The knee joint can be thought of as a hinge joint with the primary motion of straightening and bending. In reality, it is more complex than a simple hinge, as the surfaces actually glide and roll upon one another. It is composed of the end of the thigh bone (femur), the top of the leg bone (tibia), and the kneecap (patella).
The Knee Joint
The ends of the bone are covered with a smooth, glistening layer called articular cartilage. The articular cartilage is what allows the bones to glide smoothly with less resistance than ice sliding on ice. The articular cartilage can be seen on x-ray as the space in between the bones.
X-Ray of a Normal Knee Joint
The knee can be thought of as having 3 compartments - the medial, the lateral, and the patellofemoral. In addition, there are 2 special cartilages within the knee joint called the lateral and medial meniscus, which act as shock absorbers within the knee joint. There are also 2 ligaments within the knee, called the anterior cruciate ligament and the posterior cruciate ligament, which contribute to knee stability.
Arthritis of the knee is a condition in which there is loss of the articular cartilage of the femur, tibia, or patella. This can be seen on x-ray as a loss of the space between the two ends of bone.
X-Ray of an Arthritic Knee
Because of the loss of the gliding surfaces of the bone, people with arthritis may feel as though their knee is stiff and their motion is limited. Sometimes people actually feel a catching or clicking within the knee. Generally, loading the knee joint with activities such as walking long distances, standing for long periods of time, or climbing stairs makes arthritis pain worse. When the arthritis has gotten to be severe, the pain may occur even when sitting or lying down. The pain is usually felt in the inside part of the knee, but also may be felt in the front or back of the knee. As the cartilage is worn away preferentially on one side of the knee joint, people may find their knee will become more knock-kneed or bow-legged.
Arthritis of the knee usually occurs in people as they enter their 60's-70's, but this is variable depending upon factors such as weight, activity level, and knee anatomy. Arthritis may be caused by a variety of factors, including simple wear and tear, inflammatory disorders such as lupus or rheumatoid arthritis, infections, and post-traumatic. People who have had prior injury to their knee, damaging the meniscus or cruciate ligament may also develop arthritis. The end result of all these processes is a loss of the cartilage of the knee joint, leading to bone rubbing against bone.
Depending upon the severity of arthritis and the patient's age, knee arthritis may be managed in a number of different ways. Treatment may consist of operative or non-operative methods, or a combination of both.
The first line of treatment of knee arthritis includes activity modification, anti-inflammatory medication, and weight loss. Giving up activities that make the pain worse may make this condition bearable for some people. Anti-inflammatory medications such as ibuprofen, naprosyn and newer Cox-2 inhibitors help alleviate the inflammation that may be contributing to the pain.
Physical therapy to strengthen the muscles around the knee may help absorb some of the shock imparted to the joint. This is particularly true for knee-cap (patello-femoral) arthritis. Special kinds of braces, designed to place transfer load to a part of the knee that is less arthritic may also help relieve the pain. Injections of medication inside the knee joint may also help alleviate the pain temporarily.
Furthermore, walking with a cane in the hand on the opposite side as the painful knee may help distribute some of the load, reducing the pain. Finally, weight loss helps decrease the force that goes across the knee joint.
A combination of these non-operative measures may help ease the pain and disability caused by knee arthritis.
If the non-operative methods have failed to make your condition bearable, surgery may be the best option to treat knee arthritis. The exact type of surgery depends upon your age, anatomy, and underlying condition. Some examples of surgical options to treat arthritis include an osteotomy, which consists of cutting the bone to realign the joint; and knee replacement surgery.
Knee Replacement Implant
An osteotomy is a good alternative if the patient is young and the arthritis is limited to a one area of the knee joint. It allows the surgeon to realign the knee to unload the arthritic area and place weightbearing on relatively uninvolved portions of the knee joint. For example, a patient who has begun to become more bow-legged might be realigned to be more knock-kneed in order to redistribute the load across the joint. The advantage of this type of surgery is that the patient's own knee joint is retained and could potentially provide many years of pain relief without the disadvantages of a prosthetic knee. The disadvantages include a longer rehabilitation course and the possibility that arthritis could develop in the newly aligned knee.
