Surgical Techniques - Total Knee Replacement
You need help for the knee pain from arthritis that has gotten so bad you can no longer function well or tolerate the pain with even simple daily activities. The assessment of your knee through a physical exam and a review of your X-rays indicates end of the line arthritis. You are no longer getting any relief with the more conservative measures and this has left you wondering about your next step. What can be done now? …..
The answer may well be a total knee replacement or a unicompartmental knee replacement done with the most advanced minimally invasive surgical techniques and rapid rehabilitation program available anywhere in the world. As a recognized leader, teacher and innovator in minimally invasive surgical techniques for total knee replacement arthroplasty surgery, Dr. Robert Zehr of the Zehr Center for Orthopaedics has had the opportunity to refine the various aspects of the surgical experience for his patients both in the operating room and in the care postoperatively.
Total knee replacement surgery is really quite common. In fact, last year it is estimated that some 550,000 Americans underwent this highly successful operation to relieve the pain of an arthritic knee joint. In this procedure the worn articular cartilage is removed from the ends of the femur (thigh bone) and tibia (shin bone) and replaced with a metal cap and plate with a hard plastic bearing between them.
Since the original knee replacements were done in the early 1970’s great improvements have been realized in the surgical technique, the implants and the recovery and rehabilitation. Yet the question for knee surgeons always remains — can it be done better? The answer is unequivocally — YES!
Personalized Knee Replacement with Custom Alignment
One advancements in the field of knee replacement surgery is the customizing of the alignment of the knee implant specifically to the individual patient. It is thought that if the implant can be aligned precisely to the patients own anatomic alignment, the implant may last longer. This technique will be particularly important to younger patients who need a knee replacement to last longer than is required for the more senior age patient commonly in need of this surgery. To be honest, our current techniques for alignment seem satisfactory for the vast majority of joint replacement patients, particularly the patients over age 65 years as implants for the most part have proven to last several decades or more.
To understand why alignment of a knee replacement is important for all knee replacements, you must first know how the knee is designed. The knee is a “hinge joint” formed by the joining of the tibia (shinbone), femur (thighbone) and patella (kneecap). In addition, there are four key ligaments and several tendinous muscle attachments that control the mechanical motion of this joint. The normal knee joint not only flexes and extends, but also rotates slightly as you run, walk, sit, squat or climb stairs, etc.
Over the years the sliding articular cartilage that covers the ends of these bones wears away exposing the underlying bone. Constant weight bearing and motion across this raw bone is very painful and not well tolerated by most of us. A "replacement knee" implant simply caps these worn out surfaces with metal and plastic attempting to re-establish a painless and functional knee joint with natural motion.
To best reproduce this natural motion in a replacement knee, implant designers must often compromise on some of these elements and substitute for others to create an implant that not only moves well but will also stand the test of time and hopefully last your entire remaining life. In general, most knee implant systems allow enough variability in size and shape to match up with most of our knees, but the natural movement of each person’s knee can be quite unique. With these limitations in mind several new technologies are now available and others will soon be available to the average patient who will need their knee replaced.
Customized Total Knee Arthroplasty with MRI
No surprise to you — You are unique! Your knee is unique only to you. Wouldn’t it just be great if somehow a knee replacement could be designed specifically for YOUR knee? — An implant that aligns to the exact angle that YOUR knee was born to follow from your hip to your ankle. — An implant that matches the rotation that YOUR knee tracks along naturally,rather than one that is "slightly off". Guess what — we are there!
A very specific three-dimensional image of YOUR knee can now be created by computer assimilated MRI images of your hip, knee and ankle from which preoperative planning of your knee replacement can be performed long before coming to the operating room. Additionally, a proprietary system that utilizes these MRI images to construct personalized femoral and tibial positioning guides which are then used in the actual surgery. These personalized guides fit over your femur and your tibia and direct the surgeon to make properly aligned bone resections which provide for exact positioning of the implants onto your bone. This precise attention to the positioning of your implants gives you the best match up of the natural flexion and extension as well as the natural rotation of your original knee – thus personalized and customized just for YOU!
