Biomechanical analysis of cemented implant fixation and application to buffered implant fixation

Abstract

Arthroplasty, which is the operation that replaces a damaged joint with the artificial implant, is one of the most frequently operated orthopedic surgeries. Up to now, many kinds of implants have been developed and used. However, implant fixation methods are categorized into two basic types: cemented and cementless. Also in cemented type, there are two kinds of concept according to surface finish: polished and rough. However, current implants have short longevity because of the stress shielding, wear debris, micromotion and so on. In this study, the problems of current implant fixation methods were investigated and the failure cause was analyzed in a biomechanical point of view. First, the effect of stem surface roughness was investigated in cemented implant fixation. For that, the axisymmetric simple model was developed and interface micromotions were measured in vitro. In axisymmetric simple model, polished taper stem sustained more load than rough stem because polished taper stem transferred more compressive load to bone interface. According to Hoffman’s criteria, compressive load prevents the shear failure at the interface. Otherwise, excessive hoop stress of polished stem can induce the failure of cement mantle. For in vitro measurements, small and light sensors were custom-made using straingages to measure accurate interface motion. The interface micromotions were detected at the all interfaces. Even the cement-bone interface, which was considered well interlocked, showed some micromotion. Also, small amount of cracks were found at the cement mantle. However, the differences in the micromotion and cracks between the polished stem and the matt-finished stem were not significant. Next, the finite element analysis of current implant fixation methods was performed to understand more completely the biomechanics of implant system. The polished cemented fixation could be taper-locked. The polished implant was subsided into cement so that the compressive stre...