Which specific parts of the bones are removed during TKA?

During TKA, the damaged articular cartilage and a thin layer of underlying subchondral bone are precisely removed from the medial and lateral femoral condyles, the medial and lateral tibial plateaus, and, if resurfaced, the posterior surface of the patella.

Are all ligaments removed during total knee replacement?

The Anterior Cruciate Ligament (ACL) and menisci are almost always removed during TKA. The Posterior Cruciate Ligament (PCL) may be removed or preserved depending on the implant design, but the Medial and Lateral Collateral Ligaments (MCL, LCL) are meticulously preserved.

What replaces the structures removed during a total knee replacement?

The removed structures are replaced with prosthetic components: a metal femoral component, a metal tibial tray with a polyethylene insert, and often a polyethylene button for the patella.

Why is it important for rehabilitation to know what structures are removed or preserved?

Understanding which structures are removed or managed is vital for rehabilitation as it dictates how stability is achieved (relying on prosthetic design and surrounding muscles), how preserved ligaments are protected, and how strength training progresses for incised and repaired muscles and tendons.

What structures are removed in total knee replacement?

Q: Is the entire knee joint removed during a total knee replacement?

No, Total Knee Arthroplasty (TKA) is a resurfacing procedure where only the damaged articular cartilage and a small amount of underlying bone from the femur, tibia, and sometimes the patella are removed, not the entire knee joint.

What structures are removed during total knee replacement?

During a total knee replacement (Total Knee Arthroplasty or TKA), the primary structures removed are the damaged articular cartilage and a small amount of underlying bone from the ends of the femur (thigh bone), tibia (shin bone), and often the posterior surface of the patella (kneecap).

Understanding Total Knee Arthroplasty (TKA)

Total Knee Arthroplasty (TKA) is a surgical procedure designed to alleviate severe knee pain and restore function in individuals suffering from conditions like osteoarthritis, rheumatoid arthritis, or post-traumatic arthritis. It's crucial to understand that TKA is fundamentally a resurfacing procedure, not a complete removal of the entire bone. The goal is to replace the diseased or damaged joint surfaces with prosthetic components, allowing the knee to move smoothly and pain-free.

Key Structures Addressed in TKA

The core problem addressed in TKA is the degradation of articular cartilage, the smooth, slippery tissue that covers the ends of bones within a joint, allowing them to glide effortlessly against each other. When this cartilage wears away, bone-on-bone friction occurs, leading to pain, stiffness, and reduced mobility. During TKA, this damaged cartilage, along with a minimal amount of the underlying subchondral bone, is precisely resected to prepare the bone for the prosthetic implants.

The knee joint is composed of three main compartments:

Medial Compartment: The inner side of the knee (between the medial femoral condyle and medial tibial plateau).
Lateral Compartment: The outer side of the knee (between the lateral femoral condyle and lateral tibial plateau).
Patellofemoral Compartment: The front of the knee (between the patella and the trochlear groove of the femur). In a total knee replacement, all three compartments are typically addressed.

The Femoral Component

The distal end of the femur forms the upper part of the knee joint.

Structures Removed: The damaged articular cartilage from the medial and lateral femoral condyles (the rounded ends of the femur) is removed, along with a precise, thin layer of the underlying subchondral bone. Bone spurs (osteophytes) that may have formed are also removed.
Prosthetic Replacement: A metal femoral component, typically made of cobalt-chromium or titanium alloy, is shaped to mimic the natural contour of the femoral condyles. This component is cemented or press-fit onto the resected bone surface.

The Tibial Component

The proximal end of the tibia forms the lower part of the knee joint.

Structures Removed: The damaged articular cartilage from the medial and lateral tibial plateaus (the flat top surface of the tibia) is removed, along with a thin layer of the underlying subchondral bone. This creates a flat surface for the tibial implant.
Prosthetic Replacement: The tibial component consists of two parts:
- A metal tray (often titanium alloy) that is cemented or press-fit onto the resected tibial surface.
- A polyethylene insert (a durable plastic liner) that snaps into or is fixed to the metal tray. This insert acts as the new articular cartilage, providing a smooth bearing surface for the femoral component to glide against.

The Patellar Component (Patellar Resurfacing)

The patella, or kneecap, glides in a groove on the front of the femur.

