Knee Replacement Surgery

Is this a minimally invasive surgery?

Full knee replacements (total knee arthoplasty) require precision and accuracy to ensure proper functioning and longevity. Our surgical approach depends on many factors including patient size or possible pre-existing conditions such as severe deformity or stiffness. In addition, patients with inflammatory conditions (ie. Rheumatoid arthritis) may require a more extensive exposure for removal of inflamed tissue (synovium).

We use a variety of surgical approaches around the knee. Less invasive approaches include the quadricep-sparing and sub-vastus approach. These are performed when patient factors will allow. They are less invasive in that we do not cut high into the quadriceps muscle and tendon region which often results in less pain, faster recovery and improved early range of motion after knee surgery. In general, knees hurt more than our AMIS hips for a number of reasons. Even in the less invasive approaches, the knee will often fill up with blood after the surgery. This is in part because of the blood thinners we start you on the day after surgery. Like hip replacement, knee replacements are high risk for DVT (deep vein thrombosis) and PE (pulmonary embolism) which are clots in your legs and/or lungs. The blood thinners help reduce the risk of developing these clots, however, they often cause some bleeding, bruising and unsightly wounds on occasion. The knee is also a fairly superficial structure unlike the hip which is buried deep under layers of muscle. When the knee fills up with blood after surgery it can be quite sore and patients become reluctant to move their knee. They often describe it as though there was an “elastic band” around their knee. Range of motion exercises, ice and a good physical therapy program will help you get your motion back and improve function after your knee replacement. The bottom line with the approach is that we will use the smallest, least invasive approach available without compromising proper sizing, alignment and placement of your new knee. We use many adjunctive pain measures including local anesthetic injection, spinals and nerve blocks which we will discuss later.

What is new in Knee Replacement Surgery?

Modern implants are more durable. Extensive research and improvements in manufacturing have resulted in total knees that have much improved wear characteristics over their predecessors. One of the rate limiting steps in joint replacement is the plastic bearing that is sandwiched between the two metal pieces attached to you thigh bone and shin bone. This plastic liner (polyethylene) forms the artificial cartilage surface for your new knee replacement. Over many years, this artificial bearing surface is subject to significant loads and stress during normal human activities. This starts a wear process where small microscopic plastic wear particles are released into the joint fluid bathing your new knee replacement. When enough of these particles accumulate, they will trigger a process called “osteolysis” (“bone-melting”). This bone melting occurs because your immune cells see the foreign plastic particles as “enemies” and start an inflammatory process that will often result in the slow destruction (melting) of bone around the knee joint. When this happens, the knee starts to hurt and the parts fixed to the bone will often loosen requiring revision (re-do) surgery. Plastics are now designed with special cross-linking and more durable characteristics that should resist wear and last longer, however, they will all wear out given sufficient time, load and stress.

Putting the knee in properly is probably even more important than new plastics. We know based on the data and studies in the literature, that knees that are put in crooked don’t last very long. The analogy here is like putting new tires on your car. We can put the best tires in the world on your car, however, if they are not properly aligned and balanced they will wear out quickly. As surgeons, we strive to put the knee in perfect every time.

How do we do this and what has technology done for us as surgeons in this regard?

Conventional total knee replacements have been done for years using alignment rods during the surgery. Surgeons use measuring rods either inside the bone (intra-medullary) or on the surface of the bones (extra-medullary) in the leg to determine the overall alignment. What we have learned is that even in the most experienced hands (ie. Specialists who do more than 100 knees per year), this conventional measuring system is not extremely accurate. In fact, the data suggests that we get it wrong about 20% of the time. Now hold on; this doesn’t mean that we are putting your knee in backwards!! It means that when we critically evaluate the “alignment” of the leg we are at least 3 degrees away from perfect. Now three degrees doesn’t sound like much but studies show that replaced knees with more than three degrees of error don’t last as long and have a higher risk of failure. So how do we make ourselves more accurate? Computer navigation is something we started doing years ago to improve our accuracy in knee replacement surgery. We helped develop the system and even coupled it to a robot. We found that it increased our accuracy tremendously (99.6% were perfect), however, it required extra time in the operating room and required that we drill pins into your leg to measure and record what we were doing during your knee surgery. We decided we needed to develop a faster, less invasive way of improving our accuracy. In conjunction with a Swiss based company (Medacta) and a couple of other surgeons, we designed the MyKnee system for total knee replacement. This system uses “pre-navigated” cutting blocks to make us extremely accurate without subjecting our patients to the pins and longer or times.

A CT scan is performed from your hip down to your ankle with high resolution 3-D images of your knee. We then use computer technology and virtual 3-D imaging to place your knee in the perfect position in this virtual reality space. The surgeon can make anatomical adjustments to adjust for each and every unique aspect of an individual patient. Once we find the “sweet spot” for the knee, the engineers create a high density plastic bone model of your knee and specific cutting blocks/guides that allow us to precisely place you new knee. This adds incredible accuracy and efficiency to the procedure. The many advantages include: improved knee placement, improved knee function, less invasive, shorter anesthetic time and incredible accuracy without the burden of intra-operative computer navigation (ie. Drilling pins into your bones).

What type of anesthesia?

Our anesthesiologists are board certified and employ modern techniques to make this a very tolerable procedure. These adjunctive techniques will be discussed with you in detail by the anesthesiologist and they will ultimately determine the safest way to proceed. Many of our patients have a combination of general anesthesia with a duramorph spinal and some type of peripheral nerve block. The duramorph spinal is a single, small injection done in the small of your back that contains a longer acting type of morphine. It is very effective at reducing pain for the first 12-36 hours after surgery. Sometimes, this medicine will cause some itching and nausea which can easily be treated if you develop some of these unpleasant side effects. The peripheral nerve blocks involve injecting a longer acting “lidocaine” or local anesthetic (ie. Like the dentist) close to the femoral nerve in the groin area. This injection shuts down the nerve which supplies sensation to the front half of the knee which greatly reduces the pain after surgery. Remember, that it also causes the muscles in your thigh (quadriceps) to relax (ie. Temporarily paralyzed) so DO NOT get up and walk without your knee immobilizer on or YOU WILL FALL! The nurses and physical therapists will assess when you block wears off and when it is safe to try walking without your knee brace.

How long is hospital stay?

The length of the hospital stay depends on many factors related to you as a patient. Younger, healthier patients with few medical conditions can theoretically go home the day after surgery. The discharge largely depends on pain control, the type of blocks, pain pumps or catheters that our anesthesiologists use during your stay. The criteria for going home are fairly simple: stable blood work and vital signs with restoration of normal bodily functions and pain that is adequately controlled with oral analgesics.

What is involved in the rehab/recovery?

The primary focus of the rehabilitation period is regaining range of motion, function and strength. Range of motion is initially difficult because often the knee becomes swollen and fills up with blood after the surgery. The pressure of the fluid in the knee joint often restricts motion initially and causes discomfort. We often will put a drain in your knee for the first 24 to 48 hours to decrease some of this fluid build-up. The physical therapists in the hospital will give you some simple home exercises that we encourage you to do on your own for the first couple of weeks after surgery. At your 2 week follow-up visit we refer you to an outpatient physical therapy clinic. They will push you hard focusing on range of motion and improving the knee function. We are moving away from the use of CPM or continuous passive motion machines as the literature seems to indicate that there is very little difference to patients in terms of recovery. The additional expense and inconvenience is probably not justified based on recent data.