• Osteoarthritis. This is an age-related «wear and tear» type of arthritis. It usually occurs in people 50 years of age and older, but may occur in younger people, too. The cartilage that cushions the bones of the knee softens and wears away. The bones then rub against one another, causing knee pain and stiffness.

 

• Rheumatoid arthritis. This is a disease in which the synovial membrane that surrounds the joint becomes inflamed and thickened. This chronic inflammation can damage the cartilage and eventually cause cartilage loss, pain, and stiffness. Rheumatoid arthritis is the most common form of a group of disorders termed «inflammatory arthritis.»

 

• Post-traumatic arthritis. This can follow a serious knee injury. Fractures of the bones surrounding the knee or tears of the knee ligaments may damage the articular cartilage over time, causing knee pain and limiting knee function.

There are four basic steps to a knee replacement procedure.

• 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.
• 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.
• 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.
• Insert a spacer. A medical-grade plastic spacer is inserted between the metal components to create a smooth gliding surface.

Candidates for Surgery

There are no absolute age or weight restrictions for total knee replacement surgery.

Recommendations for surgery are based on a patient’s pain and disability, not age. Most patients who undergo total knee replacement are age 50 to 80, but orthopaedic surgeons evaluate patients individually. Total knee replacements have been performed successfully at all ages, from the young teenager with juvenile arthritis to the elderly patient with degenerative arthritis.

• A medical history. Your orthopaedic surgeon will gather information about your general health and ask you about the extent of your knee pain and your ability to function.
• A physical examination. This will assess knee motion, stability, strength, and overall leg alignment.
• X-rays. These images help to determine the extent of damage and deformity in your knee.
• Other tests. Occasionally blood tests, or advanced imaging such as a magnetic resonance imaging (MRI) scan, may be needed to determine the condition of the bone and soft tissues of your knee.

Your orthopaedic surgeon will review the results of your evaluation with you and discuss whether total knee replacement is the best method to relieve your pain and improve your function. Other treatment options — including medications, injections, physical therapy, or other types of surgery — will also be considered and discussed.

In addition, your orthopaedic surgeon will explain the potential risks and complications of total knee replacement, including those related to the surgery itself and those that can occur over time after your surgery.

Two wedge-shaped pieces of cartilage called meniscus act as «shock absorbers» between your thighbone and shinbone. They are tough and rubbery to help cushion the joint and keep it stable.

The knee joint is surrounded by a thin lining called the synovial membrane. This membrane releases a fluid that lubricates the cartilage and reduces friction.

Rheumatoid arthritis is a chronic disease that attacks multiple joints throughout the body, including the knee joint. It is symmetrical, meaning that it usually affects the same joint on both sides of the body.

In rheumatoid arthritis the synovial membrane that covers the knee joint begins to swell, This results in knee pain and stiffness.

Rheumatoid arthritis is an autoimmune disease. This means that the immune system attacks its own tissues. The immune system damages normal tissue (such as cartilage and ligaments) and softens the bone.

Posttraumatic Arthritis

Posttraumatic arthritis is form of arthritis that develops after an injury to the knee. For example, a broken bone may damage the joint surface and lead to arthritis years after the injury. Meniscal tears and ligament injuries can cause instability and additional wear on the knee joint, which over time can result in arthritis.

• The joint may become stiff and swollen, making it difficult to bend and straighten the knee.
• Pain and swelling may be worse in the morning, or after sitting or resting.
• Vigorous activity may cause pain to flare up.
• Loose fragments of cartilage and other tissue can interfere with the smooth motion of joints. The knee may «lock» or «stick» during movement. It may creak, click, snap or make a grinding noise (crepitus).
• Pain may cause a feeling of weakness or buckling in the knee.
• Many people with arthritis note increased joint pain with rainy weather

Three bones meet to form your knee joint: your thighbone (femur), shinbone (tibia), and kneecap (patella). Your kneecap sits in front of the joint to provide some protection.

Bones are connected to other bones by ligaments. There are four primary ligaments in your knee. They act like strong ropes to hold the bones together and keep your knee stable.

