Although we might want them to last a lifetime, it’s important to be aware that an artificial knee joint is only ever a temporary solution. That is not down to the prosthesis itself, but because the ageing process continues and can have a significant impact on the stability of the artificial joint. Nowadays, we expect the average prosthesis to last for at least ten to fifteen years. Patients who have had an artificial knee joint inserted at a young age should expect to have another replacement or revision operation later in life. However, given the remarkable advances in both surgical techniques and the development of new artificial joints, this is highly feasible. There are several factors that may negatively impact the lifespan of an artificial knee joint. Ultimately, these lead to a loosening of the artificial knee joint, which results in increased exertion-induced pain and an unsteady gait. In the advanced stage, this requires a revision of the prosthesis.
Exertion
The mechanical causes that negatively impact the lifespan of an artificial joint include increased stress on the joint, as well as deterioration of the original anchoring of the joint in the bone. The activities you partake in play a decisive role in over-exerting the joint. The more active you are and, above all, the more sports you partake in that apply pressure to the joint, the more the anchorage of the lower leg component will be stressed by the artificial joint. Excessive strain can also be the result of suboptimal placement of the artificial joint. Furthermore, the original anchorage of the artificial knee joint in the bone can deteriorate slowly due to advancing osteoporosis, or quickly due to a fall-induced fracture. Both cases lead to a loosening of the artificial knee joint.
Infections
Infections lead to activation of the immune system, causing inflammation and weakening the anchorage. They threaten the integrity of the artificial knee joint throughout the patient’s life. Bacteria can enter the bloodstream via mucous membranes or wounds in the skin, as well as through lung or bladder infections. These bacteria can then settle in the artificial knee joint, where they multiply and cause infection. What makes this so insidious is that it is often a long time before such an infection becomes apparent. Eventual symptoms include severe pain and swelling.
Allergies
Over the course of life, patients can develop an allergy to the prosthesis. The immune system defends itself against the foreign object, which is made from stainless steel (nickel, chromium, cobalt and molybdenum), or to the cement used to adhere it to the bone. This leads to a non-infectious inflammation of the artificial joint, which causes the joint to loosen.
Where any new exertion- or movement-induced pain occurs in the artificial knee joint and does not subside after a short time, advice should definitely be sought from an experienced knee specialist.