An in vitro study of hydraulic stiffening in cancellous bone

It was hypothesized that cancellous bone is a poroelastic material, and appropriate property data were obtained from the literature to formulate a three-dimensional poroelastic finite element model. Thirty-three cylindrical cancellous bone samples (bovine) were subjected to compressive cyclic strain excitation (triangle wave) with a maximum of 2000 /spl mu//spl epsi/. All specimens showed clear signs of time dependent material behavior: the force response lagged the displacement input in phase (/spl phi/=4.4/spl deg/-15.8/spl deg/), and contained a decaying transient term. The finite element model underestimated the transient behavior (/spl phi/=1.3/spl deg/-3.8/spl deg/) and predicted that less than 10% of bulk tissue stress was borne by the fluid. Decreasing the permeability value of the cancellous tissue was found to bring the model predictions into closer qualitative agreement with the experimental results, indicating the need for further study of this important parameter.