Vertebral compression model and comparison of augmentation agents

STUDY DESIGN Biomechanical study. OBJECTIVES To evaluate the compression strengths of various bone fillers used in treating vertebral compression fractures using a third-generation sawbone model and to evaluate the viability of this novel model as an alternative to actual human or animal vertebrae for biomechanical testing of vertebral-filling materials. METHODS Cavities were created in the osteoporotic vertebral body sawbone models and filled with PMMA, SRS, MIIGX3 HiVisc, and BoneSource fillers. These were cured according to manufacturers' recommendations and then tested to failure in the compression model. Elastic modulus was calculated and compared with the control group which was not augmented. RESULTS The mean modulus of elasticity for the control group vertebrae was 92.44 ± 19.28 MPa. The mean modulus of elasticity was highest in the polymethylmethacrylate (PMMA) group (195.47 ± 2.33 MPa) and lowest in the MIIG group (25.79 ± 4.77 MPa). The results for the SRS-tricalcium phosphate group (79.14 ± 20.20 MPa) were closest to the control group, followed by the BoneSource group (57.49 ± 8.35 MPa). Statistical analysis, for comparison of individual group means, identified significant differences between the control group and all other groups (P < .05), with the exception of the SRS-tricalcium phosphate group (P = .65, versus control). The modulus of elasticity for the PMMA group was significantly higher than all other groups (P < .001). CONCLUSION The third-generation osteoporotic sawbones model simulates in vitro physiological specimen function. It was effective for comparing which osteoconductive agents may provide adequate strength while minimizing potential adjacent level fracture. Increased stiffness was seen with PMMA compared with the unaugmented control as well as with calcium phosphate or calcium sulfate cements suggesting that these may reduce adjacent segment fractures.