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Inter- and intra-batch variability in the handling characteristics and viscosity of commonly used antibiotic-loaded bone cements.

BACKGROUND
Several factors can affect the viscosity of a cement and therefore its handling characteristics. We performed an in vitro study to ascertain whether anecdotal observations of differences in handling between batches of the same brand of cement actually existed.


METHODS
3 batches of Simplex P Tobramycin (SPT), Refobacin Bone Cement (RBC), SmartSet GHV (SSG) and Palacos R+G (PRG) were tested. 6 replicates of each batch were vacuum-mixed and their viscosity in relation to time was measured under laboratory conditions using a rheometer. We examined the handling characteristics of 6 replicates of each batch after they were hand-mixed under theater conditions.


RESULTS
Inter- and intra-batch variability was seen in the viscosity of all brands of cement tested. Interbatch calculations were influenced by high intra-batch variability in viscosity. The viscosity of RBC cement was similar to that of SSG, but different to that of PRG (p = 0.01 at 5 N and p = 0.009 at 40 N).


INTERPRETATION
Our results suggest that in clinical practice, extrinsic factors such as preparation conditions and methods probably play a more important role than the intrinsic variability of cements. However, variability in handling and viscosity will exist in all brands of cement prepared under theater conditions and the surgeon must be aware of why they may act differently.