Bone marrow pressure changes under an inflatable tourniquet

Theoretical calculations suggest that under a limb tourniquet, the pressure at the bone/tissue interface is greater than it is more peripherally. The central bony core must be incompressible for this hypothesis to be correct. Experiments designed to measure the intramedullary pressure confirm that this pressure does not rise at tourniquet pressures above the systolic blood pressure. It has also been suggested that shear stresses are the most likely cause of nerve damage under a tourniquet but this depends on the conversion of the tissue under compression into a fibro-elastic solid. This is likely to occur when all fluid has been driven out. From the experiments such a fluid shift does not seen to occur via the intramedullary cavity but it must nevertheless occur at an early stage of rising tourniquet pressure, probably by fluid shift through the veins proximal and distal to the tourniquet.