Optimizing the bone cement-implant interface by hydrolysis-resistant conditioning of the metal surface

Abstract

The hydrolytic degradation of the implant-cement interface has to be seen as the main reason for aseptic loosening of cemented total hip replacements. Therefore, a new method of conditioning the metallic surface was developed in order to achieve a hydrolytic-resistant bound stability between the implant and bone cement. Preliminary experimental data on test bodies are presented here. The metallic surface of 6 pairs of cylindrical test bodies each (CoCr-alloy, circular testing surface with O 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 initial 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, 37 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. 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 unchanged high mechanical stability with tensile bond strength values of 37.0 MPa (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). With reservation as to further in vitro and in vivo investigations the increased hydrolytic stability of the metal-cement-bound of surface-conditioned CoCr-alloy test bodies promises an improvement of the long-term stability of cement total joint replacements.