Evaluation of a synthetic vertebral body augmentation model for rapid and reliable cyclic compression life testing of materials for balloon kyphoplasty.

Screening of augmentation materials for use in balloon kyphoplasty (BKP) may be carried out using vertebral bodies (VBs) prepared from fresh cadaveric or animal model spines, but this approach has many drawbacks. Alternatively, a validated synthetic VB augmentation model may be used. In the present work, such a model-a cube (26 mm sides) of low-density polyurethane foam with a centrally located through-thickness cylindrical hole (diameter = 4 mm) completely filled with a bolus of augmentation material-was used to compare two BKP augmentation materials with very different chemistries (a high-viscosity acrylic bone cement (PMMA) and a calcium phosphate bone substitute (CP)) in cyclic compression life tests. The test conditions were considered physiologically relevant: the model was immersed in phosphate buffered saline solution, at 37 degrees C; the frequency was 3 Hz; and the maximum load was either 1150 N or 2300 N (corresponding to a maximum stress of 1.7 or 3.4 MPa). At the high load, all four PMMA and two out of seven CP specimens ran out to 1 million cycles. CP specimens consistently ran out at the low load. The use of this model for rapid and reliable ex vivo screening of BKP augmentation materials was considered both valid (because of the clear demarcation seen in the qualitative and quantitative results obtained with the two materials tested) and appropriate (that is, clinically relevant to BKP).