Abstracts Category : Other

In vitro comparative assessment of the mechanical properties of a PMMA cement and a GPC cement for vertebroplasty

by Omar A Abouazza

Background:This study examines some of the properties of cements that could be used in vertebroplasty. Polymethylmethacrylate (PMMA) is the gold standard cement, however, some of its biomechanical properties may compromise its deployment. For example, it has a much higher Youngs modulus of elasticity that makes it much stiffer than the bone it is injected into. This can result in further fractures of these surrounding vertebrae.This study involves the testing of an alternative cement. This testing has uniquely been carried out on human cadaveric bone.Aims:The main aim of this study was to further develop an understanding of a new Glass Polyalkenoate Cement (GPC), by carrying out comparative testing with the PMMA cement. Tests were undertaken that were necessary to bring it closer to its end application in a theatre setting.Methods:Testing was performed to assess the effect of gamma irradiation used for sterilisation, on the glass transition temperature (Tg), as well as its rheology including working and setting times, thus assessing its handling and finally its mechanical properties, namely the compressive strength (CS) and the biflexural strength (BFS).In addition, the injectability of the cement was assessed on attempting to load it into syringes with bone trocars attached for vertebroplasty cement injection into the vertebral bodies. Comparison was also made between the GPC cement and the PMMA cement following cement injection into cadaveric human, lower thoracic and lumbar vertebrae looking at the bone mineral density of the injected vertebrae, the zones of cement penetration into the injected vertebrae, the ultimate load failure on compression and the various severity and locations of the vertebral height loss and vertebral compression.Results:Gamma irradiation did not affect the glass transition temperature (Tg), which is an indirect measure of the glasss structure, however, it did cause a colour change in the GPC cement from white to grey. There was no difference in the working times of the GPC cement pre and post-gamma irradiation. More importantly, it was demonstrated that the mechanical properties of the cement were altered with a decrease in both the compression strength and the biflexural strength of the GPC cement post-irradiation compared to pre-irradiation on all tested days. The cement setting medium (blood or saline) was not a statistically significant factor in this analysis (p=0.12).On testing the cements after injection into cadaveric human vertebrae, there was no statistically significant difference in the mean bone mineral density (BMD) across all the groups for either the superior (p=0.85) or inferior (p=0.24) vertebrae, or the average of the two (p=0.45), thus randomization of vertebral units for testing was effective.The GPC cement had very short working times which made loading the cement into syringes quite difficult and resulted in a 100 percent failure of injection via the trocars. Furthermore, it was found to have no penetrance into the anterior third of the vertebraeAdvisors/Committee Members: Dunne, Colum, Condon, Finbarr.