The radiological and biomechanical assessment using cement augmented cannulated pedicle screw (Biomet®, Omega 21®) and the correlation of the cement volume to the pullout strength needed for each screw Cadaveric vertebrae of different lumbar levels were used. Through cannulated pedicle screw a definite volume of cement was applicated. The bone volume occupied by cement was assessed by means of segmentation after Computer Tomography. Biomechanical Pullout tests and statistical correlation analysis were then performed The maximum pullout strength was 1361 N and the minimum pullout strength was 172 N (SD 331 N). The maximum cement volume was 5,29 cm3 and the minimum 1,02 cm3 (SD 1,159). The maximum cement diameter was 26,6 cm and the minimum cement diameter was 20,7 cm (SD 1,744). There is statistically significant correlation between the pullout strength and the injected cement volume (p<
0,05). The cannulated pedicle screw was used for a better fixation in the vertebral body. The cement augmentation with this technique is easier and seems to be safer than cement augmentation of non cannulated screws. Pullout strength of the cannulated screws correlates positively with the cement volume. It is though not influenced either by the total vertebral volume or by the ratio cement volume to vertebral volume or by the maximum diameter of the cement drough
The influence of the intravertebral length of vertebral screws on their pull out strength. 64 Cadaveric vertebrae of different lumbar levels were used. By means of Computer Tomography the length of the screw in the bone was assessed. The ratio screw length in bone to the longest possible screw in bone was built. Biomechanical Pullout tests and statistical correlation analysis were then performed The maximum pullout strength was 1602 N and the minimum pullout strength was 96,4 N (SD 356,9 N). The maximum ratio of the inserted screw was 95,9% and the minimum was 58,8% (SD 0,7%). There is no statistically significant correlation between the ratio of the inserted screw and the pullout strength needed. Moreover, there is a statistically significant correlation between bone mass density and pullout strength (p<
0,05). The fixation of pedicle screws is better in a non osteoporotic vertebral body. Pullout strength and bone mass density correlate significantly whereas there is no correlation between the insertion length of the screw and the pullout strength under the condition that the insertion ratio is greater than 58,8 %. Factors such as insertion angle of the screw need to be evaluated, and new techniques for pedicle screw fixation in osteoporotic vertebrae need to be developed
