X-rays before and after knee replacement
Total Knee Replacement
Prosthetic joint replacement for knee arthritis is an increasingly common procedure in the US. The indications (reasons for doing the surgery) are severe osteo-arthritis of the knee and pain that is not relieved by conservative measures including oral medications and injections. The clinical picture is loss of cartilage in the joint causing pain, limitation of motion and impairment of activity. Most patients with severe arthritis have progressively incapacitating knee pain, limping and restricted range of motion. In addition, many patients notice an increasing deformity in their knee and the most common is a "bow legged" alignment. This change in alignment is caused by the loss of the gliding cartilage that covers the ends of the bone. Once this cartilage is worn down, the underlying bone is exposed and the bone surfaces on either side of the joint rub against one another. This produces a creaking sensation and a very strong inflammatory reaction with swelling, increased joint fluid, stiffness and pain. Once the cartilage has worn off the end of the bone, it cannot be replaced with new cartilage and invariably the only good long term solution is to replace the cartilage with a metal plastic prosthesis.
Although many patients present to my office with various sophisticated imaging studies such as MRI and CT scans, the best imaging study for the assesment of osteoarthritis is a plain x-ray. I routinely obtain standing views of the knee in which the patient stands of the involved leg when taking an x-ray. This allows me to see the extent of the cartilage loss and the bones will often make contact when the patient is standing. In cases where the cartilage loss is diffuse and all aspects of the knee joint are involved this is referred to as "tri-compartmental osteoarthritis" and in these cases I recommend a total knee replacement.
AP and Lateral x-rays showing end stage, tricompartmental osteoarthritis
ALTERNATIVES TO KNEE REPLACEMENT SURGERY
Many patients will request alternatives to surgery for the treatment of their arthritis and will specifically request polymer injections or arthroscopic surgery in lieu of a major joint replacement. There are a number of polymer injections that can be administered that give good pain relief for up to 12 months with a series of 3 injections. The polymer coats the exposed bone in the knee joint and reduces inflammation and pain. I have included links to the two most poplular injectables below. They are useful in moderate osteoarthritis and can be used to delay surgery for a year or two. Unfortunately, many insurance companies will not pay for the cost of the injectable which costs roughly $500 for a series of 3-5 injections. The polymer is injected on a weekly basis for 3-5 weeks and can give up to 12 months of pain relief. The risks of the treatment are infrequent with about 1 in 100 patients developing a reaction to the polymer and this can actually worsen symptoms. There is a small risk of infection with repeated injections of roughly 1 per 300 patients. For patients who wish to try the polymer injections, I give them a perscription and have them fill the medication at a pharmacy and they return on a weekly basis to have the medication injected
Supartz
Synvisc
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Arthroscopic debridement of osteoarthritis has not been shown to be of any benefit in the long term as it does not arrest the disease process. During arthroscopy, a large amount of fluid is flushed through the knee joint and this helps to reduce the inflammation in the joint, but the relief is transient. I do not recommend arthroscopic debridment for the treatment of knee osteoarthritis as the risks of the surgery outwiegh the benefits which are transient.
Knee Arthroscopy
Bracing has been advocated for patients with unicompartmental osteoarthritis. The most common clinical presentation is patients with genu varum or bowed legs and pain on the inner aspect of the knee joint. X-rays typically show loss of articular cartilage on the inner aspect of the knee but preserved cartilage under the knee cap and on the outer portion of the knee. In these instances braces that "unload" the cartilage on the inner aspect of the knee can help and may delay the need for surgery by 2-5 years. The braces tend to be uncomfortable so compliance is a bit of an issue, but they are a reasonable alternative to joint replacement. I have included a link for the knee unloader brace below
Knee Unloader Brace Info
Examples of knee unloader braces
There are several different implants available on the market and many manufacturers have started using direct to consumer (DTC) advertising. Most prostheses have the same basic components: a polished metal femur and a plastic tibial tray. I use two different types of prosthesis designs for total knee arthroplasties: fixed tibial bearing and rotating tibial tray. The choice of the prosthesis depends on how difficult I anticipate the soft tissue balancing, especially with regard to the patella (knee cap) and the amount of contracture in the knee before surgery. I have included the links for each type of prosthesis below. The literature has not shown a signficant difference between the two types of prosthesis with regard to functional outcome or wear rates. I use the rotating platform prosthesis in cases where I anticipate problems with soft tissue balancing such as in knees with a severe pre-operative deformity or contracture.
Stryker Triathalon TKA
DePuy RP TKA
The surgery takes approximately two hours and is done under a tourniquet to decrease the amount of bleeding during surgery. I do most of the joint replacements under a regional anesthetic such as a spinal because the pain control after surgery is much easier with a regional anesthetic and the amount of bleeding is reduced. In addition, many patients recieve a femoral nerve block which gives an additional 24-36 hours of pain relief without affecting rehabilitation with physical therapy. When combined with oral pain medications such as oxycontin and celebrex, control of pain after surgery is much better than with single agents alone.
