C. Lavergne, C. Sender, B. Donazon. (Toulouse, France)
Vertebroplasty is now regarded as a safe and effective treatment of osteoporotic vertebral body compression fractures in terms of pain relief and disability improvement . But despite these demonstrated benefits, vertebroplasty using PMMA bone cements has to be done with caution because of the potential complications due to the material, such as the toxicologic effects related to the MMA monomer released during polymerisation. Taking into account these considerations, a necessity exists for investigations of the amount of monomer released during vertebroplasty under conditions that more closely approximate in vivo use.
Accordingly, the aim of this study was to determine the release of monomer from PMMA bone cement during polymerisation.
MATERIALS & METHODS:
The experimental procedure involved immersion of reacting monomer powder mixtures into distilled water and subsequent assay of the aqueous media for MMA monomer measurement by gas chromatography.
Commercial vertebroplasty bone cements were used for this study: Spineplex, Stryker; Osteopal V, Heraeus Medical; Opacity+, Teknimed and SpineFix, teknimed. Each cement formulation was analysed in duplicate.
Mixing was performed for 1 minute for all cements with the Mini Malax vertebroplasty kit at a constant temperature of 23_C ± 1_C.
To measure the monomer release, 4 ml of mixed bone cement were injected into aqueous media at 37_c. Aliquots of liquid samples were withdrawn at different periods of time following injection and analysed.
RESULTS & DISCUSSION:
As already observed in previous studies , the main proportion of monomer release occurred within the first minutes after injection and then remained constant.This first period corresponds to the time during which the monomer powder mixture is curing and cannot be avoided as the cement has to be inserted into the vertebra while it is still injectable before final setting occurs. The amount of released MMA ranged between 3 and 8 mg/ml of bone cement volume, the highest levels being obtained for Spineplex bone cement. These amounts are quite comparable to results reported by other authors 
The test quantity of 4ml used in this study, the mean quantity injected into a vertebra, represented volumes two to three times lower to those used for hip and knee arthroplasty. We can then reasonably think that the risks encountered by the patients during vertebroplasty are less important than for an arthroplasty, provided that manufacturer recommendations are respected.
The amount of monomer released during polymerisation was found to be comparable for all cements except Spineplex which exhibited a higher release.
By increasing the time interval before injecting the cement, a technique employed in vertebroplasty to get the optimal viscosity that permits to avoid leakages, the amount of monomer released should be reduced.
More studies taking into account the viscosity and then as a consequence the injected volume and effective surface could help to improve the safety of the vertebroplasty technique.
1) Afsal S. et al, Pain Physician (2007). 559-63.
2) Schoenfeld C. M. et al., J biomed Mater Res (1979), 135-147.
3) Boger, A. et al., J Biomed Mater Res B Appl Biomater (2008). 474-482.