Three-dimensional tissue deformation in subcutaneous tissues overlying bony prominences may help to explain external load transfer to the interstitium.

Anesthetized, carefully positioned, female, weanling, white-haired pigs were used to test the hypothesis that (1) interface pressure, the pressure between the skin and an external load, can be used to predict the interstitial fluid pressure over the wings of ilia and the last dorsal spinous process and (2) three-dimensional tissue deformation of the interstitium under the load could partially explain how the external load is transferred at that site. When a 4 or 8 kg load was distributed over the hips of the pigs, the interface pressures over the ilia were approximately 145 and 207 cm H2O, respectively. Approximately 28% of this pressure was transferred to the tissue, resulting in an increase in interstitial fluid pressure of approximately 39 cm H2O for the 4 kg load and 60 cm H2O for the 8 kg load. However, over the spinous process, about 42-43% of the load was transferred to the interstitium. Subcutaneous tissue marker movement occurred along the gamma and theta spherical coordinate but no significant tissue marker movement along the phi coordinate. The latter indicates no significant twisting of the tissue while the former demonstrates three-dimensional shearing. There were also indications of tissue creep since the markers continued to move with constant loading.