After surgery all patients are started on a medication called low molecular weight heparin to prevent blood clots in the veins of the pelvis and leg, which is the single most common complication after surgery. The medication that I use currently is called Lovenox and I have included a link below:
Lovenox
I have patients stand the night of surgery and then physical therapy starts more aggressively on the first day after surgery. I routinely use a CPM (continuous passive motion) machine after surgery. Most patients are comfortable and go home with a walker on the 3rd day after surgery. I allow my patients to shower after the 5th day and encourage them to walk as much as possible after they return home. Most patients are able to walk comfortably with a cane after about 2 weeks and without a cane after 6 weeks.
Basic Components of the Total Knee Implant
CPM Machine in use after knee replacement
Most patients are anxious about having surgery to replace the knee joint which is understandable. I tell my patients to expect to be discouraged in the first 3-4 weeks after surgery because the progress with rehabilitation is slow in the first month and your knee stays swollen and stiff for the first 6 weeks or so. After about 6 weeks, the pain from surgery decreases dramatically and your knee function really starts to improve. By 3 months, most patients are very happy with the outcome of the surgery and walk without a limp or assistive device.
There is some debate in the literature about using a"minimally invasive surgical" (MIS) approach to perform a total knee arthroplasty. The advantage of doing a smaller surgical incision is less pain, swelling, bleeding and faster rehabilitation after surgery. For most patients this is their primary focus. I caution patients to consider the long term outcome of the surgery as their primary focus. There are several studies in the literature which suggest little short term benefit from doing a minimally invasive technique and long term detriment from implant malposition using an MIS technique. The single most important factor in achieving a good outcome from total knee arthroplasty is accurate placement of the prosthetic components to achieve good soft tissue balancing. This requires a fairly large incision to accomplish and the drawback of a minimally invasive approach is that it is more difficult to ensure the components are placed correctly. So even though your hospital stay may be shortened by a day or two with an MIS approach the long term problems associated with component malposition make this technique less and less attractive. I caution my patients to be aware of the potential complications and I use a surgical approach that ensures that I can place the components properly. If you insist on having a small incision with MIS technique to place your total knee then I would probably recommend that you see another surgeon because my philosophy is to make sure the total knee is placed correctly and I do not focus on the length of the incision. Below are links to abstracts or manuscripts in recent peer reviewed publications about the outcomes of MIS total knee replacements
MIS abstract, CORR 2010
MIS abstract JBJS 2010
MIS meta-analysis 2010, J Arthroplasty
MIS TKA full text, JBJS Jul 2010
Most total knee implants are designed to last somewhere between 15-25 years. The factors that influence the rate of wear of the polyethylene liner (the plastic portion of the total knee that wears out over time) include activity level (running and impact activities are discouraged as they increase wear), weight (obesity is one of the primary risk factors for total knee arthroplasty mechanical failure) and manufacturing characteristics of the polyethylene. I do not offer total knee arthroplasty in pateints with a BMI (Body Mass Index) of greater than 40 ( this is the objective definition of morbidly obese). The reasoning is that the relative risk of complications including infection, wound problems, soft tissue balancing problems, patellar tracking problems and component malpositioning are 2-3 times higher in morbidly obese patients. I would recommend patients seek help to get their BMI down to a safe level before proceeding with a total knee replacement under less than ideal circumstances. I would suggest the article link below helpful in understanding the scientific basis for my decision.
Obesity and total knee Arthroplasty, JBJS, 2004
The current polyethylene manufacture uses and oxygen free environment and forms highly cross linked polyethylene which is able to resist shear wear better than non-cross linked plastic. As a rule, I have my patients come in about once year for x-rays of their knee. I check to make sure the polyethylene insert is not wearing out and I can detect this early by looking at the x-rays over time. When the plastic insert becomes less than 5 mm thick, I recommend revising the knee by replacing the polyethylene insert. If done early, I can replace the plastic insert without having to change out the rest of the knee replacement which means much less surgery for my patients. If you wait too long, the particles from the worn out plastic can cause loosening of the remaining implants and this necessitates revision of all components of the total knee. This is a much larger surgery with longer recovery time. The link below describes the annealing process for highly crosslinked polyethylene and the benefits of this processing over standard polyethylene
X3 cross linked Polyethylene pdf
I have included a link to my post-op total knee instruction sheet which covers a number of questions about what to expect in the hospital, what types of exercises to do, how long you will be in the hospital and what to expect after surgery. This should answer most of the questions you will have.
Total Knee Post Op Instructions