When the knee joint is damaged by arthritis or injury, simple daily activities, such as walking or climbing stairs can become difficult. A total knee replacement is really knee cartilage replacement with an artificial surface. The knee itself is not replaced. An artificial substitute for the cartilage is inserted onto the end of each of the bones. This is done with a metal alloy on the end of the femur and tibia, with a medical-quality plastic inserted between them. The cartilage on the under-surface of the kneecap may also be replaced with plastic. Replacement of the worn cartilage with a metal and plastic implant creates a new, smoother cushion and a joint with improved function. Although technically not a normal knee, a replaced knee provides relief from the arthritis and injury pain. Most patients experience a significant decrease in their pain with progressive improvement in range of motion after knee replacement. These improvements provide an increased quality of life with a return to activities without the daily burden of joint pain.
The initial step when considering knee replacement surgery is to meet with a qualified, experienced orthopedic surgeon to see if you are a candidate for total knee replacement surgery. Your surgeon will take your medical history, perform a physical examination, and X-ray your knee. Often even with significant pain, and if X-rays reveal advanced arthritis within the knee joint, initial treatment is almost always non-surgical options.
Available treatment options prior to knee surgery may include weight loss if appropriate, an exercise program, medications, joint injections, or bracing. If there is no joint symptom improvements despite these measures, then you may be encouraged to consider surgery. Joint replacement is considered a major surgery, and the decision to move forward with surgery is not always straight forward and often involves a thoughtful conversation with yourself, your loved ones, and an experienced surgeon. The final decision rests with you and is typically based on the pain and disability from the arthritis influencing your quality of life and daily activities. Candidates for Total Knee Replacement surgery commonly report that their symptoms keep them from participating in activities that are important to them like walking, taking stairs, working, sleeping, etc.
A knee replacement (also called knee arthroplasty) might be more accurately termed a knee "resurfacing" because only the surface of the bones are actually replaced.There are four basic steps to a knee replacement procedure.
1. Prepare the bone. The damaged cartilage surfaces at the ends of the femur and tibia are removed along with a small amount of underlying bone.
2. Position the metal implants. The removed cartilage and bone is replaced with metal components that recreate the surface of the joint. These metal parts may be cemented or "press-fit" into the bone.
3. Resurface the patella. The undersurface of the patella (kneecap) is cut and resurfaced with a plastic button. Some surgeons do not resurface the patella, depending upon the case.
4. Insert a spacer. A medical-grade plastic spacer is inserted between the metal components to create a smooth gliding surface.
You will most likely be admitted to the hospital on the day of your surgery. After admission, you will be evaluated by a member of the anesthesia team. The most common types of anesthesia are general anesthesia (you are put to sleep) or spinal, epidural, or regional nerve block anesthesia (you are awake but your body is numb from the waist down). The anesthesia team, with your input, will determine which type of anesthesia will be best for you.
While general anesthesia is a safe option, both hip and knee replacements can be performed under regional anesthesia. Choices for regional anesthesia include spinal anesthesia, epidural anesthesia, or one of a variety of peripheral nerve blocks. Many surgeons and anesthesiologists prefer regional anesthesia because data shows it can reduce complications and improve your recovery experience with less pain, less nausea and less narcotic medicine required. Recently, peripheral nerve blocks have become more popular as an adjunct for pain control. For total knee replacement this can include an adductor canal block, which allows pain control without causing weakness of your muscles. You should have a discussion regarding anesthesia and post-operative pain management with your surgeon and anesthesia team prior to your surgery.
The orthopedic implant industry has developed a number of innovative technologies in an effort to improve the outcomes of total joint replacement surgery. In recent years, these technologies have been marketed directly to patients, which has increased the awareness as well as confusion on what these different designs mean. The most important message is that while a certain manufacturer may claim that their design is better, almost all of the available registry data (large collections of data that track total joint surgery outcomes) show that there is no clear advantage to any of these designs when it comes to improving outcomes. Here are specific implant design terms your surgeon may discuss:
Gender specific Joint Replacement Implant: This refers to a modified implant design that accounts for average anatomic differences between men’s and women’s knees. Most manufacturers have incorporated similar modifications in their newer designs, which allow for more sizing options so that the prosthesis can be more accurately fit to the patient’s native anatomy and recreate the natural function of the knee.
Rotating platform Joint Replacement Implant: This refers to a plastic bearing that independently rotates on a metal tray on which it is seated. More often, the plastic bearing locks into the metal tray – referred to as a “fixed bearing.” Some theoretical advantages to the rotating platform concept when it was initially designed was that it could reduce the wear of the plastic bearing, reduce the rate of loosening of the metal parts, and better replicate how a patient’s knee works (kinematics). Most current data shows that after five to ten years in use, there does not appear to be any difference between rotating platform and fixed bearing designs in any of these outcomes.