Knee Surgery

Once you have an artificial knee, what will be different? Here are answers to common questions.

How do I know if I have a metal allergy to the knee part?

Orthopaedic implants are made of alloys of cobalt-chrome and titanium that have been implanted in millions of patients over the past three decades. Allergies to solid metal alloys are sometimes speculated, but are rarely seen in practice. Most instances of a painful knee after replacement have to do with a problem related to the surgery, or possibly an infection. A true metal allergy is extremely rare, and seldom encountered in clinical medicine.

What will weather changes feel like in the knee?

Some patients report increased pain and stiffness, or can feel changes in the weather after knee surgery, especially with an artificial joint. These sensations are not common though, and usually will disappear over one to two years after surgery. For the first couple of years, the bone adapts and grows around the metal prosthesis, and this bone activity probably leads to increased sensitivity to weather and pressure changes that some patients can feel in their joints.

What do I need to know about future dental work and other surgery?

Because you have an artificial knee joint in place, you must take care to protect it from infection. The same applies to any artificial implant in your body. Before having dental work (teeth cleaning, fillings, extraction or root canals) or certain medical procedures (colonoscopy, biopsy, endoscopies, etc.), you must take an antibiotic.

The antibiotic will help prevent bacteria from getting into the blood stream and thus into your knee. The odds of this happening are very rare, but the antibiotic can reduce this already small risk.

For routine dental prophylaxis following knee replacement surgery, antibiotics are required for your lifetime after the surgery.

What antibiotics are used to protect the prosthetic knee joint if I have dental work?

Cephalexin and amoxicillin are antibiotics commonly prescribed before and after dental work. You may take azithromycin or clindamycin if you are allergic to amoxicillin. You also may take any antibiotic recommended by the American Heart Association.

What other situations will I need antibiotics for, after the knee replacement?

Antibiotics given for other medical procedures may vary. Contact your doctor for advice if there is any doubt. Keep in mind that it will be necessary for you to be treated with a full course of antibiotics if you develop an infection such as an abscessed tooth, pneumonia, bronchitis, and skin or urinary infections.

If you cut your foot, or have broken skin on the leg, or infection in a toenail after a knee replacement, seek medical attention immediately. Ignoring a festering sore means that there is a risk the bacteria could migrate to the knee implant, resulting in a serious deep infection, even though it happens rarely.

Will the knee set off a metal detector at the airport?

Most likely, it will. Tell airport personnel that you have an artificial joint prior to entering the metal detector. Metal detection sensitivity at airports is highly variable, and it is impossible to say if a certain detector will set off the equipment. Your doctor or nurse will supply you with an implant identification card that you can carry to prove that you have metal knee replacement parts.

Can I have a MRI scan after knee replacement?

Yes. MRI scans of other parts of your body are safe after knee replacement. Although some old MRI scanning equipment may not be compatible with your prosthesis, the majority of MRI scanning equipment today is safe and compatible with knee replacement parts. You may also have a CT scan of any part of your body after a knee replacement.

How will I know if my knee implants happen to be recalled?

In the extremely unlikely event of a recalled implant, you will be contacted by the company who made the device. All implants have lot numbers registered with the implant maker. This information is kept in your medical record. If you want a copy of your X-ray or exact implant type and model for your records, please ask your physician.

Rest assured that of the millions of artificial joints implanted each year, the incidence of recall is exceedingly rare. Implant companies monitor the performance of their products very carefully.

Is there a long-term risk of failure of knee implants?

No, the implants are engineered to withstand your body weight and activity level, but the moving parts of a knee replacement do wear over a period of several decades. A properly aligned knee replacement done by a competent, experienced surgeon will usually last the lifetime of most patients.

Subtle component malpositioning and suboptimal orientation can however compromise the lifespan of the implant. This is why the skill and expertise with which the knee is implanted in your body is a critical determinant of how long the knee will last and how well it will perform.

How many times can you replace a total knee?

With modern technology, cases that were considered hopeless a few years ago can undergo successful knee replacement surgery. Such complex knee replacements are done every week in our specialty practice, and are referred from all over. So, there is no hard and fast rule as to how many times a knee can be replaced. Knees that have had multiple operations may be missing structural bone support, muscle cover, and quadriceps support.

While doctors hope that you never need such complicated knee operations, it is possible to get patients mobile again in situations that would have resulted in an amputation in the past. This reflects advances in surgery techniques and related technology.

What if I receive conflicting advice and opinions from other people taking care of me in the hospital or during home health visits?

Your own surgeon is your best resource.

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, surgeons 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 expect surgeons to adopt them only after carefully considering the advantages, safety, and scientific merits of such designs.

What brand of knee implants do you use?

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 as of this writing (2014.) 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.)

Can you show me the parts used in a total knee replacement?

Your surgeon should be able to show you actual parts and will probably have other materials such as animations or video that you can see.

What if I want a different brand of knee prosthesis?

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 this website.

If truly innovative implants are introduced, the odds are that I or some of my colleagues 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 talk to your surgeon.

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 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.

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 that we used incorporate these modern design features.

Other variations in total knee implants include a ceramic “oxinium” surface, the “rotating-platform” knee, and other brands marketed by implant companies. Discuss this with your surgeon and medical team; they will help you make an informed choice.

Can I get a “golfer’s knee” implant?

As above, if you prefer one kind of implant over the other, ask your surgeon. 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 most exciting innovations when I was practicing 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.

We used this in my practice beginning in 2013 and found it truly innovative, a meaningful step forward in knee replacement surgery. Our results showed 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 serveds as consultant surgeon for CONFORMIS, and was on a surgeon advisory and design team for this company. He did not receive any royalty or other payment to promote or implant CONFORMIS knee products, however, since the consulting activities concern other CONFORMIS technology platforms.)

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, cadaver tissue can be used 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, 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.

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, there are 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.

Life with an Artificial Knee