Abstract
STUDY DESIGN
Expansive pedicle screws (EPS) and polymethylmethacrylate-augmented pedicle screws (PMMA-PS) were inserted into osteoporotic synthetic bones, which were then tested by radiographic and biomechanical examinations.
OBJECTIVE
To compare the stability of EPS and PMMA-PS with that of a conventional pedicle screw (CPS) in an osteoporotic synthetic bone.
SUMMARY OF BACKGROUND DATA
It is a significant challenge for orthopedic surgeons performing transpedicular fixation in the osteoporotic spine. Prior studies have suggested that both EPS and PMMA-PS can increase the screw stability effectively. However, there are no biomechanical comparisons of EPS and PMMA-PS, especially in primary spinal surgery in osteoporosis.
METHODS
Thirty osteoporotic synthetic bone blocks were divided into 3 groups randomly. A pilot hole was prepared in advance in all samples by the same method. Then, the CPS was inserted directly into the pilot hole in the CPS group; the hole in the PMMA-PS group was first filled with polymethylmethacrylate (PMMA; 2.5 mL) and then inserted with CPS, and the EPS was inserted directly into the blocks in the EPS group. Twenty-four hours later, x-ray and computed tomography examination and axial pullout tests were performed on all samples; the block destructions were then recorded, and the hole diameters were measured.
RESULTS
In the CPS group, the screw was surrounded directly by the synthetic bone without any other materials, whereas in the PMMA-PS group, the screw was totally wrapped up by PMMA, and the PMMA was evenly distributed in the synthetic bone around the screw, indicating obvious improvement of the local density around the track. In the EPS group, the anterior part of the EPS presented an obvious expansion in synthetic bone and formed an unguiform structure pressing the surrounding synthetic bone. Screw stabilities in both the PMMA-PS and the EPS groups were significantly enhanced compared with those in the CPS group, and the screw stability in the PMMA-PS group was significantly higher than that in the EPS group. After the pullout tests, the block destructions were the most severe in the PMMA-PS group and the lightest in the CPS group. Hole diameters in the PMMA-PS and the EPS groups were significantly larger than that in the CPS group, whereas the diameter of the hole in the PMMA-PS group was significantly greater than that in the EPS group.
CONCLUSIONS
EPS can significantly increase the strength of screw fixation compared with CPS in osteoporotic synthetic bone. Although EPS shows a weaker fixation strength compared with PMMA-PS in the osteoporotic synthetic bone, it may still provide an alternative option to prevent screw loosening in the clinical treatment of osteoporosis.
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