Modification of PMMA vertebroplasty cement for reduced stiffness by addition of normal saline: a material properties evaluation.

PURPOSE: Vertebral augmentation is an established treatment for patients with pathological vertebral compression fractures. These procedures typically employ a PMMA-based bone cement, which possesses a high compressive stiffness. Because of the increased risk of subsequent fractures after vertebral augmentations, there is a desire for reducing this stiffness. The goal of our study was to examine the influence of adding isotonic saline on the biomechanical properties of PMMA vertebroplasty cement.
METHODS: A PMMA-based vertebroplasty cement was prepared according to the manufacturer's recommendations after which isotonic saline was mixed into the cement at 10, 20, and 30% (volume:volume). Testing bodies were cast, and compression and bending tests were performed. Fracture surfaces were studied using SEM. Measurements of injectability, setting temperature, and radioopacity were also performed.
RESULTS: The addition of saline solution (of up to vol-30%) led to a pronounced reduction in the compression modulus of the cement from 3409 ± 312 to 1131 ± 127 MPa. In parallel, maximal compression strength was reduced from 86 ± 4 to 33 ± 3 MPa and bending strength from 40 ± 4 to 24 ± 3 MPa. The differences regarding injectability, setting temperature, and radioopacity were small and probably of no clinical relevance.
CONCLUSIONS: The compressive stiffness of PMMA-based vertebroplasty cement can be reduced to almost a third by the addition of saline. The probable explanation is an increase in microporosity. Future simulator experiments will show whether the achieved reduction in stiffness is large enough to reduce the rate of subsequent vertebral fractures.