The most common symptoms of a failed knee implant are pain, decrease in joint function, knee instability, and swelling or stiffness in the knee joint. Persistent pain and swelling can indicate loosening, wear or infection, and the location of the pain can be all over the knee (generalized) or in one particular area (localized). A decline in knee function may result in a limp, stiffness or instability. Patients who demonstrate these symptoms and signs may require revision joint surgery.