Picture of Implant in Knee
Knee replacement surgery involves cutting away the arthritic bone and inserting a prosthetic joint. All of the arthritic surfaces are replaced, including the femur, tibia, and patella. The arthritic surfaces are removed, and the ends of the bone are replaced with the prosthesis, like capping a tooth. The prosthetic component is generally made of metal and plastic surfaces which are designed to glide smoothly against one another.
X-ray of a Total Knee Arthroplasty
Total knee replacement surgery was first performed in 1968, and has evolved over the years into a reliable and effective way to relieve disabling pain and allow patients to resume their active lives. Improvements in surgical techniques and implant design and construction have helped make this one of the most successful orthopaedic procedures today. As the population has become older and remained more active, the need for total knee replacement continues to increase. Today, approximately 270,000 total knee replacements are done every year in the United States.
Many of the advancements in knee replacement surgery have taken place at the Hospital for Special Surgery. Improvements in the surgical technique and the design of new implants are a few of the contributions the surgeons of the Hip and Knee service have made.
Decision to Have Surgery
People often wonder when and why they should have their knee replaced. This is an individualized question that depends upon a person's activity level and functional needs. Many people with arthritis live with pain that prevents them from participating in activities that they love; others are so debilitated that they have difficult putting on their shoes and socks. Total knee replacement offers a solution to the problem of arthritis and is performed with the goal of pain relief and resumption of activity. After a rehabilitation from a successful total knee replacement, a patient can expect to have at least as much motion as prior to surgery, without pain. According to a study presented at the American Academy of Orthopaedic Surgeons, total knee replacement dramatically improves a patient's quality of life and significantly reduces his/her long-term treatment costs. This study found that not only was a total knee replacement cost-effective when compared with non-operative management, it also provided more function and a better quality of life.
A total knee replacement is considered a major operation, and the decision to undergo total knee replacement is not a trivial one. People usually decide to undergo surgery when they feel they can no longer live with the pain of their arthritis.
The Prosthetic Implant
The implant for a total knee replacement is composed of 4 parts: the tibial and femoral components, a plastic insert, and the patella. The tibial and femoral components are made out of metal, usually cobalt-chrome, and are used to cap the ends of the femur and tibia after the arthritic bone is removed. The plastic insert is made out of ultra high molecular weight polyethylene (UHMWPE) and fits into the tibial component, such that the highly polished surface of the femur glides against the plastic. The patella component is also made of UHMWPE, and glides against the front of the femoral component. All together, the components weigh about 1 to 2 lbs. They are generally fixed to the bone with cement.
The total knee replacement is performed in an operating room with a special laminar airflow system, which helps reduce the chance of infection. Your surgeon will be wearing a "spacesuit", also designed to reduce the chance of infection. The entire surgical team will consist of your surgeon, two to three assistants, and a scrub nurse.
The anesthesia for a total knee replacement is given through an epidural catheter, which is a small tube inserted into the back. This is the same type of anesthesia given to women in labor. You will be made numb from the waist down so that you will not feel anything. The catheter stays in for 1-2 days after the surgery to help with your post-operative pain control. During the course of the operation, you can be as awake or as sleepy as you want to be.
After the epidural block is administered, a tourniquet, or cuff, will be placed around your thigh. The tourniquet will be inflated during surgery to help reduce the loss of blood. The incision for a total knee replacement is made along the front of your knee. The incision will measure anywhere from 4 to 10 inches depending upon your anatomy.
The arthritic surfaces of the femur, tibia, and patella are exposed and removed with power instruments. In so doing, deformities of the knee are corrected, and the knee will appear straighter after surgery. The bone is prepared to receive the artificial knee joint, and then the prosthesis is inserted. During the closure, two drains are inserted around the operated area to assist with evacuation of blood. Staples are used to close the skin.
The entire operation will take from 1 to 2 hours. Afterwards, you will be brought to the recovery room, where your blood work and vital signs will be checked. Most patients can be brought to a regular room within a few hours; others will need to stay overnight in the recovery room, as determined by your surgeon and anesthesiologist. Patients generally stay in the hospital for 3-4 days following total knee replacement surgery.
