Dr. Herbert D. Huddleston Presents:
Arthritis of the Knee Joint
TOTAL KNEE REPLACEMENT SURGERY
The modern total hip replacement was invented in 1962 by Sir John Charnley, an orthopedic surgeon working in a small country hospital in England. His work has been one of the great triumphs of Twentieth Century surgery. Two revolutionary features of the Charnley hip replacement were 1) the combination of metal gliding on plastic, and 2) the use of methacrylate cement to attach the artificial components to the bone. A Canadian orthopedic surgeon (Gunston) working with John Charnley applied the principles of hip replacement to the knee. His knee replacement was received with some enthusiasm by many surgeons. Other surgeons quickly began to work on newer designs for an improved knee replacement.
The operation has become fairly routine and is successful around 96% of the time. One of the first American surgeons to perform this type of knee surgery was Charles O. Bechtol. He started a total hip replacement program in 1969 while he was professor of orthopedic surgery at UCLA. He also designed a knee replacement system which was widely used and accepted in the U.S. Dr. Huddleston studied hip and knee surgery with him for one year in 1975. The two later became partners in a private practice restricted to total joint replacement. Dr. Bechtol retired in 1984 and Dr. Huddleston took over the practice and merged the practice with the Southern California Orthopedic Institute in 1988. The knee replacement designs which were available during the early 70’s were decidedly inferior when compared to the hip replacement devices available at that time. However, by the late 70’s, the surgical technique improved considerably and better designs became available. A major improvement was the development of accurate instrumentation for installing the new knee surfaces. Today knee replacement surgery is at least as good as hip replacement surgery. The major problem with hip replacement surgery is durability. This is also a problem with knee replacements but a good knee replacement is probably a more durable operation than a good hip replacement. The operation of knee replacement is much more complicated than hip replacement to perform.
The term “knee replacement” sounds like a more radical procedure than it actually is. Most patients imagine that 3 inches of bone is removed from each of the knee bones and that a large metal and plastic device is installed in its place. In actual fact, the procedure is more akin to dentistry and a better term would be Knee Resurfacing. A thin layer of bone is removed from the damaged surface of the femur (thigh bone) using special instruments which remove the correct thickness of bone. The removed bone is then replaced by a thin layer of metal, approximately the same thickness as the bone which was removed. In a similar fashion the upper end of the tibia (shin bone) is removed and is replaced with a wafer of plastic. The back part of the knee cap (patella) may also be resurfaced with a piece of plastic.
The three parts are attached to the bone by means of a “bone cement” (methylmethacrylate). When this cement is first mixed it develops a dough-like consistency. This dough is pressed into the bone and the parts of the Prosthesis are pressed into the dough. The cement then hardens over 10 to 15 minutes into a plastic-like consistency. After the knee has been replaced, the metal “cap” covering the end of the femur rubs against the plastic covering on the end of the tibia, preventing bone from rubbing on bone and giving relief from pain. The plastic is high density polyethylene a material which has a very low wear-rate and a very low frictional resistance when rubbing against the highly polished metal surface.
NEWER DEVELOPMENTS IN KNEE REPLACEMENT
As with hip replacements, a major long-term problem with knee replacement is loosening. The bond of the cement to the bone can come loose. This looseness and micro-motion can result in pain. It can also cause a loss of bone. If the pain or bone loss from loosening gets severe, a second surgery is sometimes necessary. Because of this loosening problem, surgeons and bioengineers constantly strive to develop new techniques and designs to improve the fixation. The newest concept is to do the operation without cement. The prosthesis has a rough surface into which the bone can grow. It is hoped that this bond will be more durable than cement fixation.This type of operation is called a “cementless total knee replacement” (also referred to as a porous in-growth knee replacement”). There is a great deal of enthusiasm for cementless hip replacements which have been available since 1978. They have worked very well in the relatively short-time that they have been used. Cementless total knee replacements have been used since 1982. They have not been as successful as cementless hips. The bone does not always bond successfully to the implant. The long-term place of cementless knees replacements has not been worked out yet. There are many types of these devices available today. Young people who particularly need increased durability with a knee replacement are more likely to be good candidates for a cementless knee replacement. In addition to this it has been found that the part of the knee replacement which attaches to the femur more readily bonds to the bone without cement than do the parts on the tibia and patella. For this reason, many surgeons use a cementless component on the femur but continue to cement the tibial and patellar components. This mixture of cemented and uncemented parts is known as a “hybrid" (mixed) total knee replacement.
The choice between cementing all the components, none of the components, or doing a hybrid knee is made at surgery and depends mainly on the quality of the bone. Dr. Huddleston cements all the knee components in most cases in patients over fifty.
OTHER SURGICAL CONSIDERATIONS DURING KNEE REPLACEMENT
- If your leg has a fairly normal alignment to begin with, you can expect that it will be "straight" after the operation. However, if your legs are severely bowed or "knock-kneed" there is a good chance that the alignment will not be "normal" after the operation.
- Your patellar tendon may require detachment from the shin bone during the operation if you have a "tight" knee with a lot of scar tissue. If so, you may have to wear a splint or cast on the leg for several weeks after the operation, but this is not common.
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Implant Designs and Materials
Arthritis of the Knee Joint copyright © 1999 Herbert D. Huddleston, M.D.