Stress distribution in a physical buttock model: effect of simulated bone geometry.

Mechanical stresses developed in the tissue during sitting or reclining could cause bedsores in paralyzed individuals. Cushions are usually prescribed to redistribute the stresses. Two two-dimensional physical models of the buttock were developed and used to study whether the stress distribution is different with round- and flat-base bone core geometries and to find out whether the relative cushion responses are dependent on loading direction and bone core geometries. In these models, PVC gel simulated the soft tissue and a wooden core simulated the bony prominence. One model had a round-base core and the other had a flat-base bone core. A grid etched on the model allowed strain measurements, and stress calculations. The sharp-base bone core model generated large regions of high shear stress during vertical and inclined loading. However, the round-base core produced maximum compressive stress during vertical loading. The relative cushion responses were dependent on bone core geometry and loading direction.