Biomechanics of Natural and Artificial Joints

Summary

We investigated and compared biomechanics of natural and artificial joints. The most important functions of the joints rely on excellent lubrication and uniform distribution of impact loads on to the underlying bones. As to the lubrication, we measured dynamic changes of the joint space optically and verified the existence of fluid film lubrication in natural joints. From the aspect of fluid film lubrication, ultra high molecular weight polyethylene (UHMWPE) is not as good a material as polyvinyl alcohol hydrogel (PVA-H) and articular cartilage. The momentary stress transmitted through the specimens revealed that subchondral cancellous bones played the most important role and that UHMWPE had a higher peak stress and a shorter duration of sustained stress than articular cartilage and PVA-H, suggesting a worse damping effect. From the results of finite element method (FEM) analysis, intramedullary stem fixation might not avoid stress shielding. In artificial joints in the future, it is desirable to preserve as much subchondral cancellous bone as possible and to replace the involved joint surface with materials whose mechanical properties are similar to those of articular cartilage. We also reported biocompatibility, wear resistant properties of PVA-H, and attachment of this material to underlying bones. Although some problems still remain to be solved, PVA-H seems to be a very interesting and promising material which meets the requirements of artificial articular cartilage.