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Why does a knee need to be replaced?
As the cartilage around the joint of the knees wears away, the bone is increasingly damaged. Eventually, the ends of the bone will grind together — with no cartilage left at all. Pain, swelling and stiffness may result, and a replacement of the knee joint is often the only option.
There are several conditions which might contribute to the destruction of the cartilage. They are:
Osteoarthritis: Often referred to as the "wear and tear" arthritis, osteoarthritis is the most common reason why knees need to be replaced.
Rheumatoid Arthritis: With this disease, the tissue surrounding the joints is often inflamed; as a result, the cartilage slowly deteriorates.
Post-Traumatic Arthritis: Injury to the knee may cause permanent damage to the ligaments which will lead to an unstable knee. In time, a knee replacement may be considered, depending upon the severity of the damage.
Avascular necrosis: This condition results from an inadequate supply of blood to the bone end inside the joint; as a result, the cartilage wears away. Once it is gone, knee surgery is inevitable.
Misalignment of the Knee Joint: Some congenital conditions — such as "knock-knees" or "bow legs" — can result in excessive rubbing at an unusual angle in the joint. Over time, the damage will be enough to require a knee replacement.
When is a knee replacement done?
This is a decision made between the patient and the doctor, but pain usually becomes the main issue. Some tests may be required to rule out other possibilities; others will wait for as long as possible before having the surgery. It truly is a personal decision.
What are the parts of an artificial joint?
The patient and surgeon will most likely discuss the various options when a knee replacement is being considered. There are several options to consider, including whether or not it will be a partial or whole replacement.
Sometimes a total knee replacement is not required. There are three parts of the knee which can be replaced (see diagram 2 above):
- the patellar component
- the femoral component
- the tibial component
The replacement parts are usually made of metal or plastic.
What types of knee replacements are there?
Thus far, surgeons have developed several different types of replacements, and one can only guess what new technologies will occur in the future.
For now, here are four of the most common:
Non-Constrained: This is said to be a "highly successful" implant and the most common type. It needs to be done before the ligaments have completely worn away. The artificial components are not linked into the knee and therefore provide no stability — instead, the person's own ligaments maintain the knee's stability.
Semi-Constrained: If all the inner knee ligaments must be removed, then stability has to come from the device that is placed in the knee. Therefore, there is more stability built-in with this type.
Constraint or Hinged: These types are used when the knee is highly unstable and the ligaments are of no use at all. They are most often used with elderly people who have severely damaged knees, and these surgeries will not last as long as the other types.
Unicondylar Knee Replacement: This procedure replaces only half of the knee joint. It happens when damage is limited to only one side.
There are also two other decisions to make:
Cemented Procedure: This fixes the components of the implant to the bone with a grout-like cement which allows the implants to perfectly fit to the irregularities of the bone.
Non-cemented procedure: Components of the implant have a rough and porous surface which allows bone to grow into it; hence, no cement is required. This procedure is relatively new, and so studies on its success or failure are few and far between.
Is there "life" after knee replacement?
Of course! Joint replacement operations have proven to be a predictable and successful treatment, and function and quality of life are often greatly improved afterwards. In fact, after joint replacement, athletic and recreational activities often increase.
However, there are guidelines and protocols that you should follow to be sure that you do not do too much too soon. You may never do high-impact aerobics again, but after healing and doing specific exercises to strengthen the muscles that surround the joint, you will probably be able to do more than you ever expected to!
Among the most common activities recommended after a knee replacement and healing and strengthening of muscles have occurred are 3:
- stationary bicycling
- dance/ballroom dancing
- doubles tennis
- low-impact aerobics
- lawn bowling
So keep your options open, talk to your doctor, and together make the decision when and if a knee replacement is the right decision for you.
Thanks to the two textbooks: Special Populations by On the Edge Fitness Education and Exercise and Arthritis by Stephanie Harris and Gwen Hyatt.
Other related articles (about joints and joint replacements):
- Exercise and Arthritis
- The Hip Joint
- Hip Replacement
- Is the old wives' tale true: Does your arthritis forecast tomorrow's weather?
- Joints and Exercise
- The Knee Joint
- The Shoulder Joint
- The Wrist and the Ankle
I am a BCRPA-certified fitness instructor in Vancouver, BC. I teach four classes at the West End Community Centre in Vancouver, BC, mostly designed for the older adult. The Inevitable Disclaimer: Everything published here expresses only my opinion, based on my training and research. What you do with the information is entirely your own responsibility. I am not liable for any injury you suffer that seems to be related to anything you read here. Always consult your doctor before beginning an exercise program. For other articles, return to the table of contents.