conformis

What goes on during a knee surgery?

Here are typical procedures that may help you understand the procedure.

How do you attach the artificial knee to my bone?

Your orthopedic surgeon will probably use bone cement to do this. The majority of total knees are affixed with cement, although un-cemented designs are also used. Outcomes from both are very good. For young and active patients, cement-less total knees are usually preferred because of excellent fixation and durability. Living bone next to the prosthesis keeps the implants secured over time, whether or not cement is used. The choice of cemented versus un-cemented knee depends on many factors, such as patient age, knee deformity, status of ligaments, and the quality of bone.

Who does the actual surgery?

Although team members will assist, and resident physician or students may observe, you should expect that a competent orthopaedic surgeon will perform the entire operation.

Does the orthopedic surgeon replace my kneecap too?

In part, yes. On the underside your own kneecap (also called the patella) a thin layer of arthritic cartilage and bone is removed during surgery. In its place, surgeons affix a plastic kneecap to your own remaining kneecap. This new part functions just like your own kneecap. The front surface of the kneecap is your own bone; it is the underside of the kneecap that is lined with plastic.

Are knee ligaments removed during surgery?

Internal knee ligaments (anterior cruciate ligament and posterior cruciate ligament) are usually so worn out in arthritic knees that what remains of them is removed. The knee prosthesis itself is engineered to substitute for internal knee ligaments and stabilize the joint.

New knee designs, such as the CONFORMIS custom-knee that is built for each patient offer the benefit of preserving knee ligaments. New knee designs and materials are constantly being introduced.

The supporting ligaments outside the knee joint are usually preserved during replacement surgery. These external ligaments are called the medial collateral ligament (located to the inside the knee) and the lateral collateral ligament (located to the outside of the knee). These ligaments continue to function after knee replacement surgery. For severe deformity, arthritic destruction, or unusual cases, prosthetic designs can substitute for all knee ligaments, providing more stability when compared to routine total knee prosthesis.

Thus, even very unstable and deformed knee joints can be replaced successfully, allowing the patient to fully weight-bear immediately, without fear of the knee giving out, and without knee braces. The choice of implant is based on the individual case and amount of knee joint deformity, as well as surgical judgment.

Will my leg have a tourniquet on during surgery?

A thigh tourniquet is a device like a blood pressure cuff. It is placed on your thigh and inflated to let the surgeon operate more easily by cutting off the blood supply to the leg while the knee joint is open.

For convenience and out of habit, many surgeons in the United States do use a tourniquet for knee replacement surgery. It is worth asking him or her about. Tourniquets can lead to increased tissue trauma to the thigh muscles, which are squeezed hard for the entire duration of surgery, and a lack of oxygen to the entire leg during the operation. The result is pain, tissue damage, and delayed recovery.

Will the knee bleed more without a tourniquet?

Studies have shown no difference in blood loss during knee surgery done with or without a thigh tourniquet. Without a tourniquet, most blood loss occurs during the operation. If need be, this blood can be collected by a cell-saver device and given back to the patient. With a tourniquet squeezing the thigh, all the blood loss occurs after the tourniquet is let down and oxygen-deprived tissues get the blood flow restored. This blood is usually collected in a drain placed in the knee joint after surgery and discarded.

How does computer navigation help in knee replacement surgery?

Precise alignment of the bones during knee replacement is critical to the long-term performance of the joint replacement. Computer programs can help in such alignment of bones, and reduce the possibility of error. Beyond computer-assisted technology, robotic arms help position bone preparation guides very precisely, and optimize the result for each patient.

With the advent of the custom-made knee replacement by CONFORMIS (Boston, MA), the need for gender-specific knees, left versus right knees, race-specific knees, high-flex knees, computer navigation, robotic-assisted surgery, and other supportive technologies is entirely obsolete and a thing of the past. With a custom-designed knee replacement, the fit, fill, sizing, orientation, rotation, depth, shape, contours, geometry, flexibility, and instrumentation are all optimized for one particular knee, unique to the individual patient. These parameters are optimized to their theoretical extreme, such that surgeon-to-surgeon variability is minimized, thereby maximizing patient outcomes, recovery, safety, reliability, and quality. This technology is revolutionary and commonly used for total knee replacements. Added benefits are simplification of surgery, reduction in product inventory and complexity, and the reduced chance of error.

In the world of knee (and hip) replacement surgery of tomorrow, custom-built implants will increasingly become adopted as surgeons and hospitals see the efficiency and benefits of this technology, at no added cost, and little downside. That is why we preferred to build each knee implant on a custom basis, for each patient. No two people are alike, and that applies to the knee joints as well, providing the most compelling, logical, and reasonable rationale for a custom, patient-specific approach to knee replacement.

Ask your surgeon about the latest materials and procedures.

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.