RESUMEN
A three-axial, single-station hip joint simulator was designed and built for wear and friction studies on total hip prostheses. The design of the apparatus is described in detail. Continuous level walking is simulated. All three motion components, flexion-extension, abduction-adduction and internal-external rotation, are included. The motions are implemented electromechanically and the uniaxial load pneumatically. The load is measured continuously. For accurate measurement of wear, the apparatus has a loaded control joint, which also renders both the test and control joints self-centering, as they are loaded in series. The frictional torque of the test joint can be measured continuously throughout the wear test, which is an exceptional feature. Four tests of five million cycles each were completed using 32 mm diameter Co-Cr-Mo femoral heads and 5.6 mm thick, metal-backed, ultra-high molecular weight polyethylene acetabular cups as test specimens. Their wear and friction behaviour is described and discussed in relation to previous simulator studies and clinical observations. The lubricant was distilled water, maintained at body temperature. The wear of the cups was measured gravimetrically at intervals. The average wear rate was 3.9 mg/one million cycles, corresponding to 0.03 mm/year, and the average coefficient of friction was 0.01.
Asunto(s)
Articulación de la Cadera/fisiología , Prótesis de Cadera , Modelos Biológicos , Fenómenos Biomecánicos , Fricción , Humanos , Lubrificación , Ensayo de Materiales , Movimiento/fisiología , Tamaño de la Partícula , Polietilenos , Diseño de Prótesis , Falla de Prótesis , Rango del Movimiento Articular/fisiología , Estrés Mecánico , Temperatura , Soporte de Peso/fisiologíaRESUMEN
Ultra-high molecular weight polyethylene acetabular cups backed by Ti-6Al-4V acetabular shells were articulated against Co-Cr-Mo alloy, ion-implanted Co-Cr-Mo alloy, and zirconia ceramic femoral heads in a hip joint simulator. Three tests of three million walking cycles each were run with five different head-cup combinations. The wear of the cups was measured gravimetrically at half a million cycle intervals. When the thickness of the cup was 10.9 mm, the mean wear rate was 0.14 mm/year against 28 mm dia. Co-Cr-Mo heads and 0.09 mm/year against ion-implanted 28 mm Co-Cr-Mo heads. When the thickness of the cup was 7.0 mm, the mean wear rate was 0.04 mm/year against 28 mm zirconia heads, but when the thickness was 10.9 mm, no wear occurred against 28 and 32 mm zirconia heads. The results indicate that a significant reduction in the wear of the polyethylene cup can be expected if zirconia is used as the head material, instead of Co-Cr-Mo alloy or ion-implanted Co-Cr-Mo alloy. The diameter of the zirconia head, 28 vs. 32 mm, seems unimportant, but a cup thickness much below 10 mm may be disadvantageous.
Asunto(s)
Prótesis de Cadera , Acetábulo , Humanos , Polietilenos , Diseño de PrótesisRESUMEN
5 ultra-high molecular weight polyethylene acetabular cups articulated against alumina femoral heads for 35 million walking cycles in a hip joint simulator designed for wear tests of total hip prostheses. The specimens were from Protek, Biomet, Link, Howmedica and Thackray. In the Howmedica specimen, the wear was zero, and in Link and Thackray practically negligible. In Biomet, however, the wear was noteworthy and in Protek disastrous after 20 million cycles because in these 2 prostheses the head was attached to a titanium-alloy stem by taper-fit: titanium-alloy particles that were removed from the taper because of micromotion between the head and stem were entrapped between the head and cup, adhering to the head and making it rough, which led to severe abrasive wear of the Protek cup. It was worn through at 26 million cycles, the total wear being 3,170 mg. In Biomet, Link and Thackray, the total wear was 124, 5.3 and 17.6 mg, respectively. Polyethylene wear particles may lead to adverse tissue reactions and eventual loosening of the implant. The results indicate that by the use of alumina heads, polyethylene wear can be eliminated, but this advantage may be lost if the head is attached to a titanium-alloy taper.
Asunto(s)
Prótesis de Cadera/instrumentación , Ensayo de Materiales , Óxido de Aluminio , Prótesis de Cadera/métodos , Polietilenos , Diseño de Prótesis , Falla de PrótesisRESUMEN
Ultra-high molecular weight polyethylene acetabular cups of 5 different total hip systems (Müller, Mallory-Head, Lubinus, P.C.A. and Charnley-Elite) were worn on a new 5-station hip joint simulator. The cups articulated against modular metallic (stainless steel in Müller and Charnley-Elite, ion-implanted Ti-6Al-4V in Mallory-Head, and Co-Cr-Mo in Lubinus and P.C.A.) and modular alumina ceramic femoral heads for 3 million walking cycles. The mean wear rate of cups against alumina heads (range 0-5.7 mg/10(6) cycles, corresponding to 0-0.008 mm/year) was usually lower than against metallic heads (range 3.9-178 mg/10(6) cycles, corresponding to 0.005-0.24 mm/year). In the metal-head prostheses, the mean wear rate was highest against stainless steel heads, and lowest against ion-implanted Ti-6Al-4V heads. As the wear rates are compared with published clinical observations, it can be concluded that the hip joint simulator is capable of producing realistic wear rates; it is a useful instrument in the study of the wear behavior of new designs, materials, surface treatments and coatings prior to clinical trials. However, the taper-fit attachment of modular heads proved problematical, showing corrosion and wear at the conical head-spigot interface.