556 Acta Orthopaedica 2011; 82 (5): 553–558 Figure 3. A. Relationship between implantation period and bending strength. B. Relationship between implantation period and bending modulus. Figure 4. A. Relationship between implantation period and density. B. Relationship between density and bending strength. C. Relationship between density and bending modulus. Figure 5. A. Relationship between implantation period and porosity. B. Relationship between density and porosity. C. Relationship between porosity and bending strength. D. Relationship between porosity and bending modulus. retrieved specimens. As the porosity of cement is unlikely to change substantially after curing, the mechanical properties of the cement should remain stable. Discussion One of the factors that dictate the long-term stability of