Although the failure rate is low, knee replacements do not last forever. There are two main reasons for a revision knee replacement with the most common being infection, which can cause early loosening of the knee replacement. This usually occurs in the first couple of years after the initial operation and is often due to an infection at the time of the initial surgery.
The other main reason for failure is the loosening of the knee replacement. This generally occurs several years after initial operation and can be due to a mechanical failure of the knee replacement. In some early knee replacement designs, the plastic part of the tibial component became worn and fragmented after approximately eight to ten years. Newer designs have considerably better durability but, eventually, even these will show signs of wear.