On the Mechanical Function of Marrow in Long Bones

Abstract

Hydraulic strengthening, viscous interaction between marrow and trabecular bone, and viscous resistance by the marrow to shear, appear not to occur in long bones when subjected to non-destructive axially applied compressive loads. These conclusions are based on the following observations. Firstly, volumetric measurements suggest that long bones deform in a way that maintains a near constant volume. Hence the mechanism by which ‘hydraulic strengthening’ could operate seems not to exist. Secondly, with little or no volume change, no significant movement between the marrow and the adjacent trabecular bone is likely to occur. The only mechanism by which the marrow could function mechanically would be by its own viscous resistance to shear deformation. As marrow is near liquid at 37°C (with a measured viscosity of 67 × 10-3 Pa s) this ‘resistance’ is shown to be negligible, even when calculated using values most favourable to the production of large shear forces.