臼轨式椎弓根钉非融合动态固定腰椎的稳定性评价

Evaluation of the biomechanical stability of lumbar dynamicly fixed by socket track pedicle screws

目的探讨使用臼轨式椎弓根钉单节段动态固定减压失稳腰椎的稳定性效果。方法臼轨式椎弓根钉为钛合金材质，螺钉可万向活动，钉座下口约束螺钉的活动范围；螺钉矢状面活动≤18°，水平面活动≤8°。选取6具猪腰椎标本（L1-5），每具标本按手术顺序依次制成完整脊柱（脊柱结构正常，置入4枚臼轨式椎弓根钉）、动态固定1（L3-4全椎板被切除，保留4枚臼轨式椎弓根钉，双侧上连接棒并锁定）、动态固定2（L3-4全椎板及双侧小关节被切除，保留4枚臼轨式椎弓根钉，双侧上连接棒并锁定）、减压失稳（全椎板及双侧小关节被切除，保留4枚臼轨式椎弓根钉，拆除双侧连接棒）、混合固定（L3-4全椎板及双侧小关节被切除，保留2枚臼轨式椎弓根钉，另2枚为单向椎弓根钉，双侧上连接棒并锁定）5组试验模型，并在4．018Nm的纯力偶矩作用下分别进行屈伸、侧弯、旋转活动，检测其运动范围。结果L3-4运动范围，在动态固定1、2和混合固定后，在前屈、后伸及侧弯时，各组运动范围均较完整脊柱组（前屈、后伸及侧弯分别为1．84°±0．75°、1．55°±0．34°、2．2°±1．07°）明显减少，动态固定1组分别为0．71°±0．39°、0．46°±0．18°、0．85°±0．66°，动态固定2组分别为0．79。±0．43。、0．71°±0．20°、1．17°±0．48°，混合固定组分别为0．63°±0．50°、0．37°±0．19°、0．54°±0．60°；在旋转时运动范围，动态固定1组为1．50°±0．64°，动态固定2组为1．85°±0．67°，混合固定组为1．22°±0．36°，均较完整脊柱旋转运动范围（2．06°±0．76°）减少。三组内固定比较，在后伸、旋转方向，动态固定2组运动范围较动态固定1组增加；在后伸、侧弯、旋转方向，混合固定组较动态固定2组运动范围减少，两者比较差异均有统计学意义。结论在腰椎单节段全椎板及双侧小关节完整切除减压术后，采用臼轨式椎弓根钉进行动态固定，可以降低标本在屈伸、侧弯和旋转方向的运动范围，提供即刻的稳定性。

Objective To investigate the stability of lumbar single-level dynamicly fixed by socket track pedicle screws after decompression. Methods Socket track pedicle screws are made of titanium-alloy, swing like universal screw within the scope of 18° in the sagittal plane and 8° in the horizontal plane. Motion constraints were due to the hole which the screw goes through. Six pig spines （L4-5） were tested by applying a pure moment of 4.018 Nm in 3 directions of loading. The range of motion （ROM） of the following groups underwent different surgical procedures was measured： （1） intact; （2） dynamic fixation 1 （decompression by total laminectomy and instrumentation with socket track pedicle screws）; （3） dynamic fixation 2 （decompression by total laminectomy and bilateral facetectomy while instrumentation with socket track pedicle screws）; （4） instability resulted from decompression （decompression by total laminectomy plus bilateral facetectomy without any rod）; （5） hybrid fixation （decompression by total laminectomy and bilateral facetectomy while instrumentation with 2 socket track pedicle screws connected with 2 unilateral pedicle screws ）. Results Compared with the intact specimens （in flexion, extension, lateral bending and rotation, corresponding angular displacements were 1.84°±0.75°, 1.55°±0.34°, 2.2°±1.07°, 2.06°±0.76° respectively）, the ROM of segment L3, 4 of each group were significantly restricted except for axial rotation. In flexion, extension and lateral bending, the ROM was reduced to 0.71°±0.39°, 0.46°±0.18°, 0.85°±0.66° in dynamic fixation 1 group; 0.79°±0.43°, 0.71°±0.20°, 1.17°±0.48° in dynamic fixation 2 group and 0.630±0.50°, 0.37°±0.19°, 0.540±0.60° in hybrid fixation group. The rotation ROM of dynamic fixation 1 group and hybrid fixation group were decreased to 1.50°±0.64° and 1.22°±0.36°, whereas the ROM of dynamic fixation 2 had a non-significant reduction to 1.85°±0.67°. The extension and rotation ROM of dynamic fixation 2 increased significantly comparing to dynamic fixation 1 group; the extension, lateral bending and axial rotation ROM of hybrid fixation group were reduced comparing to the state of dynamic fixation 2 group. Conclusion The dynamic instrumentation of single-level lumbar spine with socket track pedicle screws eould offer stability in all directions. The flexion, extension, lateral bending and rotation ROM of spine with dynamic instrumentation after total laminectomy and bilateral faceteetomy could be reduced.