Residual sagittal motion after lumbar fusion - A finite element analysis with implications on radiographic flexion-extension criteria
Residual sagittal motion after lumbar fusion - A finite element analysis with implications on radiographic flexion-extension criteria
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DOI：
10.1097/01.brs.0000255201.74795.20
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发表时间：
2007-02-15
期刊：
影响因子：
3
通讯作者：
Garfin, Steven R.
中科院分区：
文献类型：
--
作者：
Bono, Christopher M.;Khandha, Ashutosh;Garfin, Steven R.
研究设计。腰椎融合模型的有限元分析。量化不同类型和程度腰椎融合完成后的残留矢状角运动，以便更好地理解当前解读屈伸x线片以评估融合的有效性。背景资料摘要。椎体间角运动从0到5不等，使用屈伸x线片推荐的椎体融合阈值标准不同。尽管存在这种广泛的差异和缺乏统一的共识，但据作者所知，这些标准的有效性此前尚未进行过生物力学评估。为了研究这个问题，作者试图用有限元模型测试各种类型的模拟愈合的、无器械的腰椎融合体，以确定生理应力下残余角运动的量。建立了完整成人L3-L4运动节段的三维非线性有限元模型。使用该模型模拟了四种融合类型，包括前路腰椎椎体间融合（ALIF）、后路腰椎椎体间融合（PLIF）、横突间融合和棘突间融合。还表示了融合完整性的变化。对于ALIF和PLIF，这包括在后部或前部椎间盘间隙75%、50%或25%内进行实性桥接骨的测试。此外，PLIF还通过单侧或双侧面部切除术进行测试，以模拟常用的手术技术。横突间融合的变化包括单侧或双侧桥骨伴或不伴内侧关节间部融合。只测试了一种愈合的、坚固的棘突间融合的情况。对完整模型和所有融合模型施加10.6 nm的屈伸力矩。角偏转以度为单位记录。记录了大范围的矢状角运动。对于ALIF，评分范围从0.8（完全100%融合）到3.3（后部25%椎间盘间隙的牢固融合）。对于PLIF，数字变化更大，从0.7（完全，100%融合）到6.9（后25%椎间盘间隙实融合，双侧面切除术）。对于横突间融合，运动最小的是稳固的双侧融合，内侧愈合到parts (2.0)；运动最大的是单侧牢固融合，没有内侧愈合（6.0）。棘突间融合仅允许1.9°的运动。模拟腰椎融合术在生理可比力矩下的残余屈伸活动量（可能是由骨固有弹性所允许的）随融合术类型的不同而不同，更重要的是，随融合术完整性的不同而不同。目前的研究记录了几种模拟腰椎融合术后的矢状角运动范围，这些模拟腰椎融合术似乎与先前使用屈伸x线片进行实性融合术的放射学标准有相当大的重叠。然而，这也表明，在某些情况下，稳固但不完整的融合可能允许运动大大大于5，这超出了先前公布的最宽松的阈值标准。
Study Design. Finite element analysis of a lumbar fusion model.Objectives. To quantify residual sagittal angular motion following various types and levels of completeness of lumbar fusion in order to understand better the validity of current recommendations for interpreting flexion-extension radiographs to assess fusion.Summary of Background Data. Recommended threshold criteria for solid fusion using flexion-extension radiographs have varied from 0 to 5 of angular motion between vertebrae. Notwithstanding this wide variation and lack of uniform consensus, the validity of these criteria has not been previously biomechanically assessed to the authors' knowledge. To investigate this issue, the authors sought to test various types of simulated healed, noninstrumented lumbar fusions using finite element modeling to determine the amount of residual angular motion under physiologic stresses.Methods. A validated 3-dimensional, nonlinear finite element model of an intact adult human L3-L4 motion segment was developed. Four fusion types were simulated using this model, including anterior lumbar interbody fusion (ALIF), posterior lumbar interbody fusion (PLIF), intertransverse process fusion, and interspinous process fusion. Variations of completeness of fusion were also represented. For ALIF and PLIF, this included tests of solid bridging bone within the posterior or anterior 75%, 50%, or 25% disc space. In addition, PLIF was also tested with either a unilateral or bilateral facetectomy to simulate commonly used surgical techniques. Variations of intertransverse process fusion included unilateral or bilateral bridging bone with or without medial fusion to the pars interarticularis. Only 1 scenario of a healed, solid interspinous process fusion was tested. The intact model and all fusion models were stressed with 10.6-Nm flexion and extension moments. The angular deflections were recorded in degrees.Results. A wide range of sagittal angular motion was recorded. For ALIF, this ranged from 0.8 (complete, 100% fusion) to 3.3 (solid fusion of the posterior 25% disc space). For PLIF, the numbers were more varied, ranging from 0.7 (complete, 100% fusion) to 6.9 (solid fusion of posterior 25% disc space with bilateral facetectomy). For intertransverse process fusion, the least motion was with a solid bilateral fusion, with medial healing to the pars (2.0); the greatest motion was found with a solid unilateral fusion without medial healing (6.0). Interspinous process fusion allowed only 1.9 of motion.Conclusions. The amount of residual flexion-extension motion with simulated lumbar fusions (presumably allowed by the bone's inherent elasticity) under physiologically comparable moments varies with fusion type and, more substantially, with varying amounts of completeness. The current study documents a range of sagittal angular motion after several types of simulated lumbar fusion that appear to have considerable overlap with previously purported radiographic criteria for solid fusion using flexion-extension radiographs. However, it also suggests the possibility that some scenarios of solid, yet incomplete, fusion may allow motion that is substantially greater than 5, which is beyond the most liberal of previously published threshold criteria.