Biomechanical Comparison of Polymethylmethacrylate Augmentation Methods in Failed Pedicle Screw Revision

AIM: To compare biomechanical results between different polymethylmethacrylate (PMMA) augmentation methods on failed lumbar pedicle screw models of animal vertebrae. MATERIAL and METHODS: Thirty lumbar vertebrae were harvested from six calves, and their bone mineral density was measured. 60 Polyaxial pedicle screws were inserted to all vertebrae. Pull-out tests were performed to all specimens on an Instron machine. The specimens were randomly divided into four groups. The same screws used in primary screwing process were labeled and used in revision. Screws in the first group were augmented by injecting PMMA into the failed screw hole with a syringe; screws in the second group by inserting bone graft and roll-shaped PMMA, screws in the third group by inserting bone graft and injecting PMMA with a syringe; and the fourth group by inserting bone graft and injecting PMMA through a fenestrated pedicle screw. The pull-out strength (POS) results of all specimens were recorded and compared with statistical analyses. RESULTS: The mean BMD of the vertebrae was 1.31 +/- 0.225 g/cm2 and no significant difference was found between the groups (p>0.05). The mean POS of the primary screws in the first, second, third, and fourth groups were 2166,5 N/m2, 2183,5 N/m2, 2508,5 N/m2, and 2005c N/m2 respectively. After the augmentation, the mean POS in the first, second, third and fourth groups were 3839 N/m2, 2874 N/m2, 2929 N/m2 and 3826 N/m2 respectively. No statistical difference was found between the groups in post-revision POS values (p>0.05). CONCLUSION: There was no significant statistical difference found in POS between the augmentation methods.