Liu Po-Yi, Lai Po-Liang, Lin Chun-Li
Department of Biomedical Engineering, National Yang-Ming University, No.155, Sec. 2, Linong St., Beitou Dist., Taipei City 11221, Taiwan; Department of Orthopedic Surgery, Bone and Joint Research Center, Chang Gung Memorial Hospital at Linkou, College of Medicine, Chang Gung University, No. 5, Fuxing St., Guishan Dist., Taoyuan City 33305, Taiwan.
Department of Orthopedic Surgery, Bone and Joint Research Center, Chang Gung Memorial Hospital at Linkou, College of Medicine, Chang Gung University, No. 5, Fuxing St., Guishan Dist., Taoyuan City 33305, Taiwan.
Clin Biomech (Bristol). 2019 Dec;70:23-30. doi: 10.1016/j.clinbiomech.2019.06.003. Epub 2019 Jul 10.
Pedicle screw based spinal fixation systems have been widely used for treating a variety of spinal diseases. The retentive force is an important factor that determines structural stability. The screw tulip design and the magnitude of nut tightening torque influence the retentive force. This study investigated the influences of varied tilt angles between the shaft-rod interface and varied nut tightening torques on the retentive force of the monoaxial, polyaxial, and uniplanar screws.
Three types of tulip constructs were biomechanically tested. Two parameters that affect the retentive force include the tilt angle and the nut tightening torque. The retentive force was investigated by an axial gripping capacity test and axial torque gripping capacity test.
Among all combinations of screw designs and tilt angles, the 12 Nm nut tightening torque offered a greater retentive force than the 8 Nm, except for monoaxial screws with a 0 degree tilt angle. For monoaxial screws, the retentive force was negatively correlated with increasing tilt angles. For polyaxial and uniplanar screws, the retentive forces remained constant with increasing tilt angles.
In monoaxial screws, when the axis of the shaft isn't perpendicular to the axis of the rod, a gap is formed between the tulip-rod interface. This results in a decreased retentive force. In polyaxial and uniplanar screws, the contact surfaces were the same in different tilt angles, therefore, the retentive force remained constant, which was attributed to the adjustable tulips always being perpendicular to the axis of the rods.
基于椎弓根螺钉的脊柱固定系统已广泛用于治疗各种脊柱疾病。保持力是决定结构稳定性的重要因素。螺钉的球茎设计和螺母拧紧扭矩的大小会影响保持力。本研究调查了轴-杆界面之间不同倾斜角度和不同螺母拧紧扭矩对单轴、多轴和单平面螺钉保持力的影响。
对三种类型的球茎结构进行生物力学测试。影响保持力的两个参数包括倾斜角度和螺母拧紧扭矩。通过轴向夹紧能力测试和轴向扭矩夹紧能力测试来研究保持力。
在所有螺钉设计和倾斜角度的组合中，除了倾斜角度为0度的单轴螺钉外，12 Nm的螺母拧紧扭矩比8 Nm提供了更大的保持力。对于单轴螺钉，保持力与倾斜角度的增加呈负相关。对于多轴和单平面螺钉，随着倾斜角度的增加，保持力保持不变。
在单轴螺钉中，当轴的轴线不垂直于杆的轴线时，球茎-杆界面之间会形成间隙。这导致保持力降低。在多轴和单平面螺钉中，不同倾斜角度下的接触面相同，因此保持力保持不变，这归因于可调节球茎始终垂直于杆的轴线。
