Novel methodology for assessing cement injection behaviour in cancellous bone

Understanding the cement injection behaviour in cancellous bone and accurately predicting the cement placement within the vertebral body is extremely challenging. We propose a novel method using reproducible and pathologically representative 2D and 3D bone surrogates to help study the influence of cement properties on injection behaviour. Bespoke methodology was developed to control the injection volume and flow rate, measure the injection pressure, and allow visualization and quantitative analysis of the spreading distribution. Morphology analysis showed that the variability in the 2D and 3D bone surrogates was very low, indicating that the geometrical structure of the surrogates was constant. The overall pore size of the surrogates was very similar to that reported for human osteoporotic vertebral cancellous bone, indicating that the surrogates were pathologically representative. Injections performed into the 3D surrogates revealed that an increase in the fluid starting viscosity significantly increases the injection pressure in all surrogates, decreases the risk of leakage for osteoporosis surrogates only, decreases the mean spreading distance for multiple myeloma surrogates only and increases the sphericity causing a more uniform spreading pattern for the metastasis surrogates only. Injections performed into the 2D surrogates highlighted the influence of cement formulations and model structure on the injection behaviour and showed that (i) cements with similar composition/particle size have similar flow behaviour, (ii) cements with a high liquid-to-powder ratio cause irregular filling patterns and have a high risk of leakage, and (iii) the injection behaviour of certain cement formulations improves in the presence of lesion or fracture, suggesting the notion of pathology specific bone cements. The developed methodology provides a fast, robust tool for discerning subtle differences in bone cement formulations and allows comprehensive assessment of cement flow behaviour through controlling the surrogate morphology, controlling the injection parameters, measuring the injection pressure, and allowing the visualization and quantitative analysis of the spreading distribution. The advantage of this methodology is that it provides a clinically relevant representation of cement flow patterns and a tool for validating computational simulations.