Abrasive Wear of Ceramic,Metal,and UHMWPE Bearing Surfaces from Third-Body Bone,PMMA Bone Cement,and Titanium Debris

The debris generated by the progressive wear of total joint replacement (TJR) devices is considered a primary cause of osteolysis, bone resorption, and premature failure of artificial hips and knees. The vast majority of this debris originates from the UHMWPE articulating surfaces caused by tribological interaction with the opposing metal or ceramic surface and hard particulates contained in the sinovial fluid. Entrapment of third body debris, such as cortical bone, PMMA cement, and titanium debris, between the articulating surfaces can cause abrasion of both the hard bearing surface and the UHMWPE. The propensity for abrasive wear is dependent on the relationship between the hardness of the third-body debris and the hardness of the bearing surfaces. To gain a better understanding of this relationship and its effect on wear, the abrasive wear behavior of several metal and ceramic bearing surfaces was characterized in terms of the hardness of both the third-body debris and the metal or ceramic substrate. The effects of abrasion and increased surface roughness of the metal or ceramic surfaces on wear of the UHMWPE was also determined. In addition, the amount of UHMWPE wear was quantified in terms of the amount (particles/ml) of titanium fretting-type debris contained in solution.

The results of this investigation showed the resistance to abrasive wear of the metal and ceramic bearing surfaces to increase with increasing surface hardness. Bone debris, PMMA cement, and titanium debris produced visible abrasion of all metal surfaces including nitrogen ion implanted Ti-6AI-4V. The ceramic bearing surfaces showed no evidence of abrasion and produced the least amount of UHMWPE wear. The wear of UHMWPE sliding against Co-Cr-Mo was found to increase with increasing levels of 1.48 μm titanium debris added to the wear test solution. The rate of UHMWPE wear increased rapidly for concentrations of titanium debris in the test solution exceeding about 10⁵ particles/mi. These test results suggest that third-body particles, both large and small, are capable of causing increased abrasive wear of UHMWPE, and that abrasion of the hard bearing surfaces will occur if the hardness of the third-body debris exceeds the hardness of the metal or ceramic bearing surface.