Total Knee Replacement Overview
By Dr. Lancaster
Total Knee Replacement in the New Millennium
Orthopaedic surgical techniques and technology, like all aspects of science and technology, have continued to undergo advancements and improvements over the years. Total knee replacement or total knee arthroplasty, (TKA), specifically has continued to improve with time. There are currently over 225,000 total knee replacements performed in the United States of America each year. Total knee replacement is one of the most successful procedures in orthopaedics. Medicine in general due to the high success rate and high patient satisfaction rate. Total knee replacement can improve function, motion and decrease pain such that the individual can continue to function actively in their later years. It maintains and improves an exercise tolerance which enables them to remain active and improves their overall life style.
Frequently, patients with degenerative joint disease or arthritis will be forced to reduce their activity due to pain. Therefore, this may result in progressive weight gain and subsequent depression from the inability to perform their normal daily activities. When the deterioration of the joint surfaces is significant enough and all nonoperative treatments have failed, a total knee replacement is the choice. In the later years of the “past millennium” or reasonably the 1970s and 1980s, a total knee replacement was commonly thought to last five years.
In reality they were not far off. In the early years this was due to mechanical loosening of the cement (or grout) and prosthesis (or metal implant). With improved metallurgy, biophysics and better techniques, the 1990s have improvements in technology and the track record became better. With the improvements in technology, the “weak link” has increasingly become the plastics. As the longevity of the knee implant improves, we have found that the plastics or polyethylene has elevations in wear rates over the years and the debris has led to some cases of loosening.
Improvements in Implants for Knee Replacements
The improved implants are minimizing this problem. The other drawback in total knee replacements has been the lack of complete improvement in motion of the knee. A total knee replacement will reproducibly and consistently improve pain and function about the knee. However, this will not always significantly improve motion about the knee. Most arthritics have already a significant stiffness about the knee by the time they come to surgery. This is due to their levels of pain and as a result of the natural progression of their disease. A total knee replacement will improve this motion but not fully return it to the “normal” range of motion.
Newer concepts in total knee replacement show improvements in both the wear rates or destruction of the plastics. They also have improvements in the motion of the knee. Normal knees move not only in a forward-backward plane termed flexion and extension, but also will rotate to some degree with such activities as swinging a golf club, swinging a racquet or pivoting as with exercises. The knees of the “last millennium” for the most part are only for the forward-backward motion. A revival of an old concept, coupled with improved kinematics (motion studies) and improved plastics has produced the “mobile bearing” knee of the new millennium.
Improvements in Range of Motion
It allows motion both in the flexion-extension (or forward-backward) plane and also allows movement in rotation. As such, it improves overall motion and function. The mobile bearing knee coupled with the new ideas and studies on the sacrifice of the posterior cruciate ligament has led to results of improved function and motion of the knee, replicating close or equal to the normal knee motion.
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