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Knee Replacement: Frequently Asked Questions

Posted in: Education

Learn the difference between partial and full knee replacements, what to expect in recovery time, and more.


What is arthritis and why does my knee hurt?
The knee joint has a layer of smooth cartilage on the lower end of the femur (thighbone), the upper end of the tibia (shinbone) and the undersurface of the kneecap (patella). This cartilage serves as a cushion and allows for smooth motion of the knee. Arthritis is a wearing-away of this smooth cartilage. Eventually it wears down to bone. Rubbing of bone against bone causes discomfort, swelling and stiffness.

What is a total knee replacement?
A total knee replacement is really a cartilage replacement with an artificial surface. The knee itself is not replaced, as is commonly thought, but rather an artificial substitute for the cartilage is inserted on the end of the bones. This is done with a metal alloy on the femur and plastic spacer on the tibia and kneecap (patella). This creates a new smooth cushion and a functioning joint that does not hurt.


What is a partial (or unicompartmental) knee replacement?
A unicompartmental knee is a partial knee replacement. It is not as common as a total knee replacement. The “partial” knee replacement, as it is commonly called, has a smaller, less invasive incision.

The knee joint has the following three compartments:

  1. Medial (inner)
  2. Lateral (outer)
  3. Patellofemoral (kneecap)

A partial knee replacement is a resurfacing of only the diseased portion of the knee joint. Literally, half of the knee is replaced. If two or more compartments are damaged, then the partial knee may not be the best option for that particular patient. A total knee replacement may be the necessary and better option. About seven people out of 100 are good candidates for a unicompartmental knee replacement.

What are the advantages of having a partial knee replacement?
The advantages of having a partial knee replacement are:

  • Shorter recovery time
  • Less pain than other knee reconstruction surgeries
  • Better motion
  • Near normal function
  • Fewer complications
  • Lasts as long as a total knee replacement

Can a partial knee replacement be converted into a total knee replacement if needed in the future?
Yes, since a unicompartmental reconstruction preserves much of the patient’s natural knee, it can be converted to a total knee replacement in the future. Additionally, unlike most total knee replacements, the anterior and posterior cruciate ligaments (ACL and PCL) are saved in a partial knee replacement. These ligaments stabilize the knee during movement.


What types of materials are used?
The materials are designed to enable the joint to move just like your normal joint. Several metals are used, including stainless steel and alloys of cobalt, chrome and titanium. The plastic material, polyethylene, is durable and wear resistant. A bone cement may be used to anchor the prosthesis into the bone. Some joint replacements are implanted without cement.

What are the results of joint replacement?
Ninety-five percent of patients achieve good to excellent results with relief of discomfort and significantly increased activity and mobility.

Why do they fail?
The most common reason for failure is loosening of the artificial surface from the bone. Wearing of the polyethylene liner may also result in the need for a new liner.

When should I have joint replacement surgery?
The goal is to relieve pain in the joint caused by the damage done to the cartilage. The pain may be so severe, a person will avoid using the joint, therefore, weakening the muscles around the joint and making it even more difficult to move. Your orthopedic surgeon will ask you to decide if your discomfort, stiffness and disability justify undergoing surgery. There is no harm in waiting if conservative, non-operative methods are controlling your discomfort. Total joint replacement is considered when other treatment options do not relieve your pain and disability. Based on your history, exam and X-rays, your surgeon will determine if you are a good candidate for joint replacement.

Am I too old for joint replacement?
Age is not a problem if you are in reasonable health and have the desire to continue living a productive, active life. You may be asked to see your personal physician for his/her opinion about your general health and readiness for surgery.

How long will my new joint last and can a second replacement be done?
We expect most knees to last more than 20 years. However, there is no guarantee and 10-15 percent may not last that long. Younger patients may need a second replacement or a revision of the implant components. Materials and surgical techniques are continually improving.