  In the last decade, the role of shearing loads has been increasingly
suspected to play a determinant impact in the formation of deep pressure
ulcers. In vivo observations of such deformations are complex to obtain.
Previous studies only provide global measurements of such deformations without
getting the quantitative values of the loads that generate these deformations.
To study the role that shearing loads have in the aetiology of heel pressure
ulcers, an MR-compatible device for the application of shearing and normal
loads was designed. Magnetic resonance imaging is a key feature that allows to
monitor deformations of soft tissues after loading in a non-invasive way.
Measuring applied forces in an MR-environment is challenging due to the
impossibility to use magnetic materials. In our device, forces are applied
through the compression of springs made in polylactide. Shearing and normal
loads were applied on the plantar skin of the human heel by means of an
indenting plate while acquiring MR images. The device materials did not
introduce any imaging artifact and allowed for high quality MR measurements
permitting to identify the deformation of the internal components of the heel.
The obtained subject-specific results are an original data set that can be used
in validations for Finite Element analysis and therefore contribute to a better
understanding of the factors involved in pressure ulcer development.
