Prosthetic joint replacement 
for knee arthritis is an increasingly common procedure in the US. The indications are severe osteo-arthritis of the knee and pain that is not relieved by conservative measures including oral medications, physical therapy, and injections. The clinical picture is one of 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, most commonly 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. The only good long term solution is to replace the cartilage with a metal plastic prosthesis.
Although many patients present with
various sophisticated imaging studies such as MRI and CT scans, the best imaging study to assess osteoarthritis is a plain x-ray. A standing x-ray allows visualization of extent of the cartilage loss because the bones will often make contact when weight bearing. When the cartilage loss involves all aspects of the knee joint (tri-compartmental osteoarthritis ), total knee replacement generally recommended.
ALTERNATIVES TO KNEE REPLACEMENT SURGERY
Many patients request alternatives to surgery for the treatment
of their arthritis. Specifically, polymer injections or arthroscopic surgery are often mentioned. There are a number of polymer injections 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. 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 is roughly $500 for a series of 3-5 injections. The polymer is injected on a weekly basis for 3-5 weeks. 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, you will receive a prescription and have it filled at a pharmacy. You will then return on a weekly basis to have the medication injected
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. We do not recommend arthroscopic debridement for the treatment of knee osteoarthritis as the risks of the surgery outweigh the transient benefits.
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 concomitant 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 often an issue. They are a reasonable alternative to joint replacement.
There are several different total knee replacement implants available on the market and many manufacturers have started using direct to consumer advertising. Most prostheses have the same basic components: a polished metal femur, a metal tibial component, a plastic patella component, and a plastic tibial tray
The surgery is
done under a tourniquet to decrease the amount of bleeding during surgery. Most joint replacements can be performed 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 receive 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, pain control after surgery is much better than with single agents alone.
After surgery, patients start on a medication called Lovenox which is a low molecular weight heparin used to minimize the risk of developing DVTs (blood clots) in the leg. Without this medication, the risk of developing a deep venous thrombosis or DVT is about 50%. This complication can be fatal if the blood clot dislodges and travels to the heart. This condition is called pulmonary embolism. The risk of developing a PE or pulmonary embolism is about 0.2% with Lovenox.
Patients stand the night of surgery and physical therapy starts more aggressively on the first day after surgery. Patients 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. Patients may shower after the 5th day and should 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.
Most patients are understandably anxious about having surgery to replace the knee joint. 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 around the first 6 weeks. After about 6 weeks, the pain from surgery decreases dramatically and knee function 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. You should consider the long term outcome of the surgery as your 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. If you insist on having a small incision with MIS technique to replace your total knee, then you we will recommend that you see another surgeon. 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 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 implant 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. We do not offer total or partial knee arthroplasty in patients 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 is 2-3 times higher in morbidly obese patients. We recommend patients seek help to get their BMI down to a safe level before proceeding with a total or partial knee replacement under less than ideal circumstances. The article below is helpful in understanding the scientific basis for this decision.
Patients come in about once a year for x-rays of their knee to make sure the polyethylene insert is not wearing out. This is detectable early by looking at the x-rays over time. When the plastic insert becomes less than 5 mm thick, revising the knee by replacing the polyethylene insert is advised. If done early, we can replace the plastic insert without having to change out the rest of the knee replacement. If patients wait too long, the particles from the worn out plastic can cause loosening of the remaining implants (reactive osteolysis) and this necessitates revision of all components of the total knee. This is a much larger surgery with longer recovery time.
The post-op total knee instruction sheet 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.
