The mechanical behaviour of skin and soft tissues is critically important in the formation of pressure ulcers, which we know can be caused in a very short time by particular types of mechanical loading. Understanding exactly how this happens is critical if we are to predict and avoid injury, but it requires us to journey to the frontiers of engineering mechanics, where we are still struggling to understand how soft tissues behave.
The mechanical behaviour of skin and soft tissues is very unusual, highly adapted to its function and difficult to understand from an engineering perspective. We do not currently have good mathematical models to describe their behaviour, and measuring how they behave and extracting their properties from the results are problematic. Modelling soft tissues and interpreting the results is therefore challenging.
We have modelled the stresses in the heel during loading against a hard surface using different material models for the soft tissues. Depending on the model used, the results can be very different, and different criteria for possible injury can also produce very different results. For example, different measures of stress can predict either superficial injury to the skin or deep injury to the tissues around the bone.
It is important to understand these challenges in soft tissue modelling, and more work is needed to address them, by improving our models, our understanding of injury thresholds, and the validation of models through experimental measurements, for example using MRI or other imaging techniques.