Luo Jin, Skrzypiec Daniel M, Pollintine Phillip, Adams Michael A, Annesley-Williams Deborah J, Dolan Patricia
Department of Anatomy, University of Bristol, Southwell Street, Bristol BS2 8EJ, UK.
Bone. 2007 Apr;40(4):1110-9. doi: 10.1016/j.bone.2006.11.021. Epub 2007 Jan 16.
Osteoporotic vertebral fractures can be treated by injecting bone cement into the damaged vertebral body. "Vertebroplasty" is becoming popular but the procedure has yet to be optimised. This study compared the ability of two different types of cement to restore the spine's mechanical properties following fracture, and it examined how the mechanical efficacy of vertebroplasty depends on bone mineral density (BMD), fracture severity, and disc degeneration.
A pair of thoracolumbar "motion-segments" (two adjacent vertebrae with intervening soft tissue) was obtained from each of 15 cadavers, aged 51-91 years. Specimens were loaded to induce vertebral fracture; then one of each pair underwent vertebroplasty with polymethylmethacrylate (PMMA) cement, the other with another composite material (Cortoss). Specimens were creep loaded for 2 h to allow consolidation. At each stage of the experiment, motion segment stiffness in bending and compression was measured, and the distribution of compressive loading on the vertebrae was investigated by pulling a miniature pressure transducer through the intervertebral disc. Pressure measurements, repeated in flexed and extended postures, indicated the intradiscal pressure (IDP) and neural arch compressive load-bearing (F(N)). BMD was measured using DXA. Fracture severity was quantified from height loss.
Vertebral fracture reduced motion segment stiffness in bending and compression, by 31% and 43% respectively (p<0.001). IDP fell by 43-62%, depending on posture (p<0.001), whereas F(N) increased from 14% to 37% of the applied load in flexion, and from 39% to 61% in extension (p<0.001). Vertebroplasty partially reversed all these effects, and the restoration of load-sharing was usually sustained after creep-consolidation. No differences were observed between PMMA and Cortoss. Pooled results from 30 specimens showed that low BMD was associated with increased fracture severity (in terms of height loss) and with greater changes in stiffness and load-sharing following fracture. Specimens with low BMD and more severe fractures also showed the greatest mechanical changes following vertebroplasty.
Low vertebral BMD leads to greater changes in stiffness and spinal load-sharing following fracture. Restoration of mechanical function following vertebroplasty is little influenced by cement type but may be greater in people with low BMD who suffer more severe fractures.
骨质疏松性椎体骨折可通过向受损椎体注射骨水泥进行治疗。“椎体成形术”正逐渐流行，但该手术仍有待优化。本研究比较了两种不同类型骨水泥在骨折后恢复脊柱力学性能的能力，并研究了椎体成形术的力学效果如何取决于骨密度（BMD）、骨折严重程度和椎间盘退变情况。
从15具年龄在51 - 91岁的尸体中获取一对胸腰椎“运动节段”（两个相邻椎体及中间的软组织）。对标本施加负荷以诱导椎体骨折；然后每对标本中的一个用聚甲基丙烯酸甲酯（PMMA）骨水泥进行椎体成形术，另一个用另一种复合材料（Cortoss）进行椎体成形术。对标本进行2小时的蠕变加载以使其固结。在实验的每个阶段，测量运动节段在弯曲和压缩时的刚度，并通过将微型压力传感器拉过椎间盘来研究椎体上压缩负荷的分布情况。在屈曲和伸展姿势下重复进行压力测量，以显示椎间盘内压力（IDP）和神经弓压缩负荷（F(N)）。使用双能X线吸收法（DXA）测量骨密度。根据高度丢失情况量化骨折严重程度。
椎体骨折使运动节段在弯曲和压缩时的刚度分别降低了31%和43%（p<0.001）。IDP根据姿势下降了43% - 62%（p<0.001），而F(N)在屈曲时从施加负荷的14%增加到37%，在伸展时从39%增加到61%（p<0.001）。椎体成形术部分逆转了所有这些影响，并且在蠕变固结后，负荷分担的恢复通常得以维持。PMMA和Cortoss之间未观察到差异。30个标本的汇总结果表明，低骨密度与骨折严重程度增加（就高度丢失而言）以及骨折后刚度和负荷分担的更大变化相关。骨密度低且骨折更严重的标本在椎体成形术后也显示出最大的力学变化。
椎体骨密度低会导致骨折后刚度和脊柱负荷分担的更大变化。椎体成形术后力学功能的恢复受骨水泥类型影响较小，但在骨密度低且骨折更严重的人群中可能更大。
