Knee replacements work by replacing damaged areas of the knee joint with metal and plastic components that allow the joint to function normally without pain, according to OrthoInfo. Knee replacements are typically performed on joints damaged by arthritis or injury.
The knee joint is formed where the thighbone (femur) conjoins with the kneecap (patella) and shinbone (tibia), explains OrthoInfo. Where these bones meet their surfaces are covered with articular cartilage, a smooth tissue allowing them to move freely against each other. C-shaped wedges of tissue called the menesci rest between the femur and tibia acting as a buffer to absorb impact. The rest of the knee joint is covered by the synovial membrane that lines the surfaces and produces lubricating fluid, virtually eliminating friction in the knee joint. Ligaments connect the leg muscles to the bones.
When the bones or ligaments of the knee are damaged by injury or arthritis, cartilage breaks down and friction occurs in the joint resulting in pain, stiffness and difficulty of movement, states OrthoInfo. During knee replacement surgery, the damaged cartilage at the ends of the leg bones is removed and replaced by metal implants. The patella is usually resurfaced with a plastic button. A plastic spacer is then inserted between the metal implants to replace the menisci. The artificially surfaced joint operates without friction like a normal, healthy knee.