Kayanja Mark M, Togawa Daisuke, Lieberman Isador H
Department of Orthopaedics, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA.
Spine J. 2005 Jan-Feb;5(1):55-63. doi: 10.1016/j.spinee.2004.08.005.
Osteoporotic compression fractures are an important public health concern, leading to significant morbidity, mortality and economic burden. Cement augmentation procedures used to treat these fractures alter the biomechanics of the fractured segment, which could promote adjacent failure. However, if alignment is improved or restored, there will be less risk of adjacent failure.
To determine the effects of load (compression/flexion), adjacent vertebral location (superior/inferior) and augmentation on vertebral segment stiffness and adjacent vertebral strain in the upper and lower thoracic spine.
Human cadaveric thoracic spine segments were tested under load control before and after the creation of experimentally augmented vertebral compression fractures.
Six T1-T5 and six T8-T12 segments were obtained from eight thoracic spines with known bone mineral density (BMD). Rosette strain gauges were applied to T2, T4, T9 and T11 to measure strain adjacent to the experimental fracture sites T3 and T10. Two compression fractures were created in succession, the first in flexion preceded by a weakening defect in T3 and T10 and the second created in an adjacent vertebra in compression without prior weakening. The first fracture was reduced with the inflatable bone tamp (IBT) and augmented with cement. Compression and flexion tests were performed before and after the first fracture while measuring vertebral cortical shear strain on T2, T4, T9 and T11 and stiffness of the entire segment. Strain and stiffness were compared by using a repeated measures analysis using adjacent vertebral location (superior/inferior), augmentation and load (compression/flexion) as factors.
The mean BMD was 0.61+/-0.11 g/cm(2) (T1-T5) and 0.78+/-0.07 g/cm(2) (T8-T12). Stiffness in compression and flexion increased with load (p<.05, and p>.27, respectively). Augmentation reduced compressive and bending stiffness (p=.23, and p=.19, respectively), whereas the adjacent vertebral strain increased (p>.11). The adjacent strain in flexion was much greater than in compression (p<.03). Cement augmentation caused greater amounts of inferior than superior adjacent strain (p>.19). The applied moment at first fracture was 2.98+/-1.28 Nm (T1-T5) and 8.44+/-1.02 Nm (T8-T12). The compressive load at second fracture was 1122+/-993 N (T1-T5) and 2906+/-1008 N (T8-T12). Adjacent vertebral strain during the second compression and flexion tests exceeded that during the first compression and flexion tests (p=.11). Adjacent vertebral strain at second fracture exceeded that at first fracture (p=.007) and was greater on the superior adjacent vertebra than the inferior (p=.47).
With axial compressive loads, the addition of flexion increases fracture risk. Cement augmentation of a fractured vertebral segment reduces stiffness while increasing both the superior and inferior adjacent cortical strain. This increment in strain that is greatest on the inferior adjacent vertebra effectively redistributes loads from the superior adjacent vertebra to the inferior adjacent vertebra, sparing the superior adjacent vertebra from failure.
骨质疏松性压缩骨折是一个重要的公共卫生问题，会导致严重的发病率、死亡率和经济负担。用于治疗这些骨折的骨水泥强化手术会改变骨折节段的生物力学，这可能会促使相邻节段发生破坏。然而，如果对线得到改善或恢复，相邻节段发生破坏的风险将会降低。
确定负荷（压缩/屈曲）、相邻椎体位置（上方/下方）以及强化对胸段脊柱上下节段椎体刚度和相邻椎体应变的影响。
在人为制造实验性椎体压缩骨折前后，对人类尸体胸段脊柱节段进行负荷控制测试。
从8具已知骨密度（BMD）的胸椎获取6个T1 - T5节段和6个T8 - T12节段。将应变片贴于T2、T4、T9和T11，以测量与实验骨折部位T3和T10相邻处的应变。连续制造两个压缩骨折，第一个在屈曲状态下制造，之前先在T3和T10制造削弱缺损，第二个在相邻椎体以压缩状态制造，且之前没有进行削弱。第一个骨折用可膨胀骨填充器（IBT）复位并用骨水泥强化。在第一个骨折前后进行压缩和屈曲测试，同时测量T2、T4、T9和T11的椎体皮质剪切应变以及整个节段的刚度。使用重复测量分析比较应变和刚度，将相邻椎体位置（上方/下方）、强化和负荷（压缩/屈曲）作为因素。
平均骨密度为T1 - T5节段0.61±0.11 g/cm²，T8 - T12节段0.78±0.07 g/cm²。压缩和屈曲状态下的刚度随负荷增加（分别为p<0.05和p>0.27）。强化降低了压缩和弯曲刚度（分别为p = 0.23和p = 0.19），而相邻椎体应变增加（p>0.11）。屈曲状态下的相邻应变远大于压缩状态下的相邻应变（p<0.03）。骨水泥强化导致下方相邻应变大于上方相邻应变（p>0.19）。第一次骨折时施加的力矩为T1 - T5节段2.98±1.28 Nm，T8 - T12节段8.44±1.02 Nm。第二次骨折时的压缩负荷为T1 - T5节段1122±993 N，T8 - T12节段2906±1008 N。第二次压缩和屈曲测试期间的相邻椎体应变超过第一次压缩和屈曲测试期间的相邻椎体应变（p = 0.11）。第二次骨折时的相邻椎体应变超过第一次骨折时的相邻椎体应变（p = 0.007），且上方相邻椎体的应变大于下方相邻椎体的应变（p = 0.47）。
在轴向压缩负荷下，增加屈曲会增加骨折风险。骨折椎体节段的骨水泥强化降低了刚度，同时增加了上方和下方相邻皮质的应变。下方相邻椎体上最大的应变增加有效地将负荷从上方相邻椎体重新分配到下方相邻椎体，使上方相邻椎体免于破坏。
