Biomechanical study of poly DL-lactic acid biodegradable fusion cage of the lumbar vertebrae / 中华骨科杂志

ABSTRACT

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.