knee parts diagram

Are there different kinds of knee implants?

Yes, there are several different types of knee replacements. All of them are variations of the basic design introduced more than 30 years ago, which is called the “total condylar posterior stabilized knee.” The choice of implants depends on factors such as the status of ligaments and the amount of deformity in the knee. Usually, we use a “high-flex” design that is safe for deep knee bending. The implants come in “gender-specific” versions engineered to match the knee anatomy of men and women. As new designs in total knee replacements are developed, we will adopt them in our practice only after carefully considering the advantages, safety and scientific merits of such designs.

What if I want a different brand of knee prosthesis?

Local surgeons and hospitals eager to get your business sometimes publicize new implants. Some of these newer designs are true improvements, while others are simply old designs with new packaging, gimmicks and slick marketing. If truly innovative implants are introduced, the odds are we have been using them well before they are released to community orthopaedic surgeons. If you have an interest or preference for a particular type or brand of knee implant, please let us know and we will explore the option together.

Can ceramic parts be used in knee replacements?

Yes – the advantage is the lower wear rate of ceramics when compared to metals. In the United States, ceramic knees are used on a limited basis since the Food and Drug Administration (FDA) has not approved them for general use. Several years ago, we conducted one of the few clinical trials in the country on ceramic knees.

Ceramic parts are useful in the rare cases of a true metal allergy in selected patients. Ceramic components will likely become more common in the future. At the time, ceramic materials in total knees are more common overseas. Balancing the very low wear rates of ceramics is the fact that we do not have enough scientific data from U.S. studies to support their routine use in total knee replacements as of yet.

Do you use the same model of knee implant for all knee replacements?

No. Each patient situation is unique and the type of implant chosen depends on many patient variables, including age, gender, weight, bone dimensions, ligament condition, bone quality, anticipated activity level and occupational history.

In older patients with weak and osteoporotic bone, for example, the best choice may be a cemented model supplemented by design features that support external knee ligaments. On the other hand, for a healthy young person with a physically demanding job, the ideal model may be an un-cemented total knee design that allows as much bone preservation as possible.

In patients who have had knee replacement in the past and are in need of repeat surgery, it is often necessary to use more complex models, to reconstruct deficient and missing bone. 

Are newer knee implants much different from old ones?

Yes, there are newer “high-flex” knee designs that allow greater safety during deep knee bending. There are also newer “gender-specific” total knees made to fit the anatomical differences in the knees of men and women. All knee replacement components we use incorporate these modern design features. As newer designs evolve and are approved by the FDA, we offer them to our patients. Other variations in total knee implants include a ceramic “oxinium” surface, the “rotating-platform” knee and other brands marketed by implant companies. Let us know if you have a preference, and we will help you make an informed choice.

Can I get a “golfer’s knee” implant?

If you prefer one kind of implant to the other, we can discuss your options. Keep in mind that no knee implant is better suited for golf or any other sport. Participation in activities such as golf is equally possible, and equally easy with any of the competing knee designs out there, whether or not they claim to be a “golfer’s knee.”

What about a custom knee replacement made just for my leg?

One of the newest innovations in knee replacement is the concept of custom-manufacture of knee implants that are made specifically to each patient’s size and unique anatomy. CT (computerized tomography) or MRI (magnetic resonance imaging) scan is used to determine the precise anatomy of the patient’s ankle, hip and knee. 

Are there other implants that are used to treat knee arthritis?

In unusual cases of knee arthritis and in relatively young patients, a shim-like device called the uni-spacer may be used. This device acts like a spacer to separate the worn-out knee surfaces and keep them from grinding against each other. Very few patients meet the criteria for this type of surgery and a uni-spacer is a temporary option best reserved for very young patients with knee arthritis.

In what cases do you use human tissue for knee replacement?

In rare cases, we use cadaver tissue for reconstruction of the extensor mechanism in selected knees. These are complex cases with previous trauma that has ruptured the quadriceps tendon in addition to causing arthritis of the knee. For the majority of knee replacements, no human tissue is ever needed.

How does the artificial knee joint get lubricated?

After a joint replacement, the artificial bearing gets its lubrication from synovial fluid, just like the natural knee joint. After surgery, the synovial lining re-forms and secretes synovial fluid. In cars, oil must be changed regularly, but in the body, the cells recycle synovial fluid. No external lubrication of the knee joint is ever necessary. In fact, any injections placed into your artificial knee joint increase the risk of infection.

Can patients become allergic to the knee replacement parts?

The metals used in artificial knees are alloys of cobalt-chromium and titanium. The bearing portion of the joint is made of a high-grade, wear-resistant plastic. The metal-plastic bearing combination is the most common type used in knee replacement implants worldwide. These metals have been used in humans for many decades and millions of patients with very successful results. Allergic reaction to artificial knee parts is virtually unheard of and is not a routine clinical concern.

In the extremely rare case of a true metal allergy verified by testing, we have material science options to replace a knee without exposure to titanium, nickel or cobalt-chrome, which are the usual metals used in standard knee replacements. In other words, metal-allergic patients can still get a knee replacement.

What actually moves inside an artificial knee joint?

In an artificial knee joint, highly polished cobalt-chromium metal moves against a very durable plastic spacer to allow movement. This bearing is lubricated by your body’s own synovial fluid, which is constantly replenished by living cells. The power to move the artificial knee, once implanted in your body, comes from your own muscles. That is why the condition of your muscles affects how quickly you recover after any type of knee surgery, including a total knee replacement.

Learn more about knee replacement surgery at MU Health Care.