Total Knee Replacement
The progression of established osteoarthritis can be slowed considerably with a number of conservative measures, but it cannot be reversed. Ultimately, the knee joint surface in the active individual can be worn down to the point where the bone surfaces are grinding against each other. On x-ray this is seen as the well known”bone-on-bone” appearance. Since the sensitive nerve endings are located on the exposed surface of the bone, the knee is painful, especially with weight bearing. At this point, viscosupplementation and NSAID’s no longer are effective.
Knee Implant
When it gets to the point where your daily activities are limited primarily by your knee pain, or if you are having pain at night that is not relieved with the above described conservative measures, a knee replacement offers an excellent solution. We no longer think of a knee replacement as a last resort and understand that there are many benefits in replacing the knee before activity levels are severely compromised.
There are a number of choices in Knee Replacement techniques available today. These include partial replacement, total replacement, and minimal incision surgery. There have been significant advances in the design, fit, and sizing of the implants; especially for women. There are new more durable knee components available now that have been laboratory tested to times exceeding 30 years. Surgical techniques have advanced and improved the precision of the implant placement and soft tissue balancing. The result is that knee replacements done today should last longer and outperform their predecessors. More surgical techniques are under development utilizing computer directed fitting, computer navigation, and robotics in knee replacement. With so many new ideas and options available, the choices may seem daunting.
It is important to remember that every knee with osteoarthritis is unique. It is important that the surgeon consider all of the factors including the above mentioned risk factors in osteoarthritis to select the appropriate techniques and prosthesis.
Partial Knee Replacement
The knee has three distinct areas where the joint surfaces come together. These are the medial, lateral, and the patella-femoral compartments. In many individuals, the arthritis or joint injury may be restricted to only one compartment. In this circumstance, replacing the damaged compartment and leaving the other surfaces alone can be very successful. The surgery is less invasive, less painful, and the recovery is usually quicker than a total knee replacement. The ACL and PCL can be retained leading to a more natural feeling knee. This is an excellent solution for many people, but is not applicable to everyone with osteoarthritis. The optimal candidate has isolated medial compartment involvement, full range of motion, an intact anterior cruciate ligament and only a mild varus deformity. It is estimated that about 7 out of 100 people with osteoarthritis are satisfactory candidates for partial (uni-compartmental) knee replacement. Although it’s been around for many years, recently there is a lot of enthusiasm for this type of replacement, and therefore a temptation to expand the indications to younger people with generalized osteoarthritis predominantly in one compartment. Pain relief in these individuals is much less predictable and may be short-lived. In this situation progression of arthritis in the remaining compartments may lead to need for a total knee replacement in the future. In partial knee replacements, careful preoperative evaluation and realistic discussion is essential to assure an excellent result over long term.
Total Knee Replacement
The total knee replacement is the most common surgical technique utilized for advanced knee osteoarthritis with over 270,000 performed in the United States every year. Over the last forty years, since John Insall developed the design and instrumentation for the total condylar knee replacement, tremendous improvements have been made. The new components fit much better, move more naturally through a fuller range of motion, have much better longevity, and allow much greater function. Recent advances in the composition of the metals and the plastics show promise for even greater durability and less wear. Because of this, there has been a trend to proceed with knee replacement in younger patients with severe arthritis before they develop contracture, deformities and significant atrophy.
In a total knee replacement all of the knee joint compartments are resurfaced. The tibia is resurfaced with a titanium base plate and stem. An ultra high molecular weight polyethylene (plastic) surface is placed on top of the titanium to be the actual new joint surface. Titanium is the best choice due to many factors, but one of the major advantages is its compatibility with bone. The titanium and bone have similar flexibility and elasticity. Because of this there is less chance of loosening over time.
The plastic used for the joint surface has undergone some significant changes in the last few years. By treating the components with radiation under certain conditions the plastic becomes cross-linked and more wear resistant.
The most significant development recently is the change in the femoral component. The first choice for the femoral component material, used since the inception of the modern nonconstrained knee replacement is a cobalt chrome alloy. This very strong, wear resistant, and polished metal has done very well over the years providing low friction and slow wearing for its own surface and for the plastic surface. But even with these benefits, the plastic component in active individuals would fail after many years with deformation or cracking due to friction of the metal on the plastic. Several years ago a new material called oxinium was developed primarily to be used in patients allergic to metals, as it is nickel free. Oxinium had excellent material properties for strength and low friction and was a good substitute for the cobalt chrome alloy. In fact over the years in laboratory testing it has been shown to be more durable when combined with the cross-linked polyethylene than its predecessor. The total knee replacement with this combination of materials is called the Verilast Knee. I believe that this is the best current choice for the younger more active individual choosing a total knee replacement.
Minimum Incision Surgery (MIS)
Over the last several years a number of approaches have been introduced in order to reduce the size of the operation and thus the morbidity associated with knee replacement surgery. Modifications in the surgical instruments have allowed the replacement to be done with less incision and less surgical dissection. This should translate into less pain, faster progress, and better outcomes. It certainly results in a smaller incision, but the overall results with the smaller incisions have been mixed. This may be due to the limitation of visibility of some parts of the knee due to the limited incision. I believe that there is value in limiting the dissection and the size of the incision in knee replacement surgery to MIS levels, but only to the extent that all of the knee can be well visualized. This means that an individual with a larger knee will need a slightly greater length of incision than the MIS level. It is more important to maximize the outcome than minimize the incision.
Pain control in Knee Replacement surgery
Knee replacement of any kind is a major operation. With this procedure there is potential for moderate to severe pain. The long term success of a knee replacement requires early range of motion, which is difficult if the knee hurts a lot. It is important for the surgeon to develop a pain management plan that prevents severe episodes of pain, while avoiding the strong side effects of nausea, dizziness, hypotension, and lethargy. The standard approach is the use of a general or spinal anesthesia followed by intravenous narcotics (PCA) for pain control.
A new more effective approach is the use multimodal pain therapy. In conjunction with the anesthesia department at Meriter hospital, we have developed a protocol for post-operative pain control utilizing intra-operative knee injections combined with an indwelling catheter femoral nerve block. Our patients have experienced better pain control in the first two days after surgery, avoiding severe pain episodes and using only a fraction of the narcotic pain medication. This is very beneficial in that the perioperative experience is better, the side effects associated with IV narcotics are less, and the early range of motion exercises are much less intimidating. Total knee patients that have had a previous knee replacement on the other side report a dramatic difference in the experience.
Using this technique, just before your surgery, the anesthesiologist will place a small catheter in the front of the hip area under local using ultrasound guidance. Numbing medication will be place into the catheter and you will notice the front of your knee area go numb. During surgery I will place a combination of pain medications into the tissues in the back of your knee while doing the knee replacement. The catheter is left in place for the first two days providing continuous analgesia to the front of the knee. On the second day post-op, when the pain levels are significantly less, the catheter is removed. Pain pills should be all that is needed at this point. The one warning with this technique is that the leg is weak on the first day post-op and you must have help when you get out of bed or you risk falling. During this day the physical therapy sessions concentrate on regaining range of motion in the knee. On the second day, the strength returns and walking with full weight bearing on the knee is added.
