Mechanical gluteal soft tissue material parameter validation under complex tissue loading

Finite element (FE) simulations of mechanical tissue loading help provide insight into internal tissue stress and strain distribution. Thus, better understanding of pressure sore aetiology and pressure sore prophylaxis can be acquired. Indispensable in the simulation process is adequate mechanical description of interacting soft tissue and body support materials. Sufficient verification of employed material parameters is required.

Gluteal soft tissue material parameters, previously derived from experimental tissue indentation of a geometrically limited buttock sub-domain are shown to be suitable in simulating complex deformation of the entire buttocks. In the context of parameter verification, defined tissue loading via a soft foam material specimen was performed. Making use of magnetic resonance imaging (MRI), the scenario was scanned to gain tissue displacement information. Anatomical surface data was reconstructed and an FE-model of the experimental situation was generated and simulated. MR-image information was compared with simulation results.

Deformation of gluteal skin/fat and passive muscle tissue and support material under loading was in good agreement with the corresponding MR-image data. Visual accordance was found for deformed skin boundary as well as for internal fat-muscle tissue boundaries by superimposing experimental and numerical output. In addition, section surface boundaries of the MR-images and the FE-model of skin/fat and muscle at the deformed state were discretized and sufficient sample points were provided. A correlation factor of R2= 0.998 for skin/fat deformation was derived, comparing simulation with MRI output.

Reliability of employed tissue material parameters for use in realistic loading scenarios at finite strains including complex tissue and bone anatomy, non-linear tissue support material, multiple tissue types and contact interactions is shown.