Some of the risks of the surgical procedure include the loss of blood, formation of a clot in your leg, and the chance of infection. The overall incidence of these risks is very small. They should be discussed with your surgeon prior to proceeding with the operation.
Some of the risks of having a prosthetic knee include the chance that the parts may loosen or wear out over time, or the prosthesis may become infected. Again, these issues will be discussed with you by your surgeon.
A total knee replacement has a lifespan much like anything with mechanical parts. Its longevity depends upon a variety of factors, including patient weight, patient activity, and mechanical properties of the prosthesis. The question of how long a prosthesis will last has been studied in detail over the years. Current studies indicate that over 85 percent of prostheses will function well for 20 years.
Many new developments are occurring in the area of knee surgery. The Hip/Knee and Surgical Arthritis services are comprised of world-renowned surgeons who have made countless contributions to the advancement of the field. A few of the areas of interest include: the use of computers during surgery to improve the precision of the surgery, the development of a smaller incision to perform the surgery; and prevention of deep vein thrombosis after knee replacement surgery; and the development of new materials for the prothesis, such as ceramics, that may increase the longevity of the implant.
The Hip/Knee and Surgical Arthritis Services have numerous physicians who specialize in total knee replacement. For more information, click on the links to their biographical sketches.
Most patients will be asked to donate 1 to 2 pints of their own blood in the weeks preceding knee replacement surgery. This helps reduce the need for a blood transfusion from our blood bank. Almost all of the patients will receive the donated blood as a transfusion after surgery. Rarely, an additional transfusion is necessary from our blood bank. The blood from the blood bank is carefully screened to the best of our ability to detect any infectious diseases.
You will be asked to see a medical doctor at HSS prior to your surgery. This is a precaution to make certain that you are healthy enough to undergo knee replacement surgery. In the course of this workup, you may be asked to have additional testing to examine your heart and lung function. After your surgery, this medical doctor will see you in the hospital.
Immediately after total knee replacement surgery, you will be in the recovery room. Most patients are able to go to a regular room after a few hours, when the sensation returns in your legs. You will be given a pain pump connected to your epidural catheter which will allow you to control when you are given pain medicine. Most people are quite comfortable with the pain pump in place.
On the day of surgery, you may do some of the exercises as instructed by your physical therapist, including quadriceps contractions and moving the feet up and down. Depending on your surgeon's preference, you may begin bending your new knee right after surgery, or on the first day after surgery. You will be allowed to take some ice chips after surgery to wet your mouth, but drinking liquids or eating may cause you to become nauseated. You will have a catheter in your bladder so that you do not have to worry about urinating. Once you regain the movement in your feet, you may be allowed to sit up, stand, and take a few steps with the assistance of a walker and a therapist.
The first day after surgery will be an active one, designed to help you get more mobile. You will meet our physical therapists, who will instruct you in more exercises to perform while in bed. In addition, they will help stand today and take a few steps with a walker. Generally, you will be allowed to drink clear liquids today.
In the next few days, you will find it easier and easier to move about. You will be freed up from the pain and urinary catheters. Pain medication will be given in the form of tablets. Eventually you will progress to walking with a cane or crutches. On the second day after surgery, if your bowels have shown evidence of recovery, you will be allowed to eat regular food.
Depending upon your age, pre-operative physical condition, and insurance coverage, you may be a candidate for short-term placement in a rehabilitation facility. Otherwise, you will be discharged home and a physical therapist will come to your house to continue rehabilitation. A case manager will discuss these options with you and help you plan for your eventual return home.
Your return to activity will be guided by your surgeon and therapists. Generally, patients are able to walk as much as they want by 6 weeks post-operatively. Patients are able to resume driving at 6 weeks. At 8 weeks, patients are able to resume playing golf and swimming; at 12 weeks, they may play tennis. Your surgeon will help you decide what activities you may resume.
Q: What is arthritis and what causes it?
