  Vertebroplasty is a minimally invasive surgical procedure used to treat
vertebral fractures, which conventionally involves injecting
polymethylmethacrylate (PMMA) bone cement into the fractured vertebra. A common
risk associated with vertebroplasty is cement leaking out of the vertebra
during the injection, which may occur due to a lack of understanding of the
bone cement's complex flow behavior. Therefore, experiments to quantify the
cement's flow properties are necessary for understanding and proper handling of
the bone cement. In this study, we aimed to characterize the behavior of the
PMMA bone cement in its curing stages to obtain parameters that govern the flow
behavior during the injection. We used rotational and oscillatory rheometry for
our measurements, as well as a custom-made injector setup that replicated a
typical vertebroplasty setting. Our results showed that the complex
viscoelastic behavior of the bone cement is significantly affected by
deformations and temperature. We found that the results from rotational tests,
often used for characterizing the bone cement, are susceptible to measurement
artifacts caused by wall slip and "ridge"-like formations in the test sample.
We also found the Cox-Merz rule to be conditionally valid, which affects the
use of oscillatory tests to obtain shear-thinning characteristics for the bone
cement. Our findings identify important differences in the measured flow
behavior of PMMA bone cement when assessed by different rheological methods,
understanding which is crucial for its risk-free usage in downstream medical
applications.
