。
C1侧块螺钉固定是一种可靠的生物力学技术，其稳定性与用于C1-C2融合的马格勒经关节螺钉固定联合后路钢丝固定相当。当C2椎动脉解剖结构不利时，使用侧块螺钉可提供与经关节技术不同的稳定结构。由于椎动脉在侧块外侧走行，然后在内侧越过C1神经弓，因此在器械操作过程中存在风险。在内侧，脊髓和椎管内容物也有风险。虽然C1椎体和侧块的解剖结构是众所周知的，但理想进针点、螺钉路径方向和螺钉尺寸的具体定义需要进一步明确，以实现临床安全的手术技术。
连续50例患者接受了颈椎计算机断层扫描。使用校准扫描进行测量，以得出C1椎体的平均尺寸，以便在后弓下方置入侧块螺钉。检查解剖尺寸范围，以评估该人群中椎动脉损伤的风险。
侧块内螺钉的平均长度为17.9 mm，侧块后方的螺钉长度为21.5 mm，这是在后方放置棒所必需的。最安全的进针点是后弓/椎板内侧边缘与侧块交界处的正下方。矢状面内螺钉的理想成角方向与C1后弓平行。在内外侧平面，可采用直接向前置入，但从该起始点起，侧块可耐受20度的内侧成角。使用这些标志，外侧椎动脉孔与螺钉路径之间的平均距离为8.8 mm，距侧块内侧缘5.8 mm。解剖变异范围使得9个侧块的椎动脉孔与螺钉的距离仅为3 mm。使用这些解剖标志时，椎动脉没有风险。
C1侧块螺钉最好置于后弓下方，在矢状面与后弓平行。进针点是神经弓与侧块交界处的内侧边界。在轴位平面，直接向前的螺钉方向是安全的，但内侧成角达20度将增加与椎动脉孔的安全 margin，并且该技术可避免椎动脉损伤并优化侧块螺钉的把持。我们建议这是进入C1侧块的首选方法。
