FLUID STRUCTURE INTERACTION MODELLING OF LOADING WITHIN CANCELLOUS BONE

Osteoarthritis (OA) is the most prevalent musculoskeletal disease globally, giving rise to a significant healthcare burden and reducing sufferers' quality of life. The mechanism by which pain is generated in OA is not fully understood, it is considered that small amounts of damage to the articular surfaces do not give rise to clinically important levels of pain. Pain is thought to be generated when the disease processes alter loading in the bone. To gain insight into the possible mechanisms by which pain is generated, detailed modelling of the cancellous bone was performed, together with experimental studies. Cancellous bone has a considerable amount of fluid present in the marrow. To take account of this fluid during loading an approach other than straight forward finite element (FE) analysis is needed. Fluid structure interaction (FSI) models couple the effects of fluid and solid phases. Previous studies have used idealised geometries, this work was based on geometry obtained directly from bone. The geometry for the mesh of the FSI model was obtained by μ-CT scanning and segmenting a porcine tibia specimen. This geometry was then used to created an experimental specimen by segmenting and enlarging the μ-CT data and 3D printing a representative cube of trabecular bone. The experimental model was used to measure pressure changes resulting from vertical displacement applied to the top surface of the cube, using pressure sensors. Two fluids were used, water and silicon oil ( n = 20/fluid). The computational model used the modified OpenFOAM fsiFoam solver. A two-phase fluid solver was chosen to mimic the free surface of the fluid during testing. The solid domain was subjected to a vertical displacement as per the experiments. Pressure data were extracted at the location of the equivalent experimental pressure sensors. After validating the model against the experimental data, the model was run using physiological data input for trabecular bone and a power-law rheology model for bone marrow. The experimental loading of the bone structure resulted in a variation of pressure throughout the structure ranging from 0.01 kPa - 0.025 kPa. The fluid type further influenced this effect. The simulation results for the pressure were compared and demonstrated similar variations. The physiological model showed variation in pressure depending on the structural environment as well. The current work highlights the importance of taking into account the complex structure of trabecular bone when modelling loading of bone.