Injection biomechanics of in vitro simulated vertebroplasty - correlation of injection force and cement viscosity.

Cement leakage is considered to be one of the major and most severe complications during percutaneous vertebroplasty. The viscosity of the material plays a key role in this context. At high cement viscosity, the risk of leakage is reduced; however, injection forces are highly increased, rendering injection difficult or even impossible. This study investigated the correlation of injection forces of poly-(methylmethacrylate) (PMMA) cement through different injection systems to the viscosity of the setting material. The in vitro simulation proved to give consistent data compared to clinically observed values. The difference of measurements carried out at room or body temperature was significant. There was an increase in injection force to be overcome after breaks during the injection process. This is caused by the accelerated setting process in that part of the injection needle that was placed in body temperature conditions. Finally, viscosity application limits of the different injection systems were estimated using a required manual force limit of 100 N. In a clinical routine, the use of a viscometer might enhance the safety of the percutaneous vertebroplasty by reducing cement extravasation and avoiding early setting of the material in the injection devices.