Luo Jin, Annesley-Williams Deborah J, Adams Michael A, Dolan Patricia
School of Applied Sciences, London South Bank University, 103 Borough Rd, London SE1 0AA, UK.
Department of Neuroradiology, Nottingham University Hospitals NHS Trust, Queen's Medical Centre, Derby Rd, Nottingham NG7 2UH, UK.
Spine J. 2017 Jun;17(6):863-874. doi: 10.1016/j.spinee.2017.01.013. Epub 2017 Feb 3.
Spinal injuries and surgery may have important effects on neighboring spinal levels, but previous investigations of adjacent-level biomechanics have produced conflicting results. We use "stress profilometry" and noncontact strain measurements to investigate thoroughly this long-standing problem.
This study aimed to determine how vertebral fracture and vertebroplasty affect compressive load-sharing and vertebral deformations at adjacent spinal levels.
We conducted mechanical experiments on cadaver spines.
Twenty-eight cadaveric spine specimens, comprising three thoracolumbar vertebrae and the intervening discs and ligaments, were dissected from fourteen cadavers aged 67-92 years. A needle-mounted pressure transducer was used to measure the distribution of compressive stress across the anteroposterior diameter of both intervertebral discs. "Stress profiles" were analyzed to quantify intradiscal pressure (IDP) and concentrations of compressive stress in the anterior and posterior annulus. Summation of stresses over discrete areas yielded the compressive force acting on the anterior and posterior halves of each vertebral body, and the compressive force resisted by the neural arch. Creep deformations of vertebral bodies under load were measured using an optical MacReflex system. All measurements were repeated following compressive injury to one of the three vertebrae, and again after the injury had been treated by vertebroplasty. The study was funded by a grant from Action Medical Research, UK ($143,230). Authors of this study have no conflicts of interest to disclose.
Injury usually involved endplate fracture, often combined with deformation of the anterior cortex, so that the affected vertebral body developed slight anterior wedging. Injury reduced IDP at the affected level, to an average 47% of pre-fracture values (p<.001), and transferred compressive load-bearing from nucleus to annulus, and also from disc to neural arch. Similar but reduced effects were seen at adjacent (non-fractured) levels, where mean IDP was reduced to 73% of baseline values (p<.001). Vertebroplasty partially reversed these changes, increasing mean IDP to 76% and 81% of baseline values at fractured and adjacent levels, respectively. Injury also increased creep deformation of the vertebral body under load, especially in the anterior region where a 14-fold increase was observed at the fractured level and a threefold increase was observed at the adjacent level. Vertebroplasty also reversed these changes, reducing deformation of the anterior vertebral body (compared with post-fracture values) by 62% at the fractured level, and by 52% at the adjacent level.
Vertebral fracture adversely affects compressive load-sharing and increases vertebral deformations at both fractured and adjacent levels. All effects can be partially reversed by vertebroplasty.
脊柱损伤与手术可能会对相邻脊柱节段产生重要影响，但以往关于相邻节段生物力学的研究结果相互矛盾。我们使用“应力轮廓测量法”和非接触应变测量来深入研究这一长期存在的问题。
本研究旨在确定椎体骨折和椎体成形术如何影响相邻脊柱节段的压缩载荷分担及椎体变形。
我们对尸体脊柱进行了力学实验。
从14具年龄在67 - 92岁的尸体上解剖获取28个尸体脊柱标本，每个标本包含三个胸腰段椎体以及其间的椎间盘和韧带。使用安装在针上的压力传感器测量两个椎间盘前后径上的压缩应力分布。分析“应力轮廓”以量化椎间盘内压力（IDP）以及前、后纤维环中的压缩应力集中情况。对离散区域的应力求和得出作用于每个椎体前半部分和后半部分的压缩力，以及神经弓所抵抗的压缩力。使用光学MacReflex系统测量加载下椎体的蠕变变形。在对三个椎体中的一个进行压缩损伤后，以及在损伤通过椎体成形术治疗后，重复所有测量。本研究由英国医学研究行动组织提供的一笔143,230美元的资助。本研究的作者不存在利益冲突需要披露。
损伤通常涉及终板骨折，常伴有前皮质变形，使得受影响的椎体出现轻微的前楔形改变。损伤降低了受影响节段的IDP，平均降至骨折前值的47%（p <.001），并将压缩载荷从髓核转移至纤维环，同时也从椎间盘转移至神经弓。在相邻（未骨折）节段也观察到类似但程度较轻的影响，其中平均IDP降至基线值的73%（p <.001）。椎体成形术部分逆转了这些变化，在骨折节段和相邻节段分别将平均IDP提高至基线值的76%和81%。损伤还增加了加载下椎体的蠕变变形，尤其是在前部区域，在骨折节段观察到增加了14倍，在相邻节段增加了3倍。椎体成形术也逆转了这些变化，在骨折节段使椎体前部变形（与骨折后值相比）减少了62%，在相邻节段减少了52%。
椎体骨折对压缩载荷分担产生不利影响，并增加骨折节段和相邻节段的椎体变形。椎体成形术可部分逆转所有这些影响。
