Wear Properties of UHMWPE in CHARITE َ Artificial Inter-vertebral Disc

Over the past three decades more than a half a million joint replacements have been performed. Several advances have been made to the design of the implants, but despite the large success of these procedures, loosening of the components and periprosthetic osteolysys often requires a revision surgery. In looking at what causes this, the wear of the UHMWPE articulation surface and the associated biological reactions to the wear debris have emerged as a major problem in total joint replacements. The main reason for wear testing is to determine the device durability, looking for potential failure modes such as fracture, or excessive wear that may lead to compromised function. The other reason is to try to predict the effect the device may have on the body. Neurotoxicity, inflammation, oncogenesis and osteolysis are all side effects that may be present when a device is implanted in the body and have been seen in cases with hip and knee replacement. In determining the durability of an implant you first must know the types of loads that the device will be exposed to. These can be taken from research done over the past several years (see Figure1). Different loading conditions and motion controls must also be considered when testing these implants. Debates continue on the most physiologically accurate method for setting up test parameters. Current testing has shown wear debris testing of the CHARITE artificial disc to be significantly lower than the artificial hip and knee implants under similar loading conditions. When a cross-path motion loading condition is compared to curvilinear motion loading condition it can be seen that there is also significantly more wear with a cross-path motion profile. The large discrepancy in the amount of wear that can be achieved based on a different motion profile is an important consideration in the design and further development of medical devices. For future development, there are several areas that will require research. The first is to look at the effects of sterilization methods of the UHMWPE on fatigue performance. The second is to try to gain a better understanding of loads that the body may undergo during daily activities. The third is to determine the most accurate method of testing devices concerning motion and loading parameters.