Reasons for Revision Total Knee Surgery
Patients requiring revision of a total knee replacement do so for loosening, implant failure or infection. Because the prosthetic components of an artificial joint are not living tissue, they have no way of replenishing themselves when they become worn, like the normal joint is capable of doing. Therefore, the wear that takes place with every step remains. After years of wear, the implants eventually fail. The primary mode of failure is implant loosening at the interface between the implant or cement and the bone. This is caused by the body’s response to the millions of foreign particles produced by the friction at the bearing surface. These particles incite production of enzymes that essentially digest the bone at the interface. This is known as osteolysis. After a while, the implant is unsupported and loosening occurs. This process can be seen on x-rays.
Sometimes the implant bearing surface can simply wear down without loosening of the entire implant. Although this is a mode of failure, revision surgery can often be directed at replacing the bearing surface, that is, the polyethylene insert.
Another reason for revision surgery is mechanical problems with the implant itself. For example, if the knee cap dislocates, revision of the implants may be indicated. This may require readjustment of the implants or placement of a more constrained implant.
Finally, infection of the total knee is a reason for revision surgery. This is probably the most dreaded of complications. The reason for this is that infection is not easily treated and typically requires the implant to be removed. Removal of the implant is done because bacteria can adhere to the implant and “wall” themselves from antibiotics. The implant itself has no way of fighting the infection. Treatment consists of implant removal, placement of antibiotic cement and at least six weeks of intravenous antibiotics. After the knee is completely sterile, new knee components can be be reimplanted in the knee.