Total knee arthroplasty, or knee replacement, provides long-term pain relief and improved mobility for most patients. Failure occurs when the artificial joint, or implant, significantly degrades or its function diminishes, requiring further medical intervention. While most implants function well for decades, recognizing the warning signs of failure is important for ensuring timely and successful treatment.
Identifying Acute and Chronic Pain
Pain is often the first and most common indicator that a knee replacement may be failing, but this discomfort must be distinguished from normal post-operative soreness. The key difference lies in the pattern and timing of the pain, especially if it returns after an initial period of feeling well. Pain that begins subtly and increases gradually, often years after the original surgery, may signal aseptic loosening.
This chronic pain is typically felt deep in the joint and worsens significantly with activity, such as standing up or putting weight on the leg. The discomfort may also manifest as a noticeable ache that disrupts sleep, which suggests mechanical issues like the implant becoming loose from the bone. Aseptic loosening is often caused by microscopic debris from the plastic components wearing down, which then triggers a biological reaction that degrades the bone holding the implant in place.
Urgent Signs of Infection
A periprosthetic joint infection (PJI) is a complication that requires immediate medical attention, presenting with distinct inflammatory and systemic signs. Acute infection can appear soon after surgery or even years later, characterized by a sudden onset of severe pain, redness, and warmth around the surgical site. This type of infection may also involve a fever, chills, and the draining of pus or other fluid from the wound.
Delayed or chronic infections can be more subtle, sometimes presenting without dramatic systemic symptoms like high fever. Signs of a chronic low-grade infection may include persistent, unexplained fatigue and ongoing, low-level pain that does not resolve. The knee may feel stiff or mildly swollen, even in a joint that had previously functioned without issue for months or years.
Mechanical Dysfunction and Instability
Signs of mechanical dysfunction relate to the movement and physical integrity of the implant, often indicating component wear, misalignment, or ligament issues. Instability is a frequent symptom, where the knee feels unreliable, wobbly, or gives way unexpectedly during walking or standing. This sensation of the knee slipping can be caused by the ligaments surrounding the joint being too loose or by a component being positioned incorrectly.
A significant restriction in the knee’s range of motion is another sign of mechanical failure, causing the joint to become excessively stiff and unable to fully bend or straighten. Patients may also begin to notice new or worsening auditory signs coming from the joint, such as grinding, clicking, or popping noises. These sounds can be a physical manifestation of the plastic insert wearing out or the metal components rubbing against each other due to poor alignment.
Next Steps for Evaluation
Anyone who experiences a significant return of pain, new mechanical issues, or signs of infection should contact their orthopedic surgeon immediately. Early diagnosis is important for achieving the best possible outcome. The evaluation typically begins with a thorough physical examination and standard X-rays, which can help determine if the implant components have loosened from the bone.
The medical evaluation also includes blood tests to check for specific markers of inflammation, such as the C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR). If an infection is strongly suspected based on these initial results, the next step is often a joint aspiration. This procedure involves withdrawing a small amount of fluid from the knee for laboratory testing. These diagnostic steps help the medical team pinpoint the exact cause of the failure before determining the appropriate treatment plan.