Effect of pressure on bone cement stiffness. An in vitro study

Twenty-two canine femora were injected with PMMA cement at pressures varying between 0.2 and 1.3 MPa. Sections cut from the femora were tested in bending in several planes and under axial loading. Cement penetration was determined for each section. The bending and axial stiffness values were correlated with the cement penetration values. Both bending and axial stiffness were related linearly to penetration and nonlinearly to the cement intrusion pressure. The stiffness values increased with the intrusion pressure: slowly at low pressures, rapidly at medium pressures, slowly again at higher pressures, and leveling off at about 1.2 MPa. The 75 per cent of the maximum bending and axial stiffness values were achieved with a cement intrusion pressure of 0.55 MPa.