A biomechanical model for real-time simulation of PMMA injection with haptics.

We have developed a computationally efficient rheological model to simulate polymethylmethacrylate (PMMA) injection into cancellous bone during percutaneous vertebroplasty. The model employs the Hagen-Poiseuille law to predict pressure drop across a delivery cannula with viscoelastic changes of curing PMMA modeled via a time and shear-rate-dependent power law. The power law was derived based on dynamic rheological testing of curing PMMA samples. In conjunction with a branching-pipe geometrical model that is reconstructed from micro-computed tomography scans of cancellous bone for estimating pressure changes during PMMA flow in bone, the method provides a fast estimation of overall injection pressure, and, hence, the reaction force during manual PMMA injection.