gms | German Medical Science

Objectives: Vertebroplasty has been used both in the treatment of painful vertebral compression fractures (VCF) as well as a prophylactic procedure to reinforce the intact but weak vertebral bodies, showing significant and rapid pain relief in these patients. However, whether augmenting the fractured vertebrae increases the risk of adjacent-level fractures remains unclear. The purpose of this study was to evaluate the influence of endplate-to-endplate cement injection in failure load and stiffness after prophylactic vertebroplasty.

Methods: Ten specimens consisting each of a central vertebral body with its attached intervertebral discs and upper and lower adjacent vertebrae were harvested from eight human cadavers and screened for bone mineral density. Each specimen was placed in a custom-made fixation apparatus (E10000, Instron, MA) and subjected to cyclic sinusoidal dynamic compression (500-1000N, 1Hz, 1800 cycles) before and after vertebroplasty. The material used for augmentation was commercial bone cement (Biomet, IN) which injection was controlled by fluoroscopy in order to achieve endplate-to-endplate filling. The augmented specimens were further cyclically loaded at steps of increasing load for a total of 4800 cycles and afterwards compressed along their central axis at a constant displacement rate of 0.5 mm/s until failure occurred. All specimens were CT scanned after augmentation and after the fracture test. Pressure was measured in the upper and lower endplates of the adjacent vertebrae using a pressure mapping sensor (4000, Tekscan, MA). Segmentation and calculation of the cement and vertebral volumes was performed in 3D Slicer - version 4.11.0. Cement volume fraction (CVF) was defined as the ratio of cement and vertebral volumes. Linear regression analysis was used to determine the correlation of the mechanical results with augmentation features. The degree of association was measured by Pearson's correlation coefficient (r).

Results and Conclusion: The average volume of cement injected to the central vertebral bodies was 10.8 ± 2.2 cm3 and mean CVF was 27.4 ± 5.2 %. Mean failure load was 5472.2 ± 1546.7 N and the mean stiffness of the specimens was 3083.3 ± 885.4 N/mm. The results show that CVF correlates positively with both failure load (r=0.177) and stiffness (r=0.421). Failure load is positively correlated with stiffness (r=0.339). No relation was found between the augmented regions and the fracture location in both central and adjacent vertebrae. The results of this study are in accordance with previous studies that demonstrated that an endplate-to-endplate filling pattern can have a strong effect on the strength and stiffness of augmented vertebrae. Previous studies show, however, that there was a trend towards lower failure loads with increased filling with cement, pointing to a possible risk of fractures in the adjacent, non-augmented vertebrae. These findings are contrary to the ones obtained in the current study.