A total knee replacement is a surgical procedure that replaces a damaged knee joint with artificial components. The goal is to alleviate pain and restore function for individuals with severe knee arthritis or other debilitating conditions. This operation can improve quality of life by enabling a return to normal daily activities with greater ease.
Pre-Surgical Knee X-Rays
X-rays are fundamental in assessing a knee’s condition before surgery. For a knee requiring a total replacement, these images reveal signs of advanced osteoarthritis. One prominent feature is joint space narrowing, where the cartilage that cushions the bones has worn away, causing the femur (thigh bone) and tibia (shin bone) to move closer together. This is often described as a “bone-on-bone” appearance.
In addition to reduced joint space, X-rays of an arthritic knee show osteophytes, or bone spurs. These are bony growths that develop along the edges of the joint as the body attempts to repair damaged cartilage. The images may also highlight bone structure deformities, such as a varus (bow-legged) or valgus (knock-knee) alignment, which contribute to uneven wear on the joint.
The Knee Implant Components
A total knee implant has several parts that resurface the ends of the bones to replicate the function of a natural knee. The materials are chosen for durability and biocompatibility, meaning they are well-tolerated by the body. The total weight of these components is between 15 and 20 ounces.
The femoral component is a curved, metal piece that fits over the end of the femur, often made from a scratch-resistant cobalt-chromium alloy. It is grooved to allow the kneecap to glide smoothly. The tibial component, or tibial tray, is a flat metal platform that covers the top of the tibia and is constructed from titanium or cobalt-chromium.
A polyethylene spacer fits between the femoral and tibial components. This plastic insert acts as the new cartilage, providing a smooth surface for the metal parts to move against. In some cases, a patellar component, a dome-shaped piece of polyethylene, is used to resurface the back of the kneecap, though this is not always necessary.
Post-Surgical Knee X-Rays
Following a total knee replacement, X-rays are taken to confirm the correct placement and alignment of the implant components. The metal femoral and tibial components are distinctly visible, showing how they have replaced the damaged bone and cartilage. The space between these metal parts, which appears as a gap on an X-ray, is occupied by the radiolucent polyethylene spacer.
The alignment of the implant is a focus of the post-operative assessment. An anteroposterior (front-to-back) view shows the tibial component should be perpendicular to the long axis of the tibia, while the femoral component is placed at a slight angle. A lateral (side) view helps ensure the components are positioned correctly for proper flexion and extension. These post-operative X-rays serve as a baseline for future comparisons.
The Surgical Incision and Scar
The surgical incision is made on the front of the knee and is about 4 to 6 inches in length, though the exact length can vary depending on the surgical technique and the patient’s anatomy. Immediately after the procedure, the incision is covered by a sterile dressing to protect it from infection.
Initially, it is common to experience swelling, bruising, and redness around the area, which will gradually subside. The incision line matures into a scar that will fade and become less noticeable over the course of a year. Protecting the new scar from sun exposure is important, as UV rays can cause it to darken.