In vitro simulation of intraoperative vertebroplasty applied for pedicle screw augmentation. A biomechanical evaluation

Background and purpose

The purpose of this study was to evaluate the effect of an in vitro simulation of intraoperative vertebroplasty on embedded pedicle screws resistance to pullout. This method involved an application of acrylic cement into the vertebral bodies only after pedicle screws implementation.

Materials and methods

For the purpose of conducting this research, the authors used the spines of fully-grown pigs. The procedure was as follows: firstly, the pedicle screws were bilaterally implemented in 10 vertebrae; secondly, cancellous bone was removed from vertebral bodies selected for screws augmentation and lastly it was replaced by polymethylmethacrylate (PMMA). Six vertebrae with implemented pedicle screws served as a control group. The pullout strength of thirty-two screws (20 augmented and 12 control) was tested. All screws were pulled out at a crosshead speed of 5 mm/min.

Results

The PMMA-augmented screws showed a 1.3 times higher average pullout force than the control group: respectively 1539.68 N and 1156.59 N. In essence, no significant discrepancy was determined between average pullout forces of screws which were pulled as first when compared with consecutive contralateral ones.

Conclusions

An in vitro simulation of intraoperative injection of PMMA in the vertebral body instrumented with screws (intraoperative vertebroplasty) resulted in enhancing its pullout strength by 33%. Pulling of one of the pedicular screws from the augmented vertebral body did not affect the pullout resistance of the contralateral one.