A Biomechanical Study on the Pull-Out Strength of Pedicle Screw Augmented with Polymethylmethacrylate(PMMA)- Cadaveric Study -

ABSTRACT

OBJECTIVE: The authors evaluate the differences in the pedicle screw pull-out strength between an unaugmented screw and a screw augmented by high pressurized PMMA in an embalmed human lumbar cadaveric spine. METHODS: Pedicle screws were inserted in the 50 pedicles of cadaver lumbar spine after measuring the bone mineral density(BMD) of the specimens. The pedicle screw was inserted without augmentation on the left pedicle and with augmentation by a vertebral reconstruction with high pressurized PMMA on the right side. The pedicle screw was inserted before the hardening of bone cement on the right side. A computed tomographic scan was done to evaluate the location of the PMMA and PMMA/ screw interface. After that, a screw pullout strength test was performed. RESULTS: There were positive correlations between the pull-out strength and BMD in the control group (r=0.7339). The average pull-out strength of the augmented group was 168% greater than that of the control group(p<0.05). The pull-out strength of the augmented group was correlated with in the volume of the PMMA. CONCLUSION: A pedicle screw that is augmented with PMMA will provide a more rigid fixation than that of an unaugmented screw, especially in the low BMD group of the specimens.