Knee arthroplasty/

Introduction
A painful knee can severely affect your ability to lead a full, active life. Over the last 25 years, major advancements in artificial knee replacement have improved the outcome of the surgery greatly. Artificial knee replacement surgery (also called knee arthroplasty) is becoming increasingly common as the population of the world begins to age.
This guide will help you understand
Anatomy
What is the normal anatomy of the knee?
The knee joint is formed where the thighbone (femur) meets the shinbone (tibia). A smooth cushion of articular cartilage covers the end surfaces of both of these bones so that they slide against one another smoothly. The articular cartilage is kept slippery by joint fluid made by the joint lining (synovial membrane). The fluid is contained in a soft tissue enclosure around the knee joint called the joint capsule.
The patella, or kneecap, is the moveable bone on the front of the knee. It is wrapped inside a tendon that connects the large muscles on the front of the thigh, the quadriceps muscles, to the lower leg bone. The surface on the back of the patella is covered with articular cartilage. It glides within a groove on the front of the femur.
Rationale
What does the surgeon hope to achieve?
The main reason for replacing any arthritic joint with an artificial joint is to stop the bones from rubbing against each other. This rubbing causes pain. Replacing the painful and arthritic joint with an artificial joint gives the joint a new surface, which moves smoothly and without causing pain. The goal is to help people return to many of their activities with less pain and with greater freedom of movement.
The Artificial Knee
There are two major types of artificial knee replacements:
• cemented prosthesis
• uncemented prosthesis
Both are still widely used. In many cases a combination of the two types is used. The patellar (kneecap) portion of the prosthesis is commonly cemented into place. The decision to use a cemented or uncemented artificial knee is usually made by the surgeon based on your age, your lifestyle, and the surgeon's experience.
Each prosthesis is made up of three main parts.
The tibial component (bottom portion) replaces the top surface of the lower bone, the tibia. The femoral component (top portion) replaces the bottom surface of the upper bone (the femur) and the groove where the patella fits. The patellar component (kneecap portion) replaces the surface of the patella where it glides in the groove on the femur.
The femoral component is made of metal. The tibial component is usually made of two parts: a metal tray that is attached directly to the bone, and a plastic spacer that provides the slick surface. The plastic used is so tough and slick that you could ice skate on a sheet of it without damaging the material much. The patellar component is usually made of plastic as well. In some types of knee implants, the patellar component is made of a combination of metal and plastic.
A cemented prosthesis is held in place by a type of epoxy cement that attaches the metal to the bone. An uncemented prosthesis has a fine mesh of holes on the surface that allows bone to grow into the mesh and attach the prosthesis to the bone.
The Operation
To begin the procedure, the surgeon makes an incision on the front of the knee to allow access to the joint. Several different approaches can be used to make the incision. The choice is usually based on the surgeon's training and preferences.
Once the knee joint is opened, a special positioning device (a cutting guide) is placed on the end of the femur.