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.
For most knee replacements, a custom implant tailored to each patient is the best option. The company that makes these is Conformis (www.conformis.com). This technology is the best design today. We have also used the Zimmer brand of knee implants (www.zimmer.com, and www.pacewithlife.com) (Note: No implant company pays Dr. Bal to promote or implant its products and no commercial entity has contributed, in any way, to the preparation of this guide.)
Yes. We have actual parts in the clinic that you can see and hold, as well as videos and animations on this website.
New implants are sometimes hyped up by local surgeons and hospitals eager to get your business. Some of these newer designs are true improvements, while others are simply old designs with new packaging, gimmicks, and slick marketing. As a new design is introduced and marketed by the orthopaedic implant industry, we will present it with an unbiased discussion on our website, www.hipandknee.com. If truly innovative implants are introduced, the odds are that 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.
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.
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 will support external knee ligaments. On the other hand, for a healthy young person with physically demanding job, the ideal model may be an uncemented 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. To see some of the different models we use, view the video related to this subject on our website, www.hipandknee.com.
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 that 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.
As above, if you prefer one kind of implant over the other, we can discuss the 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.”
The newest, and in our opinion, most exciting innovation 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 or MRI imaging is used to determine the precise anatomy of the patient’s ankle, hip, and knee. These data are sent to a company called CONFORMIS (Boston, MA), where the metal and plastic pieces are custom-made for the patient in about 5-6 weeks, much like a tailor-made suit. The instruments used to implant the knee prosthesis are designed for a one-time use, specific to the patient, and are made of a biodegradable material. One neat package contains everything needed for the operation, and is unique for each knee joint, fitting only that one.
This technology, in use in our practice since early 2013, is truly innovative and reflects a meaningful step forward in knee replacement surgery. So far, our results show earlier and easier recovery for the patient, and x-rays that are beautifully precise in terms of rotation, alignment, and sizing. This technology incorporates all of our knowledge and design understanding in knee replacement, worldwide. It increases patient safety, promotes quality and consistency, ensures precision and a perfect fit every time, and therefore has our full support.
(Please interpret this information in light of a conflict, in that Dr. Bal serves as consultant surgeon for CONFORMIS, and is on a surgeon advisory and design team for this company. We do not receive any royalty or other payment to promote or implant CONFORMIS knee products, however, since the consulting activities concern other CONFORMIS technology platforms.)
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 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.
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, synovial fluid is recycled by the cells. 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.
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.
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.