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Total Knee Replacement

Total Knee Replacement :: Unicompartmental Knee Replacement :: Patellofemoral Replacement

Mckeever Knee

Picture #1 is the original "unispacer" designed by Dr. Duncan McKeever of Houston, Texas. Dr. McKeever abandoned this design as the results of total knee replacement were superior.

Knee replacement may be total or partial. As discussed before, sometimes only the patellofemoral joint is replaced. In some instances, either the inside half or the outside half of the knee is replaced. In Houston in the 1960s, Dr. Duncan McKeever developed a type of replacement in which half of the knee was replaced. This was a metal wedge that was placed into the worn side of the joint.

This device was helpful for patients, but as total knee replacements improved and those results in patient satisfaction with total knee proved to be superior to the partial knee replacement, this knee replacement fell out of favor. In the early 2000s, the Sulzer Corporation released and aggressively marketed a device known as the "unispacer" (see image at right) which was based off of Dr. McKeever's and other designs of the '60s.

Unispacer Knee

Picture #2 is the "modern unispacer" produced by the Sulzer Corporation recently with results no better than those of Dr. McKeever. "Those who cannot remember history are condemned to repeat it" - George Santayana (1863-1952).

Unfortunately, because Dr. McKeever had FDA approval for his device, and because the FDA allows for new products which are similar to old products be introduced without further FDA testing, this unispacer was released to the market without additional clinical studies. Subsequently, clinical studies using this device have shown that its use is ill-advised. Although there are rare reports of success, infections and other failures have led most joint replacement specialists (Dr. Clyburn included) to recommend against this procedure.

Knee Replacement
This set of pictures are of a truly modern unicompartmental knee replacement patient. The first is an x-ray showing loss of joint space on the inside (medial) joint space. The second is an intra-operative picture of the unicompartmental knee replacement in the knee. The third is an x-ray of the unicompartmental knee replacement in the knee.
Knee Replacement

There is much written and advertised about the total knee replacement. Minimally invasive surgery (MIS) has become widely popular. Patient satisfaction rates are very high, with well over 90 percent of patients being totally satisfied. Over the past 50 years of use of total knees, the life expectancy or time that they are expected to last, has improved dramatically. Approximately 86 percent of total knees are still working well at 15 years follow-up.

There are many different designs of total knees. They can be classified into those that keep the posterior cruciate ligament and those that do not (posterior cruciate sparing and posterior cruciate sacrificing). The posterior cruciate ligament is often diseased in the arthritic knee. It may be very tight or even ossified, meaning that it has turned into bone. In Dr. Clyburn's opinion, most knees should be replaced with a posterior cruciate sacrificing design, and the sparing design used only in cases where the arthritic process is fairly mild. In Dr. Clyburn's practice, he usually chooses the posterior stabilized design. He also has, on many occasions, seen patients with a cruciate sparing design who either have stiffness or instability. These patients often improve dramatically when they are revised to a posterior stabilized design.

Total knee replacement can also be classified as either fixed bearing or mobile bearing. In the fixed bearing design, the polyethylene part is fixed to the metal plate of the tibial component. All of the movement of the knee occurs between the femoral component and the polyethylene. In the mobile bearing design knee, there is movement allowed between the polyethylene and the metallic tibial component, allowing this design to attempt to move in a more anatomically correct fashion. However, long-term studies of both the fixed and mobile bearings show similar results.

Advertising of Specific Total Knees

Gender Anterior FlangeThere is much marketing today with regard to specific total knee designs. One advertiser states that their knee is the only one designed to bend and rotate. Remember that this marketing is written by advertising executives working for the manufacturer. In fact, all knees are designed to bend and to rotate. Total knee replacement would not be successful today had they not been designed from the beginning to bend and rotate.

Another manufacturer, Zimmer, which is an excellent company, is aggressively marketing their gender specific knee. This design focuses on two general principles. One is that women's knees tend to vary more in size in the front to back (AP) and side to side (ML) proportions than men. They, therefore, changed the sizing slightly and added 1/2 sizes (like shoes). Also, because women tend to have more "knock-kneed" than "bowed" legs, their patellae (knee cap) function slightly differently than those of men. They, therefore, slightly changed the way the patellofemoral parts function. Other manufacturers have made similar modifications but did not market them as specifically for women. In some ways, it is similar to the tobacco industry which marketed cigarettes specifically for women, even though, for the most part, it was simply a cigarette. This type of design holds promise and deserves attention and study; however, there are currently no long-term or even mid-term studies showing superior outcomes of these implants.

Computers and "Navigation in Total Knee Replacement"

Dr Clyburn has been in the forefront in the use of computers and navigation in total knee replacement. We have performed a research study and clinical study of navigation.

Total knee Replacement - Computer screen Total knee Replacement - Computer screen

We have not found this technology to offer an improved outcome and thus we do not use it routinely. However, we do continue to study this technology.

Knee Replacement For much more information about Knee Replacement

 

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