Marx R, Faramarzi R, Jungwirth F, Kleffner B V, Mumme T, Weber M, Wirtz D C
Klinik für Zahnärztliche Prothetik, Lehr- und Forschungsgebiet Werkstoffkunde, Universitätsklinikum Aachen.
Z Orthop Unfall. 2009 Mar-Apr;147(2):175-82. doi: 10.1055/s-0029-1185456. Epub 2009 Apr 8.
For cemented hip prostheses, all requirements can be fulfilled by using forged Co/Cr/Mo stems. Co/Cr/Mo alloys, however, are contraindicated for allergy sufferers. For these patients, a cemented prosthesis made of titanium (alloy) would be indicated. Cemented stems from titanium (alloy), depending on the geometry of the prosthesis and its specific surface texture, however, may have loosening rates which are clinically not tolerable. In comparison to Co/Cr/Mo alloys, the greater roughness in conjunction with lesser abrasion resistance of titanium-based alloys leads to high loosening rates caused by abrasion. On the other hand, the greater surface roughness permits good mechanical retention of bone cement to the surface. Good mechanical retention enhances migration behaviour and reduces micromotions. However, there is no stable hydrolytic bond between bone cement and metallic surface; intermediate-term debonding between metal and bone cement is predictable. This debonding results in relative movements, consequently in wear particles which have their origin both from the rough metallic surface and from the PMMA cement. The roughness of the metallic surface operates as emery and with that, a rubbing wear from the PMMA.
For the above reasons, a low or moderate roughness is essential for easily abradable implants such as shafts made of titanium (alloy) because low roughness provides a fail-safe running function in case of debonding. Thus, one must allow for inappropriate migration behaviour accompanied by greater micromotions due to insufficient mechanical retention in the case of low roughness. This can be accomplished by a silicate layer coating applied to the metal shaft surface via electrochemical "ECD" or physical vapour deposition "PVD". For analysis, specimens (screws for pull-out, cones for push-out tests) were sand-blasted, so that roughnesses between Ra = 0.8 microm (Rz = 4 microm) and Ra = 2.0 microm (Rz = 9 microm) were generated.
The bond strengths observed in tensile tests for roughnesses of Ra = 1.7 mm were always well above 25 MPa for all periods of hydrolytic load. Therefore, the investigation shows that surfaces of moderate roughness (Ra = 1.7 microm), however coated, provide a steady retention. Cave-in and micromotions should widely be prevented.
The abrasion, which is a consequence of and reason for debonding and loosening at the same time, should be avoidable if the bonding of cement on the metallic shaft is stabilised with the help of a suitable chemical bond system.
对于骨水泥型髋关节假体，使用锻造钴/铬/钼柄可以满足所有要求。然而，钴/铬/钼合金对过敏患者禁用。对于这些患者，建议使用钛（合金）制成的骨水泥型假体。然而，取决于假体的几何形状及其特定表面纹理，钛（合金）制成的骨水泥柄可能具有临床上无法耐受的松动率。与钴/铬/钼合金相比，钛基合金更大的粗糙度以及更低的耐磨性导致由磨损引起的高松动率。另一方面，更大的表面粗糙度允许骨水泥与表面有良好的机械固位。良好的机械固位增强了移位行为并减少了微动。然而，骨水泥与金属表面之间不存在稳定的水解键；金属与骨水泥之间的中期脱粘是可预测的。这种脱粘会导致相对运动，进而产生磨损颗粒，这些颗粒既来自粗糙的金属表面，也来自聚甲基丙烯酸甲酯骨水泥。金属表面的粗糙度起到砂纸的作用，从而导致聚甲基丙烯酸甲酯产生摩擦磨损。
基于上述原因，对于易磨损的植入物，如钛（合金）制成的柄，低粗糙度或中等粗糙度至关重要，因为低粗糙度在脱粘情况下能提供故障安全运行功能。因此，在低粗糙度情况下，由于机械固位不足，必须考虑到会伴随更大微动的不适当移位行为。这可以通过经由电化学“ECD”或物理气相沉积“PVD”在金属柄表面施加硅酸盐层涂层来实现。为了进行分析，对试样（用于拔出试验的螺钉、用于推出试验的锥体）进行喷砂处理，从而产生介于Ra = 0.8微米（Rz = 4微米）和Ra = 2.0微米（Rz = 9微米）之间的粗糙度。
在拉伸试验中观察到，对于Ra = 1.7毫米的粗糙度，在所有水解加载时间段内，粘结强度始终远高于25兆帕。因此，研究表明，中等粗糙度（Ra = 1.7微米）的表面，无论是否有涂层，都能提供稳定的固位。应广泛防止塌陷和微动。
如果借助合适的化学键系统稳定骨水泥在金属柄上的粘结，那么作为脱粘和松动的结果及原因的磨损应该是可以避免的。
