Knee replacement surgery, also known as knee arthroplasty, is a widely performed medical procedure aimed at alleviating pain and restoring mobility in individuals with damaged knee joints. This surgery involves removing the worn or diseased sections of the knee and replacing them with artificial components. The primary objective is to create new, smooth joint surfaces, allowing for improved movement and a reduction in discomfort. This intervention can improve a person’s ability to perform daily activities like walking or climbing stairs, often difficult due to conditions like osteoarthritis.
Understanding the Replacement Components
The artificial components used in a total knee replacement are designed to mimic the natural joint’s function and typically consist of three main parts. The femoral component, which caps the end of the thighbone (femur), is usually made of a metal alloy, such as cobalt-chromium. This component is curved to replicate the natural shape of the femur and allow for smooth gliding.
The tibial component, placed on the shinbone (tibia), is often a flat, metal tray made from titanium or cobalt-chromium alloy. This tray is designed to fit onto the resected top surface of the tibia. A plastic insert, typically made of ultra-high molecular weight polyethylene, is then placed on top of this metal tray, serving as the new cartilage surface that articulates with the femoral component.
The third component, when used, is the patellar component, which replaces the back surface of the kneecap (patella). This part is usually a dome-shaped piece of polyethylene. These components are secured to the bone using surgical cement, although some designs feature porous surfaces that allow bone to grow into them.
Viewing a Replaced Knee on X-ray
When a knee replacement is viewed on an X-ray, the artificial components appear different from the natural bone. The metal parts, such as the femoral and tibial components, show up as bright white, dense structures because they absorb X-rays. This contrast allows for clear visualization of their position and alignment.
The polyethylene plastic insert appears faint or translucent on an X-ray, as plastic is less dense than metal and bone. Its presence is indicated by the space it occupies between the metal components. X-rays taken after surgery help surgeons verify that the components are correctly aligned and securely positioned.
Regular X-rays are also used over time to monitor the implant and check for loosening of the components from the bone, wear in the plastic insert, or changes in the alignment. The clarity of the metal components on X-ray aids long-term follow-up.
External Appearance After Surgery
Following knee replacement surgery, the external appearance of the knee will show a visible surgical scar. This incision is typically located on the front of the knee, running vertically down the center or slightly to one side. The length of the scar can vary, depending on the surgical approach and the individual’s anatomy.
Initially, the knee will appear swollen and may show bruising around the incision site, which is a normal response to surgery. The skin surrounding the incision may also be discolored, appearing red or purple. These temporary changes diminish over several weeks to months as the body heals.
As healing progresses, the scar will gradually flatten and fade in color, transitioning from a darker or reddish hue to a lighter, less noticeable line. While the scar will be a permanent mark, its prominence reduces over the first year. The knee regains a more natural contour once the initial post-operative swelling has resolved.