Experimental and computational approach investigating burst fracture augmentation using PMMA and calcium phosphate cements

Abstract

The aim of the study was to use a computational and experimental approach to evaluate, compare and predict the ability of calcium phosphate (CaP) and poly (methyl methacrylate) (PMMA) augmentation cements to restore mechanical stability to traumatically fractured vertebrae, following a vertebroplasty procedure. Traumatic fractures (n = 17) were generated in a series of porcine vertebrae using a drop-weight method. The fractured vertebrae were imaged using μCT and tested under axial compression. Twelve of the fractured vertebrae were randomly selected to undergo a vertebroplasty procedure using either a PMMA (n = 6) or a CaP cement variation (n = 6). The specimens were imaged using μCT and re-tested. Finite element models of the fractured and augmented vertebrae were generated from the μCT data and used to compare the effect of fracture void fill with augmented specimen stiffness. Significant increases (p < 0.05) in failure load were found for both of the augmented specimen groups compared to the fractured group. The experimental and computational results indicated that neither the CaP cement nor PMMA cement could completely restore the vertebral mechanical behavior to the intact level. The effectiveness of the procedure appeared to be more influenced by the volume of fracture filled rather than by the mechanical properties of the cement itself.

Figure 1

Experimental and computational methodology used within this study

Figure 2

Loading Scenario and radiopaque marker location

Figure 3

Example of FE model of single vertebra specimen

Figure 4

Comparison of mean of specimen stiffness (± SD) pre- and post-augmentation using the different cement types (*significant difference p < 0.05)

Figure 5

Comparison of mean of specimen ultimate failure load (± SD) pre- and post-augmentation using the different cement types (*significant difference p < 0.05)

Figure 6

FE model stiffness predictions compared to experimental results for traumatically fractured and augmented specimens

Figure 7

Bland–Altman difference plot of specimen stiffness pre and post augmentation, difference (experimental–FE) vs. average of values obtained from experimental and FE methods