Department of Orthopaedic Surgery, University of Pennsylvania, Philadelphia, PA, USA.
Spine (Phila Pa 1976). 2011 Oct 1;36(21):1765-71. doi: 10.1097/BRS.0b013e318216752f.
Biomechanics of human intervertebral discs before and after nucleotomy.
To noninvasively quantify the effect of nucleotomy on internal strains under axial compression in flexion, neutral, and extension positions, and to determine whether the change in strains depended on degeneration.
Herniation and nucleotomy may accelerate the progression of disc degeneration. Removal of nucleus pulposus (NP) tissue has resulted in altered disc mechanics in vitro, including a decrease in internal pressure and an increase in the deformations at physiologically relevant strains. We recently presented a technique to quantify internal disc strains using magnetic resonance imaging (MRI).
Degeneration was quantitatively assessed by the T1ρ relaxation time in the NP. Samples were prepared from human levels L3-L4 and/or L4-L5. A 1000-N compressive load was applied while in the magnetic resonance scanner. Nucleotomy was performed by removing 2 g of NP through the posterior-lateral annulus fibrosus (AF). The discs were rehydrated, reimaged, and retested. The analyzed parameters include axial deformation, AF radial bulge, and strains. RESULTS.: The axial deformation was more compressive after nucleotomy. In the neutral position, the axial deformation after nucleotomy correlated with degeneration (as quantified by T1ρ in the NP), with minimal alteration in nondegenerated discs. Nucleotomy altered the radial displacements and strains in the neutral position, such that the inner AF radial bulge decreased and the radial strains were more tensile in the lateral AF and less tensile in the posterior AF. In the bending loading positions the radial strains were not affected by nucleotomy.
Nucleotomy alters the internal radial and axial AF strains in the neutral position, which may leave the AF vulnerable to damage and microfractures. In bending, the effects of nucleotomy were minimal, likely due to more of the applied load being directed over the AF. Some of the nucleotomy effects are modulated by degeneration, where the mechanical effect of nucleotomy was magnified in degenerated discs and may further induce mechanical damage and degeneration.
核切术前、后人类椎间盘的生物力学。
非侵入性地定量评估核切术在屈曲、中立和伸展位轴向压缩下对内部分应变的影响，并确定应变的变化是否取决于退变。
椎间盘突出和核切术可能加速椎间盘退变的进展。髓核组织的切除导致体外椎间盘力学的改变，包括内部压力降低和生理相关应变下变形增加。我们最近提出了一种使用磁共振成像（MRI）定量评估椎间盘内应变的技术。
通过 NP 的 T1ρ弛豫时间定量评估退变。样本取自人类 L3-L4 和/或 L4-L5 水平。在磁共振扫描仪中施加 1000-N 的压缩载荷。通过后外侧纤维环（AF）切除 2 克 NP 进行核切术。将椎间盘重新水合、重新成像并重新测试。分析的参数包括轴向变形、AF 径向膨出和应变。
核切术后轴向变形更具压缩性。在中立位，核切术后的轴向变形与退变相关（如 NP 中的 T1ρ 定量），非退变椎间盘的变化最小。核切术改变了中立位的径向位移和应变，使得内 AF 径向膨出减少，外侧 AF 的径向应变更具拉伸性，而后侧 AF 的拉伸性更小。在弯曲加载位置，核切术对径向应变没有影响。
核切术改变了中立位的 AF 内、轴向应变，这可能使 AF 容易受到损伤和微裂缝的影响。在弯曲时，核切术的影响最小，可能是因为更多的施加载荷在 AF 上。核切术的一些影响受到退变的调节，在退变的椎间盘中，核切术的力学效应被放大，可能进一步诱导力学损伤和退变。
