Comparison on stability of expansive pedicle screw and polymethylmethacrylate-augmented pedicle screw in osteoporotic synthetic bone

Abstract:

Objective：To compare the stability of expansive pedicle screw（EPS） and polymethylmethacrylate-augmented pedicle screw （PMMA-PS） in osteoporotic synthetic bone blocks. Methods：Thirty osteoporotic synthetic bone blocks were randomly divided into three groups（10 in each group）. A pilot hole was prepared in advance using the same method in all samples. Then，the conventional pedicle screw（CPS） was inserted into the hole in CPS group，the pilot hole was filled with PMMA（2.5 ml） followed by CPS insertion in PMMA-PS group，and EPS was inserted into blocks in EPS group. Twenty-four hours later，X-ray and CT examination and axial pullout tests were performed on all samples. The maximam pullout strength（Fmax） and energy absorbed value（EAV） were measured. Then，the destruction of blocks was observed and the diameter of hole（DOH） was measured. Results：In CPS group，the screw was surrounded directly by synthetic bone without any other materials. In PMMA-PS group，the screw was wrapped up by PMMA totally. The PMMA was evenly distributed in synthetic bone around screw，which obviously improved the local density around track. In EPS group，anterior part of EPS presented an obvious expansion in synthetic bone and formed an unguiform structure which pressed surrounding synthetic bone. Results in the ax－ial pull-out tests revealed that screw stability in both EPS group and PMMA-PS group were significantly enhanced compared with that in CPS group（P<0.05）. But screw stability in PMMA-PS group was significant higher than that in EPS group（P<0.05）. After pullout of screw，the destructions of blocks were the most severe in PMMA-PS group and the lightest in CPS group. The DOH in PMMA-PS group and EPS group were significant bigger than that in CPS group（P<0.05）. But the DOH in PMMA-PS group was significant bigger than that in EPS group（P<0.05）. Conclusion：EPS and PMMA-PS can both significantly increase screw fixation strength in osteoporotic synthetic bone blocks. In addition，EPS can avoid the shortcomings caused by PMMA. Though，EPS shows less effect on augmentation of screw stability compared with PMMA-PS in osteoporotic synthetic bone blocks，it also provides a new study direction to prevent screw loosening in osteoporosis in clinic and avoid risks caused by PMMA in traditional method.