The intravertebral pressure and cement distribution in cadaveric vertebroplasty with and without unilateral pulsed jet lavage were recorded and compared. The unilateral lavage method in this study was an original design applied to vertebroplasty. Many reports have shown that lavage technique can remove fat and bone marrow and reduce intravertebral pressure in vertebroplasty compared with those of conventional cement injection[6,7,10]. However, these trials were bipedicular, which meant that lavage was performed on one side and suction was conducted from the contralateral side. However, in clinical practice, many surgeons, including our group, still prefer unilateral vertebroplasty because this process has been reported to present short- and long-term clinical outcomes similar to those of the bilateral technique[11-12]. The unilateral method involves shorter operation time[11,13] and less X-ray exposure frequency and trauma[14,15]. To our knowledge, our study was the first to report the application of unilateral lavage in vertebroplasty.
The results showed that unilateral lavage significantly reduced intravertebral pressure and cement leakage. Pulsed saline lavage could remove fat and marrow, as shown by the intravertebral images from the miniature video camera. After irrigation, the space became clearer, and the trabeculae could be distinguished. Yang et al.[16] also reported the effect of pulsed lavage to remove the bone marrow, and similar positive outcomes were achieved. With less fat and marrow, the space in the trabeculae was expanded and would accommodate more bone cement[17-19].Hence, less pressure would be transmitted and recorded from the contralateral side of the vertebral body. Less bone leakage could also be achieved, and this finding was reported in previous bilateral lavage studies[6,7].
The results also showed an interesting pattern of the changes in the recorded pressure during vertebroplasty. Two peaks, which corresponded to the two steps of bone cement injection, appeared in the pressure curve. Given the accumulating effect of the bone cement, the second peak did not start from the base line, and the value was higher than the first peak. This adding-on phenomenon showed that more elaborative inspection should be performed during the latter stage of bone cement injection to rule out cement leakage or other detrimental effects caused by higher intravertebral pressure.
CT scans were used to assess cement distribution. From gross inspection, the cement in the irrigated samples was more even and homogeneous than that in the unirrigated ones. Compared with the control group, the density of bone cement in the irrigation group tended to be more consistent and the borders were smoother. This may be a result of removing bone marrow and fat which were barriers in the cement diffusion process. The composition of bone cement clumps was simple and the resistance of bone cement to diffuse was reduced. So the cement diffusion tended to be regular. The leakage rate was lower in the irrigated group than in the unirrigated ones. The CMV was smaller in the former than in the latter. The CMV represented the volume, which included the filled cement, trabecula, and remaining fat and marrow. The decrease in CMV further verified the effect of removing fat and marrow from the vertebral body through irrigation.
In this study, an originally designed unilateral pulsed jet lavage system was applied and could reduce the intravertebral pressure and leakage during vertebroplasty. One limitation of our study was its in vitro nature. Without in vivo studies, the decreased intravertebral pressure could not be directly correlated with the reduced rate of fat or cement embolism during vertebroplasty. Another limitation was the small sample size, which could cause an adverse effect on data analysis. Further in vivo studies are recommended to validate the clinical values of a unilateral jet lavage system in vertebroplasty.