Objective To investigate biomechanical analysis of poly DL-lactic acid (PDLLA)biodegradable fusion cage of the lumbar vertebrae in vivo degradation. Methods Forty-eight healthy adult porcine were divided into experimental group and control group at randomly. PDLLA cage full of autogenous bone and bone block with the same size were planted in L45 intervertebrae respectively. At the 1st, 3rd, 6th,9th, 12th, and 18th month postoperatively, the animals were sacrificed and the surgical spinal segment was observed. The range of motion (ROM) was measured. Results The ROMs had no statistical differences at all motion directions between the two froups at the 1st month postoperatively. But the ROMs of experimental group were greater than those of control group at extension direction at the 3rd and 6th month postoperatively. The ROMs of extension was the greatest while the ROMs of right rotation was the least in both groups. At the 9th month postoperatively: the ROMs of experimental group greater than those of control group except at rotation. The ROMs of right rotation was the least in both groups. The greatest ROMs was at extension in experimental group and at right bending in control group. ALL ROMs tended to decrease and the ROMs of extension had comparability between tow groups. At the 12th month postoperatively, experimental group had greater ROMs at extension and left bending and less ROMs at other directions. Likewise statistical differences showed only at extension. 18th month postoperatively all ROMs were close between two groups. Conclusion After PDLLA cage is planted, the first 3 months is autologous stable stage. The period of 3rd to 6th months is easily released stage. The operative segments are stable from 9th to 12th months and acquired.Critical period between stability and instability is from 6th to 9th months. Bone fusion is from 12th to 18th months postoperatively.%目的 探讨聚-DL-乳酸(poly DL-lactic acid,PDLLA)可降解腰椎椎间融合器在体内降解过程的生物力学变化规律,为进一步临床研究提供理论基础.方法 48头健康成年家猪随机分为实验组和对照组,分别在L4.5椎间隙植入填充自体骨的PDLLA可吸收腰椎椎间融合器或大小相当的自体骨块.分别在术后1、3、6、9、12及18个月处死动物取材.在脊柱三维运动试验机上模拟腰椎的三维运动进行屈伸、左右侧屈和左右轴向旋转运动,进行非破坏性生物力学测试来观察融合节段的稳定性.结果 1个月时两组在各个状态的运动范围差异均无统计学意义,术后3个月实验组的运动范围均大于对照组,但其差异除后伸状态外均无统计学意义.在术后6个月时实验组的测量结果 均大于对照组,此时二者在右旋最小,后伸最大,两组测量值只有在后伸状态差异有统计学意义.在术后9个月时测量结果 除左右旋转运动外实验组均高于对照组,此时仍是右旋最小,实验组后伸状态最大,对照组在右侧屈最大,但各状态数值相比差别趋于减小,此阶段只有后伸状态差异有统计学意义.术后12个月时只有后伸和左屈时实验组大于对照组,其余均小于对照组,两组相比后伸状态有统计学意义.术后18个月时两组各状态的运动范围相近.结论 PDLLA可降解腰椎椎间融合器植入体内前3个月为自身稳定期,3～6个月为易松动期,6～9个月处于稳定与非稳定之间的临界期,9～12个月进入稳定期,植入体内12～18个月达到骨融合期.
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