Total Knee Arthroplasty (TKA): What Is Removed, Replaced, and Preserved

What is removed during a TKA?

During a Total Knee Arthroplasty (TKA), or total knee replacement, the damaged articular cartilage and a thin layer of the underlying bone from the ends of the femur (thigh bone), tibia (shin bone), and often the patella (kneecap) are precisely removed and resurfaced with prosthetic components.

Understanding Total Knee Arthroplasty (TKA)

Total Knee Arthroplasty (TKA) is a highly effective surgical procedure designed to alleviate severe knee pain and restore function in individuals suffering from debilitating conditions such as osteoarthritis, rheumatoid arthritis, or post-traumatic arthritis. Contrary to a common misconception, a TKA does not involve the complete amputation of the knee joint or the removal of entire bones. Instead, it is a meticulous resurfacing procedure where only the diseased or damaged portions of the bone and cartilage are excised and replaced with artificial implants.

The Primary Components Removed and Resurfaced

The core objective of a TKA is to remove the worn-out, pain-generating surfaces of the knee joint and replace them with smooth, durable prosthetic components. The specific structures targeted for removal and resurfacing include:

• Damaged Femoral Condyles: The lower end of the femur, which forms the upper part of the knee joint, has two rounded prominences called condyles. In a TKA, the damaged articular cartilage and a small, precise amount of the underlying subchondral bone from these condyles are removed. This prepares the bone for the application of a metal femoral component, which is shaped to replicate the natural curvature of the femoral condyles. This component is typically made of cobalt-chromium or titanium alloy.

• Damaged Tibial Plateau: The upper end of the tibia, which forms the lower part of the knee joint, has a relatively flat surface known as the tibial plateau. The worn-out cartilage and a thin section of the underlying bone from this surface are precisely resected. This prepares the tibia for a metal tibial tray, which is a flat or slightly sloped component usually made of titanium. Upon this metal tray, a polyethylene (medical-grade plastic) insert is placed. This plastic insert acts as the new smooth bearing surface, allowing the femoral component to glide freely, mimicking the function of healthy cartilage.

• Damaged Patella (Kneecap) Undersurface: The patella, or kneecap, is a small, sesamoid bone that glides in a groove on the front of the femur. If the articular cartilage on the undersurface of the patella is significantly damaged and contributing to pain, it may also be resurfaced. This involves removing the worn cartilage and a small amount of bone from the back of the patella and replacing it with a polyethylene button that is cemented into place. It's important to note that patellar resurfacing is not always performed; the decision depends on the extent of the damage, the surgeon's preference, and the patient's specific condition.

What is NOT Removed (and Why)

While significant portions of the joint surfaces are addressed, it's crucial to understand what remains intact:

• Majority of the Bones: The vast majority of the femur, tibia, and patella bones are preserved. Only the very ends of the bones, where the joint surfaces are located, are prepared for the implants.
• Ligaments (Mostly): The collateral ligaments (medial collateral ligament - MCL, and lateral collateral ligament - LCL) on the sides of the knee, which provide stability, are typically preserved. The fate of the cruciate ligaments (anterior cruciate ligament - ACL, and posterior cruciate ligament - PCL) depends on the specific type of TKA performed. Many modern TKAs are "PCL-sacrificing" or "PCL-retaining," meaning the PCL may or may not be removed. The ACL is almost always removed due to the nature of the cuts required.
• Muscles and Tendons: The major muscles (e.g., quadriceps, hamstrings) and their associated tendons surrounding the knee joint are not removed. They are carefully moved aside during surgery to allow access to the joint and are then repositioned. These structures are vital for post-operative strength and mobility.

The Role of Implants

The implants used in TKA are meticulously designed to replicate the natural anatomy and biomechanics of the knee joint. They are durable, biocompatible materials chosen for their strength, wear resistance, and ability to integrate with bone. The combination of metal and plastic creates a low-friction articulation, allowing for smooth, pain-free movement.

Why is TKA Performed?

The primary indication for TKA is severe joint degeneration, most commonly from:

• Osteoarthritis: "Wear-and-tear" arthritis, where the cartilage gradually erodes over time.
• Rheumatoid Arthritis: An autoimmune disease causing chronic inflammation and joint destruction.
• Post-Traumatic Arthritis: Arthritis developing after a significant knee injury, such as a fracture or ligament tear.

When conservative treatments (e.g., physical therapy, medications, injections) no longer provide adequate pain relief or functional improvement, TKA becomes a viable option to restore quality of life.

Post-Operative Considerations

Following a TKA, a structured rehabilitation program is essential. This typically involves physical therapy focused on restoring range of motion, strength, and functional mobility. Understanding that the surgery involves precise removal and replacement of joint surfaces helps patients appreciate the importance of post-operative care in optimizing the longevity and performance of their new knee.

In summary, a Total Knee Arthroplasty is a sophisticated procedure that selectively removes and replaces only the diseased portions of the knee joint, preserving healthy bone and soft tissues wherever possible to facilitate a return to an active, pain-reduced lifestyle.