You may ask -- "How is this different from systems already being used by surgeons?" Typically, surgeons use routine X-rays images (2-dimensional) to help choose the size of joint replacement components before surgery from a series of templates. Then, during the knee replacement procedure, the surgeon uses an assortment of instruments to verify component sizing and to establish proper positioning and alignment. Traditional total knee replacement uses instruments or long rods temporarily placed inside or adjacent to the outside of the femur and/or tibia to assist with implant alignment. Not only is this system potentially not as accurate, but can lead to complicating medical issues after surgery.
With the MRI guided design of your "personalized positioning guides", a greater level of detail and precision for implant position and alignment is prepared long before the procedure is even started. More importantly this personalized implant positioning helps enhance surgical efficiency and lessens the chance of certain medical complications.
Additionally, you may ask –“Why do we really care about being this precise about the positioning of the components?” As it turns out, the longevity of your implant (how long it will last?) is in large part determined not just by the design of the implant, but also by how it is 3-dimensionally positioned relative to your hip and ankle. When used in conjunction with a standard array of implants, this computer aided design system allows for a more of a custom fit specifically for you, regardless of race, size or especially gender. The scientific data indicates unequivocally that better aligned knee replacements will last longer than those which are implanted with less precise alignment.
As an aside, you may have heard that knees can also be implanted more precisely with the use of computer alignment system used during surgery. This is quite true, but what you probably don’t know is that most of the computer alignment systems require the surgeon to bury large pins screwed into your thigh bone and shin bone that have reflective surfaces on them. These reflective arrays are sensed by a computer as the surgeon moves your leg around. Upon removal the pins leave holes in the bone which can lead to post operative pain, persistent drainage, infection and even fracture of the bone through this hole. Also, in virtually all cases with the intraoperative computer guided systems, there is a significantly longer operative time for you and the surgeon.
Finally, and even more exciting is that just around the corner lies the technology to take these same MRI derived images of your knee and design a knee implant that is wholly and uniquely just for YOUR OWN KNEE! It will be a great breakthrough that will bring customization to a new level of excellence. Imagine—an implant that is designed from scratch only for you. It really can’t get much better than that – other than a cure for arthritis in the first place!
Men's Knees vs Women Knees
When investigating knee replacement surgery a patient must be careful what they read and a word of caution is in order. There are many fine knee implants available to you and your surgeon. Typically your surgeon will choose an implant based on his extensive experience, scientific evidence and past patient outcomes. If there was one design of knee that worked far better in a woman or a man, most certainly all surgeons would use that implant. As it is, no such "Excaliber" implant exists but, there are many implants by several reputable manufacturers that will work very well for you.
Unfortunately, there continues to be heavy marketing by one manufacturer that there is a "Woman's Knee" or a "Gender Specific Knee" that works better for woman. This marketing implies that all of the other knee implants are really men's knees that are being forced to fit a woman's unique anatomy. What you should know is that in this country more than 60% of knee replacements are done in women and to that extent it makes sense for a manufacturer of implants to focus on this part of the market.
The truth is that a woman's knee anatomy IS slightly different from a man's knee, but with the current implant designs virtually every manufacturer makes its implants in multiple sizes. Results supported by the majority of scientific studies indicate that the "unisex" approach of implants work equally well in women as they do in men. It would be worth your time to review one of the award winning studies among many which investigate the misleading claims of superiority of the "gender-specific knee". This study emphatically concludes that... "the data refute the hypothesis of inferior clinical outcome for women following total knee arthroplasty when using standard components" ( http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2565048/ ).
The fact remains that knee replacement surgery is not perfected as yet and the outcome studies indicate a small yet reproducible number of dissatisfied patients --both men and woman--with their outcome. It does not seem to make any difference which implants are used. Surgeons, manufacturers and therapists are all working hard to improve these outcomes even further, but for now total knee replacement surgery remains one of the best options for a patient whose knee has deteriorated to the point they can no longer do the things they enjoy. Fortunately, the vast majority of patients who undergo knee replacement each year --some 550,000-- are extremely pleased with their results and are able to get back the lives that were in slow gear because of their arthritic knee.
Below are pre-op and post-op X-rays of an arthritic knee which underwent a total knee replacement and is doing very well.