1 南方医科大学南方医院脊柱骨科 2 南方医科大学第一临床医学院附属郴州医院（郴州市第一人民医院）脊柱外科;2.南方医科大学南方医院脊柱骨科 广州市;3.南方医科大学第一临床医学院附属郴州医院郴州市第一人民医院脊柱外科
1.Department of Spinal Surgery, Nanfang Hospital，Southern Medical University 2.Department of Spine Surgery, Affiliated Chenzhou Hospital，The first School of clinical Medicine，Southern Medical University（The First People’s Hospital of Chenzhou）;2.Department of Spinal Surgery,Nanfang Hospital,Southern Medical University;3.Department of Spine Surgery,Affiliated Chenzhou Hospital,The first School of clinical Medicine,Southern Medical UniversityThe First People’s Hospital of Chenzhou
目的：探讨动态固定（转动钉、滑动钉）对寰枢关节稳定性的影响。 方法：用6具新鲜成人枕骨（Oc）-颈椎（C4）节段进行测试，模拟以下手术及固定状态：①完整状态；②损伤状态：枢椎齿状突II型骨折；③坚强固定：寰枢椎均采用普通椎弓根螺钉固定，直径3.5mm钛棒连接；④转动钉固定：寰椎采用2枚可转动螺钉固定；⑤滑动钉固定：寰椎采用2枚可滑动螺钉固定。采用重复测量的实验设计，在完整、损伤和不同的固定状态下，通过脊柱试验机对标本分别施加1.5Nm的前屈/后伸、左/右侧弯和左/右轴向旋转的纯力偶矩。三维运动系统测量寰枢椎运动，分析比较固定节段角度运动范围（ROM）和中性区（NZ）。 结果：损伤状态在前屈、后伸、侧弯和旋转方向上均显著增加了寰枢关节的运动范围，产生了寰枢关节不稳。在前屈、后伸、侧弯和旋转方向上，坚强固定和动态固定后ROM均显著减小。与坚强固定比较，动态固定仅在侧弯方向上ROM较大（P转动钉=0.024，P滑动钉=0.001）。动态固定显著减小了在屈伸、侧弯和旋转上的NZ（P＜0.05），且与坚强固定之间的差异无显著性。 结论：本研究证实寰枢关节动态固定后，在前屈、后伸和旋转方向上的稳定性与坚强固定相当，但在侧弯方向上较弱。动态固定能够维持寰枢关节的相对稳定。
Objectives: To evaluate the influence of dynamic pedicle screws on the stability of the Atlantoaxial Joint. Methods: A series of in vitro biomechanical tests were performed using six fresh adult cervical spines (occipital bone-C4 segment) to simulate different conditions in surgery including the (1) intact state; (2) injury state: type II odontoid process fracture; (3) rotating pedicle screw: two rotating pedicle screws were bilaterally inserted in the Atlas pedicle and the Axis was fixed by two ordinary polyaxial pedicle screws, which were connected by a titanium rod with a diameter of 3.5 mm; (4) sliding pedicle screw: two sliding pedicle screws were bilaterally reinserted into the Atlas pedicle with other internal fixation components unchanged in comparison with (3);（5）rigid fixation：Atlas and the Axis were fixed by four ordinary polyaxial pedicle screws, which were connected by a titanium rod with a diameter of 3.5 mm. Biomechanical studies of samples were performed under intact, injury and various fixation statements using a spinal testing machine, while applying a constant moment of 1.5 Nm in flexion-extension, left-right lateral bending, and left-right axial rotation directions. A repeated measurement design was employed in all tests. Movement were measured consecutively by an Optotrak Certus 3D measurement system in order to analyze the range of motion (ROM) and neutral zone (NZ) of Atlantoaxial Joint. Results: In the atlantoaxial joint, ROM in C1 and C2 of the injury state caused by odontoid process fracture was significantly larger than the intact state in flexion, extension, lateral bending and rotation (P<0.05). ROM of fixation segments was significantly reduced in flexion, extension, lateral bending and rotation directions when rotating and sliding pedicle screw fixations were used (P<0.05), compared with the intact state. A significant increase in ROM for rotating and sliding pedicle screw fixations in lateral bending was obtained, compared with rigid fixation (Protating screws=0.024, Psliding screws=0.001). NZs of fixation segments for rigid fixation, rotating pedicle screw fixation, and sliding pedicle screw fixation were significantly reduced (P<0.05). There were no significant differences among these fixations (P>0.05). Conclusions: In the atlantoaxial joint, stability of using two rotating screws or sliding screws for fixation was comparable to rigid fixation in flexion, extension and rotation directions, but was weaker in the lateral bending direction. Dynamic screws fixation can maintain the relative stability of the atlantoaxial joint.