A: Arthritis is an umbrella term for a number of disease entities in which the joints become inflamed and the cartilage that lines the bones deteriorates. Eventually, bone on bone wear occurs. As the disease progresses, patients often experience pain, stiffness, and disability. The vast majority of people diagnosed have osteoarthritis and in most cases the cause of their condition cannot be identified. One or more joints may be affected. Rheumatoid Arthritis (and other forms of inflammatory arthritis) is a disease that affects the entire system and multiple joints. This type of arthritis is an autoimmune disorder in which the body perceives the cartilage to be a foreign substance and attacks it.
Q: If I have arthritis in one knee, will I get it in the other?
A: If you have been diagnosed with osteoarthritis, having an affected knee does not mean that you will develop arthritis in the opposite knee. About 40 percent of patients who have osteoarthritis in one knee will have the same condition in the other knee. In contrast, patients with rheumatoid arthritis often develop problems in both knees.
Q: Why is my knee becoming more bow-legged or knock-kneed?
A: The increasing deformity of becoming more bow-legged or knock-kneed represents the greater wearing out of cartilage and bone from one side of the knee as compared to the other.
Q: What is that cracking sound I hear in my knee?
A: The cracking sound represents the rough surfaces rubbing against one another. Instead of smooth cartilage sliding against cartilage, arthritic bone is rough and irregular, and will not glide well.
Q: What kinds of things besides surgery can I do to help?
A: Modifying your activities to avoid those that bring on the pain may make your knee condition more bearable. In addition, losing weight will greatly decrease the forces across the knee joint, also reducing pain.
Q: Are there any exercises that will help my knee arthritis?
A: Physical therapy often does help in early stages of arthritis of the knee. Your orthopedic surgeon can teach you some of these exercises that focus upon strengthening the quadriceps muscle. In addition, your surgeon may prescribe physical therapy for your knee to give you a structured program to follow.
Q: Why should I have my knee replaced?
A: The decision to have a knee replacement is a personal one, and must take into account the risks and benefits of the procedure. Most patients will elect to have a total knee replacement when they can no longer bear the pain associated with their arthritis. Others will decide to have the surgery when they feel that their knee arthritis is preventing them from participating in activities that they enjoy.
Q: What is the prosthesis made of?
A: The implant for a total knee replacement is made of a combination of metal and plastic. The metal parts are generally composed of cobalt chrome, and the plastic is made of ultra high molecular weight polyethylene.
Q: Will I set off a metal detector?
A: While knee implants generally do not set off metal detectors, more sensitive machines may register the presence of the implant. Some physicians give their patients cards to show at the airport that explain that the bearer has received a knee prosthesis containing metal.
Q: How long does the operation take?
A: The operation generally takes between 1 to 2 hours.
Q: If both my knees have arthritis, can I have both replaced at the same time?
A: Yes, healthy patients younger than 75 years old, with no cardiopulmonary disease may be candidates for such surgery. Your orthopedist can tell you more about what is involved.
Q: What kind of anesthesia is used?
A: Most total knee replacements at Hospital for Special Surgery are performed under regional anesthesia. It is called an epidural block, which is the same kind of anesthesia given to women in labor. The epidural anesthesia provides numbness from the waist down, so there will be no pain during surgery. In addition, patients are given a light sedative to make them as sleepy or awake as they want to be.
Q: When will I be able to return to activity?
A: Your return to activity will be guided by your surgeon and therapists. Generally, patients are able to walk as much as they want by 6 weeks post-operatively. Patients are able to resume driving at 6 weeks. At 8 weeks, patients are able to resume playing golf and swimming; at 12 weeks, they may play doubles tennis.
Q: How long will the replacement last?
A: Current studies indicated that about 85 percent of prostheses will function well for 20 years. If your prosthesis wears out you may be a candidate for a second knee replacement.
Read more information regarding what to expect from your knee replacement surgery at HSS.
Contact the Hip and Knee Service at HSS for additional information.
Reviewed and Updated: 6/14/2010
Originally Published: 10/1/2002
Diagnostic imaging examinations provided by HSS Radiologists Images © Zimmer, Inc. Used by permission only.