A patellofemoral replacement (PFR), or kneecap replacement, is a specialized type of partial knee replacement. This surgical procedure focuses on resurfacing only the damaged surfaces of the patellofemoral joint, which is the area where the kneecap (patella) glides in a groove on the thighbone (femur). Its purpose is to alleviate pain caused by isolated arthritis located specifically behind the kneecap, while preserving the healthy cartilage, bone, and ligaments in the rest of the knee.
Individuals who typically undergo this procedure have arthritis confined to this single compartment of the knee, often experiencing pain when climbing stairs, squatting, or rising from a seated position. It is also considered for younger patients with advanced kneecap cartilage damage that has not responded to other treatments. By targeting only the affected area, a patellofemoral replacement aims to offer a less invasive alternative to total knee replacement for suitable candidates.
Expected Lifespan of Patellofemoral Replacements
Patellofemoral replacements are not considered a permanent solution, and their longevity can vary among individuals. Studies and clinical data provide insights into the typical survival rates of these implants over time.
Earlier studies on patellofemoral arthroplasty, particularly first-generation designs, reported survival rates where approximately 84% of implants were still functioning at 10 years, and about 69% at 20 years. More recent data from international joint registries indicates improved outcomes, with survival rates of around 90.30% at 5 years and 82.23% at 10 years. These figures suggest that a significant majority of patellofemoral replacements continue to perform well for a decade or more.
However, long-term survivorship does show a gradual decrease, with rates dropping to approximately 73.74% at 15 years and 72.68% at 20 years, based on pooled data. This indicates that some patients may require revision surgery as the implant reaches the end of its functional life. Continuous advancements in implant design and surgical techniques aim to enhance these longevity figures.
Factors Influencing Implant Durability
The longevity of a patellofemoral replacement is shaped by patient characteristics, the surgical execution, and the design and materials of the implant itself. Understanding these influences can provide a clearer picture of expected implant lifespan.
Patient-specific factors play a role. Younger patients tend to be more active, which can lead to increased wear and tear on the implant over a longer period. Higher body mass index (BMI) places greater stress on the knee joint, potentially accelerating the wear of implant components. Studies indicate that revision rates are higher in obese patients, highlighting the impact of sustained excessive load on the implant.
The precision of the surgical procedure also directly affects implant durability. Accurate placement and alignment of the implant components are essential for optimal function and to minimize uneven loading or premature wear. The surgeon’s experience and technique contribute to achieving this precise fit, which can influence the long-term success of the replacement.
Implant characteristics, including design and materials, are continuously evolving to enhance durability. Modern implant designs, for example, aim to better mimic the natural knee mechanics, reducing stress points and improving overall function. Materials like ultra-high molecular weight polyethylene for the kneecap component and cobalt-chrome or titanium alloy metals for the femoral component are engineered for wear resistance.
However, even with advanced materials, polyethylene wear remains a consideration, as microscopic particles can be generated over time. The method of implant fixation, typically involving bone cement, also contributes to stability, though aseptic loosening—where the implant detaches from the bone without infection—can occur.
Maximizing the Lifespan of Your Replacement
Patients can actively contribute to the long-term success of their patellofemoral replacement by adopting specific practices and lifestyle adjustments. These measures help minimize stress on the implant and promote overall joint health.
Adherence to a structured post-operative rehabilitation program is fundamental. This typically involves physical therapy sessions that focus on regaining full range of motion, strengthening the quadriceps muscles, and improving overall knee stability. Following the surgeon’s and physical therapist’s instructions regarding exercises, weight-bearing progression, and activity levels is important for proper healing and integration of the implant. Early, controlled motion and specific exercises like heel slides, quad sets, and patellar mobilizations are often prescribed.
Activity modification is another key aspect. Patients are generally advised to engage in low-impact activities such as walking, swimming, and cycling, which are gentler on the knee joint and help maintain fitness without undue stress on the implant. High-impact activities like running, jumping, heavy lifting, or sports involving sudden twisting and pivoting movements are typically discouraged, as they can accelerate wear and tear on the prosthetic components.
Maintaining a healthy body weight plays a significant role in prolonging the implant’s lifespan. Excess body weight increases the load across the knee joint, which can lead to accelerated wear of the plastic and metal components of the replacement. Effective weight management reduces this mechanical stress, thereby contributing to the implant’s durability.
Regular follow-up appointments with the orthopedic surgeon are also important to monitor the condition of the implant and the overall health of the knee. These visits allow the surgeon to identify any potential issues early and address them before they escalate.
Recognizing and Addressing Implant Failure
Even with the best care, a patellofemoral replacement may eventually reach the end of its functional life or encounter complications. Recognizing the signs of implant failure is important for timely intervention.
Common indicators of a failing patellofemoral replacement include increasing pain, which is often the most noticeable symptom and a frequent reason for early failure. Patients might also experience instability, swelling, stiffness, or changes in how they walk. Mechanical issues such as clicking, clunking, or the kneecap not tracking correctly (maltracking) can also signal a problem. In some cases, warmth and redness around the knee could suggest an infection.
Several factors can lead to implant failure. The most common reason for late failure is the progression of arthritis in other parts of the knee that were not initially replaced, affecting up to 42% of cases. Another significant cause is aseptic loosening, where the implant detaches from the bone without infection, accounting for around 13-14% of failures. This can sometimes be challenging to diagnose. Polyethylene wear, where the plastic component of the implant degrades over time, can also contribute to loosening.
Less common but serious causes include infection, which can occur at any point after surgery and manifest with increased pain, warmth, redness, or fever. Patellar maltracking, where the kneecap does not move properly in its groove, and issues related to the original surgical technique or trauma are also potential contributors to failure. When a patellofemoral replacement fails, it often necessitates further surgical intervention.
This next step typically involves revision surgery, which may mean replacing one or more components of the partial knee replacement or, more commonly, converting it to a total knee replacement. Total knee arthroplasty is the revision procedure in a significant majority of cases, highlighting its role as a comprehensive solution when a partial replacement no longer functions effectively. While revision surgery can successfully address the issues, it is generally more complex than the initial procedure and may have different outcomes.