RELIABILITY OF PMMA BONE-CEMENT FIXATION - FRACTURE AND FATIGUE CRACK-GROWTH BEHAVIOR

Fracture mechanics tests were performed to characterize the fracture t oughness and fatigue crack-growth behaviour of polymethylmethacrylate (PMMA) bone cement, commonly used in joint replacement surgery. Compac t tension specimens of various thicknesses were prepared and tested in both air and Ringer's solution. Contrary to previous reports citing t oughness as a single valued parameter, the PMMA was found to exhibit r esistance-curve behaviour with a plateau toughness of similar to 0.6 M Pa m(1/2) in air, and similar to 2.0 MPa m(1/2) in Ringer's solution. The increased toughness in Ringer's solution is thought to arise from the plasticizing effect of the environment. Under cyclic loads, the ma terial displayed true mechanical fatigue failure in both environments; fatigue crack-growth rates, da/dN, were measured over the range simil ar to 10(-10) to 10(-6) m/cycle and found to display a power-law depen dence on the stress intensity range, Delta K. The cement was found to be more resistant to fatigue-crack propagation in Ringer's solution th an in air. Wear debris was observed on the fatigue fracture surfaces, particularly those produced in air. These findings and the validity of using a linear-elastic fracture mechanics approach for viscoelastic m aterials are discussed in the context of providing more reliable and f racture-resistant cemented joints.