knee anatomy
Welcome to Skill Builders patient resource about Artificial Joint Replacement of the Knee.
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.
knee anatomy
This article will help you understand:
what your surgeon hopes to achieve with knee replacement surgery
what happens during the procedure
what to expect after your operation
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.
knee anatomy
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.
Related Document: Skill Builders Guide to Knee Anatomy
knee anatomy
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.
knee anatomy
Preparation
How should I prepare for surgery?
The decision to proceed with surgery should be made jointly by you and your surgeon. The decision should only be made after you feel that you understand as much about the procedure as possible.
Once you decide to proceed with surgery, several things may need to be done. Your orthopedic surgeon may suggest a complete physical examination by your regular doctor. This is to ensure that you are in the best possible condition to undergo the operation. You may also need to spend time with the physiotherapist who will be managing your rehabilitation after the surgery. The physiotherapist will begin the teaching process before surgery to ensure that you are ready for rehabilitation afterwards.
One purpose of the preoperative visit is to record a baseline of information. This includes measurements of your current pain levels, functional abilities, the presence of swelling, and the available movement and strength of each knee.
A second purpose of the preoperative physiotherapy visit is to prepare you for your upcoming surgery. You will practice some of the exercises used just after surgery. You will also be trained in the use of either a walker or crutches. (Whether the surgeon uses a cemented or noncemented artificial knee will determine how much weight you will apply through your foot at first while walking.) Finally, an assessment will be made of any needs you will have at home once you're released from the hospital.
knee anatomy
You may be asked to donate some of your own blood before the operation. This blood can be donated three to five weeks before the operation, and your body will make new blood cells to replace the loss. At the time of the operation, if you need to have a blood transfusion you will receive your own blood back from the blood bank.
Skill Builders provides services for physiotherapy in Barrie.
Surgical Procedure
What happens during the operation?
Before we describe the procedure, let's look first at the artificial knee itself.
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.
knee anatomy
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.
knee anatomy
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.
This cutting guide is used to ensure that the bone is cut in the proper alignment to the leg's original angles, even if the arthritis has made you bowlegged or knock-kneed. With the help of the cutting guide, the surgeon cuts several pieces of bone from the end of the femur.
The artificial knee will replace these worn surfaces with a metal surface.
Next, the surface of the tibia is prepared.
Another type of cutting guide is used to cut the tibia in the correct alignment.
Then the artificial surface of the patella is removed.
The metal femoral component is then placed on the femur. In the uncemented prosthesis, the metal piece is held snugly onto the femur because the femur is tapered to accurately match the shape of the prosthesis. The metal component is pushed onto the end of the femur and held in place by friction. In the cemented variety, an epoxy cement is used to attach the metal prosthesis to the bone.