非融合棘突间固定器不同棘突间撑开高度对植入节段椎间盘压力分布的影响

背景：腰椎退变性疾病目前的非融合内固定特别是棘突间固定理论上可以保留有益活动,在缓解疼痛的同时预防邻近节段退变。 目的：测量棘突间不同的撑开程度情况下节段椎间盘负荷分担及应力分布情况。 方法：新鲜成人腰椎标本L_2~5,采用电子万能实验机模拟腰椎前屈、中立、后伸运动负荷。实验分为7组：正常脊柱组,形状记忆合金棘突间固定器支撑高度10,12,14,16,18,20 mm组。 结果与结论：支撑高度为10 mm的形状记忆合金棘突间固定器对植入节段椎间盘的压力分布无显著性影响;支撑高度为12 mm的形状记忆合金棘突间固定器在过伸时可分担46%的椎间盘后纤维环负荷(P < 0.05);支撑高度为14 mm的形状记忆合金棘突间固定器可维持植入节段的轻度前屈,在过伸时可分担约47%的后环负荷(P < 0.05),但后伸时会增大前环的负荷,当支撑高度远大于植入节段中立位时的棘突间高度时,屈伸活动时,后环的负荷显著降低的同时,前环负荷可增大达400%。提示支撑高度等于或略大于中立位棘突间高度的非融合棘突间固定器可分担椎间盘负荷并使椎间盘应力更均匀分布;但支撑高度过大会明显增大前环的负荷,如果用于神经源性间歇性跛行患者的椎间孔撑开,可能会加快椎间盘的退变。

Effects of a new shape-memory alloy interspinous process device on the pressure distribution of implanted intervertebral disc segment

BACKGROUND: The degeneration of the intervertebral disc and zygapophyseal joints (facet joint) is the main cause of degenerative lumbar stenosis with the clinical outcomes including chronic low back pain and neurogenic intermittent claudication. Dynamic stabilization devices, especially non-fusion interspinous process stabilization devices (IPD), are noteworthy in saving segmental movement, showing faster recovery and rehabilitation without increasing the degeneration of adjacent segments. OBJECTIVE:To compare and quantify the disc pressure to understand the likelihood of accelerated disc degeneration in the implanted level to optimize the usage of the implant. METHODS:Six cadaver lumbar specimens (L_2–5) were loaded in flexion, neutral, and extension. A pressure measuring film measured the disc load during each of the three positions at each L_3-4 disc level. The implant with different spacer height including 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm was placed at L₃-L₄ by turns, and the pressure measurements were repeated. RESULTS AND CONCLUSION: The IPD with 10 mm spacer height could not significantly share the disc load. The 12 mm implant significant shared posterior annulus load only in extension. The 14 mm implant decreased the stress in posterior annulus and nucleus in extension and neutral but slightly increased the anterior annulus load. Though the 16 mm-20 mm implants decreased the posterior annulus’ stress significantly, the anterior annulus load was increased about 400% in aforementioned three positions. Different distraction degrees of interspinous process may lead to different disc load distribution, the implant would be not appropriate to those serious spinal stenosis because of the contradictions that though the over distraction can decrease the posterior annulus load and distract the intervertebral foramina, it will lead to an acceleration of disc degeneration by the excessive load increasing in anterior annulus.