The purpose of a knee replacement is to replace a diseased or damaged knee to restore pain-free movement in the joint. The surgery involves the bones, ligaments, muscles, cartilage and bursa that form the knee. You can expect complete healing without complications and recovery from surgery in about 6 months. Before you begin, it might be helpful to review normal knee anatomy and how a normal knee should work.
The Artificial Knee Joint (prosthesis)
There are two main types of artificial knee replacement prosthesis—cemented and uncemented. Both types are widely used. In many cases, a combination of the two types are used. The kneecap, or patellar, part of the prosthesis is usually cemented into place. The choice to use a cemented or uncemented prosthesis is usually made by the surgeon based on your age and lifestyle, and your surgeon’s experience.
Each prosthesis has four parts:
- The femoral component is metal and replaces the end of the femur, the groove where the kneecap slides. The femur is commonly called the thighbone. It is the largest bone in the body.
- The tibial component replaces the end of the tibia—commonly called the shinbone. The tibial component is made up of the plastic spacer which provides a weight-bearing surface and the metal tibial tray that is fitted directly onto the bone. The plastic used is very tough and very slick – so slick and tough that you could ice skate on a sheet of the plastic without much damage to the plastic.
- The patellar component replaces the surface on bottom of the patella. The “top” of the kneecap is the part you can feel through your skin. The “bottom” is the on the other side, and slides up and down in the femoral groove when you bend or straighten your leg.
A cemented prosthesis is held in place using an epoxy type cement that attaches the metal to the bone. An uncemented prosthesis has a fine mesh of holes on the surface that allows the bone to grow into the mesh and attaches the prosthesis to the bone. During the operation, trial components—the same size as the actual components used for your knee—will be tested for stability, range of motion and tracking of the kneecap.
The Knee Replacement Operation
Replacing the knee begins with making an incision on the front of the knee to allow access to the knee joint.
Preparing the Femur
Once the knee joint is entered, a special cutting tool is placed on the end of the femur. This special tool ensures that the bone is cut keeping the proper alignment to the leg’s original angles – even if the arthritis has made you bowlegged or knock-kneed. Several pieces of diseased bone are cut away from the end of the femur so that the artificial knee can be attached.
Preparing the Tibial Bone
Then, the top of the tibia is cut using another cutting tool that also ensures proper alignment.
Preparing the Patella
The undersurface of the kneecap is removed.
Frontal View of Prepared Knee Bones
This is what the prepared surfaces look like viewed from the front. The patella has been moved to allow you to see the knee.
Placing the Femoral Component
The femoral component is then fitted on the femur. In the uncemented type of femoral component, the prosthesis is held on the end of the bone because the end of bone has a taperd cut. The metal prosthesis is made to almost exactly match the taperd cut of the bone. Fitting the femoral component onto the end of the bone holds the component in place by friction. In the cemented component, an epoxy cement is used to attach the metal prosthesis to the bone.
Placing the Tibial Component (metal tray)
The metal tray that holds the plastic spacer is attached to the end of the tibia. The metal tray is either cemented into place, or held in place with screws if the component is the uncemented type. The screws hold the tray in place until the bone grows into the porous coating. The screws are left in the bone and are not removed.
Placing the Tibial Component (plastic spacer)
The plastic spacer is attached to the metal tray of the tibial component. If the plastic spacer wears out it can be replaced if the rest of the prosthesis is in good condition – a so called retread.
Placing the Patellar Component
The patellar button is usually cemented into place behind the patella.
The Completed Knee Replacement
Xray from the side compared with illustration of knee prosthesis.
Xray from the front compared with illustration of knee prosthesis.
Model of knee anatomy with knee prosthesis in place.
The illustrations on this page are used with permission by Medical Multimedia Group, 308 Louisiana Avenue, Libby, Montana 59923. MMG holds the copyright on their images.
Total Knee Replacement: a guide to surgery and recovery
Table of Contents
- Knee Replacement
- Visit with Orthopedic Surgeon
- Getting Ready for Surgery
- Making Arrangements for Surgery
- Your Hospital Visit
- Recovery at Home
- Regaining Knee Strength and Motion
- Knee Replacement Surgery
- Complications of Knee Replacement Surgery