Optimization of the implant-cement interface by hydrolytic resistant conditioning of the metallic surface.

Purpose: The hydrolytic degradation of the implant-cement interface has to be seen as the main reason for aseptic loosening of cemented total hip repl acements. Therefore, a new method of conditioning the metallic surface was developed in order to achieve a hydrolytic-resistant bound stability betwee n the implant and bone cement. Preliminary experimental data on test bodies are presented here. Method: The metallic surface of 6 pairs of cylindrical test bodies each (CoCr-alloy, circular testing surface with circle divide 6 mm) were conditioned by the method of silicoating/silanisation to gain a covalent coupling with the applied bone cement. In order to examine the ini tial stability and the hydrolytic resistance of the metal-cement compound, these pairs of surface-conditioned test bodies (SCT) as well as a reference series of surface-unconditioned test bodies (SUT) were immersed for 0, 30, 90, 150 days (d) in moisture environment (physiological saline solution, 3 7 degrees C) after coupling with bone cement. The adhesive strength of the test bodies-(bone cement-compounds) were determined by tensile tests on an universal testing machine (Typ Z030, Zwick, Ulm) with gimbal suspension. Re sults: At time 0 d (that was without immersion of the test bodies) the mean maximum tensile bond strength of the SCT-cement-compounds was 39,5 MPa (SD +/- 4,7 MPa) and that of the SUT-cement-compounds 37,1 MPa (SD +/- 7,3 MPa ) (p = 0,575). After immersion the tensile bond strength of the SUT-cement- compounds significantly decreased to an average of 13,5 MPa (SD +/- 2,7 MPa ) (30 d), 10 MPa (SD +/- 1,7 MPa) (90 d) and 12,3 MPa (SD +/- 1,4 MPa) (150 d) (p < 0,01). In contrast, the SCT-cement-compounds showed a nearly uncha nged high mechanical stability with tensile bond strength values of 37,0 MP a (SD +/- 4,9 MPa) after 30 d, 36,1 MPa (SD +/- 5,0 MPa) after 90 d und 30, 2 MPa (SD +/- 4,7 MPa) after 150 d (p > 0,01). Conclusions: With reservatio n as to further in vitro and in vivo investigations the increased hydrolyti c stability of the metal-cement-bound of surface-conditioned CoCr-alloy tes t bodies promises an improvement of the long-term stability of cement total joint replacements.