| Bone is a self-repairing structural material, which adapts its material properties, and shape in response to altered mechanical loading. The specific mechanism responsible for skeletal adaptation is not well understood. When cancellous bone is subjected to mechanical loading, bone marrow displacements occur within the bone matrix. This load induced bone marrow/matrix interaction in cancellous bone might play a role in skeletal adaptation. To study this bone marrow/matrix interaction, the basic parameters that characterize this phenomenon have to be well understood. Three parameters that characterize the fluid-flow properties of cancellous bone in the human calcaneus were studied. They are (1) the rheological properties of bone marrow obtained from the human calcaneus, (2) the permeability of cancellous bone harvested from different locations in the human calcaneus, and (3) the nature of pressures that occurred in the human calcaneus during physiological loading. The influence of shear rate on viscosity depended on the state of health of subjects, with some pathological marrow behaving like a non-Newtonian fluid and the normal yellow marrow as a Newtonian fluid. The average viscosity of yellow marrow in normal individuals at approximately 36°C was found to be 37.5 centipoise. Permeability in the calcaneus was dependent on the location of bone cores. In the calcaneus, the mediolateral bone cores offered the highest resistance to fluid flow. Comparing the micro-architectural measurements with permeability values revealed that permeability values were dependent on the presence of rods and plates. The calcaneus of cadaver feet displayed both positive and negative pressures during stimulated standing and toe off phase. The results from this study will help us understand the bone marrow/matrix interaction in the calcaneus during normal activities of daily living. |
