A total knee replacement is widely considered a successful orthopedic procedure, offering substantial pain relief and restoring function for many years. However, like any mechanical implant, it can sometimes fail, requiring a subsequent operation known as revision surgery. Failure is medically defined as the necessity for an additional surgical procedure to address a complication with the implant or surrounding tissue. Recognizing the signs of a failing implant early is important, as prompt diagnosis and intervention lead to better patient outcomes.
Key Warning Signs of a Failing Implant
The most common indicator that a knee replacement is failing is the return or new onset of significant pain after a period of relief. This discomfort is often felt during weight-bearing activities, such as walking or standing. Chronic pain can also manifest while the leg is at rest or at night. Pain that returns months or years after the initial recovery period suggests a problem with the implant’s fixation or wear.
Patients may also report a sensation of instability, often described as the knee “giving out” or feeling loose. This weakness or inability to bear weight can result from poor soft-tissue balance or a mechanical issue with the prosthesis. Persistent swelling, redness, or warmth around the joint are indicators of inflammation or a potential infection.
New or worsened mechanical symptoms, such as clicking, grinding, or painful popping, suggest wear or improper alignment of the components. When the plastic spacer wears down, the metal parts may interact incorrectly, causing these noticeable sounds and sensations. A gradual decrease in the knee’s ability to move freely, or stiffness that worsens over time, is also a sign that the implant is no longer functioning optimally.
Common Causes of Knee Replacement Failure
The mechanisms that cause a knee replacement to fail are distinct from the symptoms a patient experiences. One frequent reason for failure is aseptic loosening, where the implant detaches from the bone without infection. This often happens years after the initial surgery as the bond between the implant and the bone weakens, sometimes due to the body’s reaction to microscopic wear particles.
The wear of the polyethylene component, the specialized plastic spacer, is a common catalyst for loosening. As this plastic wears down from friction, tiny debris particles are released into the joint. This triggers an immune response that can cause osteolysis, the breakdown of the surrounding bone, eventually leading to a loss of fixation.
Another cause is periprosthetic joint infection (PJI), which can occur shortly after surgery or years later due to bacteria traveling through the bloodstream. Infections are difficult to treat because bacteria can form a protective layer on the implant, challenging antibiotic effectiveness. Other structural issues, such as instability, component malalignment, or periprosthetic fracture, can also necessitate revision.
How Doctors Confirm Implant Failure
The diagnostic process begins with a physical examination and a review of the patient’s history, focusing on the nature and timing of symptoms. Imaging studies are the first step, starting with standard X-rays to look for specific signs of failure. The surgeon searches for evidence of component shifting or radiolucent lines, which are small gaps between the bone and the implant indicating loosening.
If X-rays are inconclusive, advanced imaging like a Computed Tomography (CT) scan or Magnetic Resonance Imaging (MRI) may be ordered. CT scans are useful for detailed three-dimensional views of bone structure and for planning revision surgery. MRIs provide better visualization of soft tissues, such as ligaments and tendons.
Laboratory tests are employed when infection is possible, focusing on inflammation markers in the blood. These include the Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP), which are often elevated with infection. The definitive test for infection is a joint aspiration, where fluid is drawn directly from the knee joint. This fluid is analyzed for cell count and cultured to identify the specific bacteria.
Revision Surgery and Treatment Paths
Once the specific cause of the implant failure is confirmed, treatment is planned. This may range from non-surgical management for minor issues to complex revision surgery. Non-surgical options are limited to managing pain and symptoms for non-mechanical failures, but most true implant failures ultimately require an operation. Revision surgery involves removing the failed components and replacing them with new, specialized implants.
The revision procedure is often more complex than the initial knee replacement because the surgeon must address any bone loss. This sometimes requires the use of bone grafts or implants with longer, stronger stems for support. The treatment path for failure due to infection is distinct and more involved than for aseptic loosening.
Infected cases typically require a two-stage revision. The first surgery removes the old implant and places a temporary antibiotic-loaded cement spacer in the joint. The patient then receives several weeks of intravenous antibiotics to eradicate the infection. The second surgery involves placing the new, permanent implant.
While a single-stage revision may be performed for less severe infections, the two-stage approach remains common for chronic cases. Recovery from a revision procedure is generally more prolonged and challenging than recovery from the original knee replacement. This often requires a longer period of rehabilitation.