Department of Biomedical Engineering, Faculty of Environment and Life, Beijing University of Technology, Beijing, China.
Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education, Beijing University of Technology, Beijing, China.
Comput Methods Programs Biomed. 2023 Aug;238:107625. doi: 10.1016/j.cmpb.2023.107625. Epub 2023 May 26.
Screw loosening remains a prominent problem for osteoporotic patients undergoing pedicle screw fixation surgeries but its underlying mechanisms are not fully understood. This study sought to examine the interactive effect of craniocaudal or axial cyclic loading (toggling) and osteoporosis on screw fixation.
QCT-based finite element models of normal (n = 7; vBMD = 156 ± 13 mg/cm) and osteoporotic vertebrae (n = 7; vBMD = 72 ± 6 mg/cm) were inserted with pedicle screws and loaded with or without craniocaudal toggling. Among them, a representative normal vertebra (age: 55; BMD: 140 mg/cm) and an osteoporotic vertebra (age: 64; BMD: 79 mg/cm) were also loaded with or without axial toggling. The individual and interactive effects of craniocaudal toggling and osteoporosis on screw fixation strength (the force when the pull-up displacement of the screw head reached 1 mm) and bone tissue failure (characterized by equivalent plastic strain) were examined by repeated measure ANOVA.
A significant interactive effect between craniocaudal toggling and osteoporosis on screw fixation strength was detected (p = 0.008). Specifically, craniocaudal toggling led to a marked decrease in the fixation strength (68%, p < 0.05) and stiffness (83%, p < 0.05) only in the osteoporotic vertebrae but had no effect on screw fixation strength and stiffness of the normal vertebrae (p > 0.05). Likewise, most of the bone tissues around the screw in the osteoporotic vertebrae yielded following craniocaudal toggling whereas this result was not seen in the normal vertebrae. The axial toggling had no significant effect on bone tissue failure as well as pedicle screw fixation in normal or osteoporotic vertebrae.
Craniocaudal toggling substantially reduces the screw fixation strength of the osteoporotic vertebrae by progressively increasing tissue failure around the screw, and therefore may contribute to the higher rates of screw loosening in osteoporotic compared to normal patients, whereas axial toggling is not a risk factor for pedicle screw loosening in normal or osteoporotic patients.
螺钉松动仍然是骨质疏松症患者接受椎弓根螺钉固定手术的一个突出问题，但其潜在机制尚不完全清楚。本研究旨在探讨颅尾或轴向循环加载（摆动）与骨质疏松症对螺钉固定的交互作用。
采用基于 QCT 的正常（n=7；vBMD=156±13mg/cm）和骨质疏松椎骨（n=7；vBMD=72±6mg/cm）有限元模型，在椎弓根螺钉上插入椎骨，并在有无颅尾摆动的情况下进行加载。其中，一个有代表性的正常椎体（年龄：55；BMD：140mg/cm）和一个骨质疏松椎体（年龄：64；BMD：79mg/cm）也在有无轴向摆动的情况下进行了加载。通过重复测量方差分析，检查颅尾摆动和骨质疏松症对螺钉固定强度（当螺钉头的拔出位移达到 1mm 时的拉力）和骨组织失效（以等效塑性应变为特征）的单独和交互影响。
发现颅尾摆动和骨质疏松症对螺钉固定强度有显著的交互作用（p=0.008）。具体来说，颅尾摆动仅导致骨质疏松椎骨的固定强度（68%，p<0.05）和刚度（83%，p<0.05）明显下降，但对正常椎骨的螺钉固定强度和刚度没有影响（p>0.05）。同样，在骨质疏松椎骨中，大多数螺钉周围的骨组织在颅尾摆动后发生屈服，而在正常椎骨中则没有这种情况。轴向摆动对正常或骨质疏松椎骨的骨组织失效以及椎弓根螺钉固定均无显著影响。
颅尾摆动通过逐渐增加螺钉周围的组织失效，显著降低骨质疏松椎骨的螺钉固定强度，因此可能导致骨质疏松症患者螺钉松动的发生率高于正常患者，而轴向摆动不是正常或骨质疏松患者椎弓根螺钉松动的危险因素。
