RESUMEN

Entender el desgaste prematuro en reemplazos articulares debido a una lubricación deficiente, que puede resultar en valores de fricción altos, es un tema amplio e intrincado de abordar. Además, si el lubricante es el fluido sinovial, los mecanismos de lubricación que ocurren son aún más complejos de develar. En este artículo se revisa el estado de conocimiento actual de la lubricación sinovial, así como las características reológicas del fluido lubricante. Asimismo, se mencionan algunas técnicas experimentales y métodos numéricos con los que se ha estudiado el problema de la lubricación. En algunas simulaciones numéricas de la lubricación en reemplazos articulares no se considera el efecto del esfuerzo cortante del líquido sinovial ya que se asume que tiene un comportamiento newtoniano, sin embargo, otras investigaciones han demostrado que al asumir un comportamiento no newtoniano el proceso de lubricación se afecta significativamente. Con todo esto, incorporar todos los factores que pueden afectar la lubricación en reemplazos articulares, en simulaciones numéricas hasta la fecha es un reto. A través de diversas investigaciones se buscan nuevos materiales, diseños y técnicas de análisis que permitan incrementar la vida útil de los implantes para así reducir las cirugías de revisión(AU)

derstanding premature wear in joint replacements due to poor lubrication, which can result in high friction values, is a broad and intricate topic to address. In addition, if the lubricant is the synovial fluid, the lubrication mechanisms that occur are even more complex to unveil. This article reviews the current state of knowledge on synovial lubrication, as well as the rheological characteristics of the lubricating fluid. It is also made a mention of some experimental techniques and numerical methods with which the problem of lubrication has been studied. In some numerical simulations of lubrication in joint replacements the effect of the shear stress of the synovial fluid is not considered since it is assumed to have a Newtonian behavior; however, other research has shown that by assuming a non-Newtonian behavior the lubrication process is significantly affected. With all this, incorporating all the factors that can affect lubrication in joint replacements, in numerical simulations to date is a challenge. Through various investigations, new materials, designs and analysis techniques are sought to increase the useful life of implants in order to reduce revision surgeries(AU)

Asunto(s)

RESUMEN

The effect of surface texturing on the performance of biocompatible ultra-high molecular weight polyethylene (UHMWPE) as a bearing material has been investigated using the kinematic range of motions reported for a knee-joint replacement. An experimental apparatus consisting of a ball and a disk rotating independently from each other was used to compare the performance of UHMWPE textured versus plain surfaces, under different combinations of sliding and rolling motion, better known as sliding-to-rolling ratio (SRR). Performance was evaluated through the coefficient of traction of a tribosystem comprising a steel ball on a flat UHMWPE disk and distilled water at 36°C, acting as lubricant. A square array of cavities with diameter D=0.397mm and center-to-center spacing of 1.5D was machined on UHMWPE disks. The experimental design considered two levels for cavity depth, D and D/2, and two for the applied load, 17 and 25N. The SRR was varied from 1 to 11% and the mean speed range was set from 5 to 55mm/s, covering the kinematics and contact pressure conditions of a sauntering cycle on a knee-joint replacement. Stribeck curves of the plain and textured surfaces were obtained and compared against one another. The results demonstrate that the proposed surface pattern reduces the coefficient of traction of the tribological system for the 17N load in the entire kinematic range explored, while for the 25N load the effects were more noticeable at low mean speed and SRR, corresponding to the beginning of motion.

Asunto(s)