Total Knee Replacement (TKR) is a successful procedure for relieving pain and restoring function in patients with severe knee arthritis. Like any mechanical implant, the artificial joint (prosthesis) can eventually fail. When a primary total knee replacement no longer functions correctly, knee revision surgery is required. This second operation removes the original components and implants a new prosthesis to address the underlying mechanical or biological issues that caused the initial failure.
The Need for Revision Surgery
Total knee replacements are highly durable. Approximately 95% of implants function well for at least ten years, and 85% remain successful at the twenty-year mark. Despite this reliability, a small percentage of patients will eventually require a revision procedure. Only about 10% of patients need a revision within the first two decades.
Revision surgery is prompted by noticeable signs of implant failure. Common indicators include persistent or worsening pain, especially with weight-bearing activities, suggesting the implant has become loose. Patients may also experience decreased joint function, such as stiffness, reduced range of motion, or a sensation that the knee is unstable or “giving way.” Swelling, warmth, or a new limp can also indicate prosthesis failure.
Aseptic Loosening: The Most Common Cause
The most frequent reason for TKR revision surgery is aseptic loosening. This condition is the failure of the implant to maintain a secure bond with the surrounding bone tissue, occurring without a bacterial infection. It is a mechanical and biological process that typically manifests many years after the primary surgery.
The primary mechanism driving aseptic loosening is osteolysis, the breakdown of bone tissue. This bone loss is triggered by the body’s inflammatory reaction to microscopic wear particles generated from the plastic component (usually ultra-high molecular weight polyethylene). Friction causes tiny debris to shed into the joint space, which the immune system attempts to clear.
This response involves specialized cells called macrophages, which release chemical signals that stimulate bone-resorbing cells (osteoclasts). This process gradually erodes the bone surrounding the implant, weakening the fixation interface between the prosthesis and the skeleton. Once the bone support is compromised, the implant begins to move slightly under stress, leading to the pain and instability characteristic of aseptic loosening.
Other Significant Causes of Failure
While aseptic loosening is the most common long-term issue, other factors necessitate revision surgery. Periprosthetic joint infection (PJI) is a serious complication occurring when bacteria colonize the implant surfaces. Since bacteria can form a protective biofilm, the foreign material makes the infection difficult to treat with antibiotics alone. PJI often requires a complex, two-stage revision procedure before a new prosthesis is implanted.
Another significant cause of failure is instability, accounting for a substantial percentage of revision cases. Instability can result from improper positioning or alignment of components during the initial surgery, or from an imbalance in the surrounding ligaments. This leads to a persistent feeling of the knee “giving out” or excessive joint movement, causing pain and difficulty walking.
Mechanical degradation of the implant material, particularly the ultra-high molecular weight polyethylene (polyethylene wear), can also cause failure. Although modern manufacturing has reduced this complication, the plastic liner between the metal components can still wear out or suffer fatigue damage. This breakdown can lead to component damage or contribute to the wear particles that cause osteolysis and subsequent aseptic loosening.
What Revision Surgery Involves
Revision total knee replacement is a more intricate and demanding procedure than the original TKR. It requires extensive preoperative planning and often takes longer to perform. The surgeon must first carefully remove the old, failed components and any cement used for fixation, which is challenging due to bone ingrowth or cement bonding.
Bone loss resulting from osteolysis or removal of the original implant is a frequent complication that must be addressed to provide a stable foundation for the new prosthesis. Surgeons may use specialized techniques like bone grafting to fill defects, or utilize metal wedges and specialized components to reconstruct the joint. The new revision implants often feature longer, thicker stems that extend deeper into the bone for secure fixation.
When a periprosthetic joint infection causes failure, the procedure is typically performed in two stages. The first stage involves removing the infected components and temporarily placing an antibiotic-loaded cement spacer. After systemic antibiotic treatment clears the infection, the patient returns for a second surgery to implant the permanent prosthesis. Recovery from revision surgery is generally more extended and complex than the primary replacement, often requiring specialized rehabilitation.