Purpose of the study: To compare the anchorage strength of Socon CS cannulated pedicle screws (B. Braun, Aesculap) with that of Socon screws in human cadaver vertebrae, using pull-out strength testing.
Material: Twelve samples involving T12 to L3 vertebrae were prepared and a total of 20 pedicle screws, 10 Socon CS and 10 Socon screws, were inserted in them. All screws were 55 mm in length and 6 mm in diameter. After placement, Socon CS pedicle screws were augmented with bone cement (Cimplant cement application kit, B. Braun, Aesculap).
Methods: Both Socon CS and Socon screws were subjected to monotonous loading in the testing device ZWICK Z 020-TND with tensile stress applied in the screw axis. We evaluated the magnitude of strength resulting in screw loosening and the relationship between this strength and bone density of the sample.
Results: Bone density of measured samples corresponded either to osteopenia, i.e. T-score range of -1 to -2.5 SD (standard deviation) or osteoporosis, i.e. T-score -2.5 SD. The average bone density of all samples corresponded to a T-score of -3.1 SD. Bone-screw linkage was found to be associated with both bone-cement and screw-cement interface. Pull-out strength was significantly higher for the Socon CS than the Socon screws (t-test, p<0.0005). In the Socon screws, the linear correlation between pull-out strength and bone density was significant at a 5% level of statistical significance (p=0.008) while, in the Socon CS screws, it was not significant (p=0.065).
Discussion: The poor quality of osteoporotic bone is responsible for a higher frequency of implant failure due to loosening, particularly when implants developed for healthy bone are used. In this biomechanical study, we tested one of the possibilities of how to reduce the risk of implant failure by pedicle screw augmentation with bone cement.
Conclusions: The results of this study confirm the hypothesis that the anchorage of Socon CS cannulated pedicle screws with bone cement augmentation is disrupted by significantly higher pull-out strength than that of Socon screws, when subjected to monotonous loading. However, more clinical studies are needed to evaluate clinical outcomes.