Experimental Study About The Effects Of The Bone Cement Leakage On The Intervertebral Disc In Vertebroplasty

Objective: To study whether bone cement can lead to disc degeneration, and the correlation of degeneration degree to the time after operation, the doses and the kinds of bone cement. Materials and Methods: Sixteen majority canis familiaris (15～17kg) were randomly divided into 2 time groups. 5 lumbar intervertebral discs(L1/2～L5/6) in every dog were classified into 3 groups (1 control group and 2 bone cement groups (PMMA and CPC)). Each of cement groups was classified into 2 dose subgroups (0.1ml and 0.3ml). X-ray was performed immediately after the dogs were anesthetized. Then, the dogs were stabbed by 18-gauge needle into the lumbar intervertebral discs, and cement was injected into them. Control discs were only stabbed and injected with nothing. X-ray, magnetic resonance image and histology of all discs were performed at 12 and 24 week after operation. The %Disc height index (%DHI) was calculated by comparing preoperative X-ray film with postoperative one. The T2-weighted mid-sagittal images of discs were analyzed qualitatively for evidence of degeneration. Quantitive analysis of these images was performed, MRI index (the product of nucleus pulposus area and average signal intensity) of each disc was calculated. We refered Masuda's standard of histological grading scale. By histology examination, discs were graded by assessing the annulus fibrosus, the border between the annulus fibrosus and nucleus pulposus, the cellularity of the nucleus pulposus and the matrix of the nucleus pulposus. The data were statistically analyzed by SPSS 10.0. Result: Intervertebral disc degeneration was not found in control groups. However, in bone cement groups, ruptured or serpentined patterned fibers, interrupted border between the annulus fibrosus and nucleus pulposus, decreased cellularity of the nucleus pulposus and condensed matrix of the nucleus pulposus, were found in histologic results. The degree of intervertebral disc degeneration in bone cement groups is varied with different observing time,cement dose and cement category. The %DHI,MR index and histology grade are not significantly different between two different time control groups under the t tes(tP>0.05). In 12 weeks'group, there is significantly different between the control group and the bone cement groups under analysis of Variance (P<0.05), as well as in 24 weeks'group (P<0.05). In 12 weeks'group, the %DHI of PMMA-0.3ml group is significantly different with the control (P<0.05), while the %DHI of the other three groups has no significant difference with the control (P>0.05), under Dunnet-t test. In 24 weeks'group, the %DHI of the cement groups is significantly different with the control. No matter in the 12 weeks'group or in the 24 weeks'group, the MR index and histologic grade of cement groupsare significantly different with the control group(P<0.05). There is significant difference between the different time,different doses and different category of bone cement in cement bone groups under Univariate Analysis of Variance(P<0.05). Conclusion: PMMA and CPC can lead intervertebral disc to degeneration. Intervertebral disc degeneration induced by PMMA is more serious than that of CPC. Intervertebral disc degeneration degree is correlative to the time after operation and the doses of bone cement.