Structures Removed: If the cartilage on the posterior (back) surface of the patella is significantly damaged, it is resurfaced. The damaged cartilage and a small amount of underlying bone are removed from the back of the patella.
Prosthetic Replacement: A polyethylene button (a dome-shaped plastic component) is cemented onto the resected surface of the patella. This provides a new smooth surface for the patella to articulate with the femoral component.
Note: Patellar resurfacing is not performed in every TKA. The surgeon's decision often depends on the extent of patellar cartilage damage and their surgical philosophy.

Structures Typically Not Removed (But May Be Modified)

While specific damaged surfaces are removed, many crucial knee structures are carefully preserved or managed:

Collateral Ligaments (Medial Collateral Ligament - MCL, Lateral Collateral Ligament - LCL): These ligaments, located on the sides of the knee, are vital for stability. They are meticulously preserved during TKA. The surgical approach may involve incising the joint capsule and some soft tissues around them, but the ligaments themselves are kept intact.
Posterior Cruciate Ligament (PCL): The PCL is a strong ligament within the knee that prevents the tibia from sliding backward excessively. Its fate during TKA depends on the implant design:
- PCL-retaining designs: These implants are designed to work with a preserved PCL.
- PCL-sacrificing designs: The PCL is removed in these cases, and the implant's design (often with a "post and cam" mechanism) provides the necessary stability. Most modern TKAs are PCL-sacrificing to allow for greater range of motion and easier surgical technique.
Anterior Cruciate Ligament (ACL): The ACL is almost always removed during TKA. Its position and function are incompatible with the design of most total knee prostheses, and its removal provides necessary surgical access.
Menisci: The medial and lateral menisci (C-shaped cartilage shock absorbers between the femur and tibia) are typically removed entirely during TKA. Their function is effectively replaced by the polyethylene insert of the tibial component, and they are often damaged in arthritic knees.
Joint Capsule and Synovial Membrane: Portions of the joint capsule (the fibrous sac enclosing the joint) and synovial membrane (the lining of the capsule that produces lubricating fluid) are incised or trimmed during surgery to gain access to the joint. However, the majority of these structures remain and are repaired at the end of the procedure.
Muscles and Tendons: Muscles (e.g., quadriceps, hamstrings) and their tendons (e.g., patellar tendon) are incised or retracted to allow the surgeon access to the knee joint. They are not removed but are carefully repaired at the conclusion of the surgery to facilitate post-operative recovery and strength.

The Goal: Resurfacing, Not Replacement

Understanding what structures are removed during a total knee replacement clarifies that the procedure is not a complete amputation or removal of the entire knee joint. Instead, it's a precise surgical technique focused on resurfacing the damaged load-bearing surfaces with durable prosthetic materials. This targeted approach allows for the preservation of essential ligaments and soft tissues, which are crucial for the stability and function of the newly implanted joint.

Implications for Post-Surgical Rehabilitation

For fitness enthusiasts, personal trainers, and student kinesiologists, knowing precisely which structures are removed or managed during TKA is vital for designing effective rehabilitation programs. For example:

The absence of the ACL and often the PCL means that the stability of the new knee relies heavily on the prosthetic design and surrounding muscles.
Preservation of collateral ligaments emphasizes their role in mediolateral stability and guides exercises to protect them.
The integrity of the quadriceps and hamstring muscles, which were incised and repaired, dictates the progression of strength training.

A thorough understanding of these anatomical changes allows for a more informed and scientifically grounded approach to recovery, optimizing outcomes for individuals undergoing total knee replacement.

Total Knee Arthroplasty (TKA) is a resurfacing procedure that replaces damaged joint surfaces with prosthetic components, rather than removing the entire knee joint.
The primary structures removed are the damaged articular cartilage and a small amount of underlying bone from the ends of the femur, tibia, and often the posterior surface of the patella.
Prosthetic components, including metal for the femur and tibia, and durable polyethylene for the tibia and patella, are used to create new smooth bearing surfaces.
Crucial structures like the Medial and Lateral Collateral Ligaments, as well as muscles and tendons, are typically preserved, though the Anterior Cruciate Ligament and menisci are almost always removed.
A precise understanding of which structures are removed or managed during TKA is essential for designing effective post-surgical rehabilitation programs.

Total Knee Replacement: Structures Removed, Preserved, and Post-Surgical Considerations