Medial collateral ligament tears often occur as a result of a direct blow to the outside of the knee. This pushes the knee inwards (toward the other knee).

Blows to the inside of the knee that push the knee outwards may injure the lateral collateral ligament.

• Pain at the sides of your knee. If there is an MCL injury, the pain is on the inside of the knee; an LCL injury may cause pain on the outside of the knee.
• Swelling over the site of the injury.
• Instability — the feeling that your knee is giving way.

Infections are caused by bacteria. Although bacteria are abundant in our gastrointestinal tract and on our skin, they are usually kept in check by our immune system. For example, if bacteria make it into our bloodstream, our immune system rapidly responds and kills the invading bacteria.

However, because joint replacements are made of metal and plastic, it is difficult for the immune system to attack bacteria that make it to these implants. If bacteria gain access to the implants, they may multiply and cause an infection.

Despite antibiotics and preventive treatments, patients with infected joint replacements often require surgery to cure the infection.

The most common ways bacteria enter the body include:

• Through breaks or cuts in the skin
• During major dental procedures (such as a tooth extraction or root canal)
• Through wounds from other surgical procedures

Some people are at a higher risk for developing infections after a joint replacement procedure. Factors that increase the risk for infection include:

• Immune deficiencies (such as HIV or lymphoma)
• Diabetes mellitus
• Peripheral vascular disease (poor circulation to the hands and feet)
• Immunosuppressive treatments (such as chemotherapy or corticosteroids)
• Obesity

Signs and symptoms of an infected joint replacement include:

• Increased pain or stiffness in a previously well-functioning joint
• Swelling
• Warmth and redness around the wound
• Wound drainage
• Fevers, chills and night sweats
• Fatigue

Tests

Imaging tests. X-rays and bone scans can help your doctor determine whether there is an infection in the implants.

Laboratory tests. Specific blood tests can help identify an infection. For example, in addition to routine blood tests like a complete blood count (CBC), your surgeon will likely order two blood tests that measure inflammation in your body. These are the C-reactive Protein (CRP) and the Erythrocyte Sedimentation Rate (ESR). Although neither test will confirm the presence of infection, if either or both of them are elevated, it raises the suspicion that an infection may be present. If the results of these tests are normal, it is unlikely that your joint is infected.

Additionally, your doctor will analyze fluid from your joint to help identify an infection. To do this, he or she uses a needle to draw fluid from your hip or knee. The fluid is examined under a microscope for the presence of bacteria and is sent to a laboratory. There, it is monitored to see if bacteria or fungus grow from the fluid.

The fluid is also analyzed for the presence of white blood cells. In normal hip or knee fluid, there are a low number of white blood cells. The presence of a large number of white blood cells (particularly cells called neutrophils) indicates that the joint may be infected. The fluid may also be tested for specific proteins that are known to be present in the setting of an infection.

Osteonecrosis of the knee most often occurs in the knobby portion of the thighbone, on the inside of the knee (medial femoral condyle). However, it may also occur on the outside of the knee (lateral femoral condyle) or on the flat top of the shinbone (tibial plateau).

Osteonecrosis develops when the blood supply to a segment of bone is disrupted. Without adequate nourishment, the affected portion of bone dies and gradually collapses. As a result, the articular cartilage covering the bone also collapses, leading to disabling arthritis.

Osteonecrosis of the knee can affect anyone, but is more common in people over the age of 60. Woman are three times more likely than men to develop the condition.

Risk Factors

It is not always known what causes the lack of blood supply, but doctors have identified a number of risk factors that make someone more likely to develop osteonecrosis.

• Injury. A knee injury—such as a stress fracture or dislocation—combined with some type of trauma to the knee, can damage blood vessels and reduce blood flow to the affected bone.
• Oral corticosteroid medications. Many diseases, such as asthma and rheumatoid arthritis, are treated with oral steroid medications. Although it is not known exactly why these medications can lead to osteonecrosis, research shows that there is a connection between the disease and long-term steroid use. Steroid-induced osteonecrosis frequently affects multiple joints in the body.
• Medical conditions. Osteonecrosis of the knee is associated with medical conditions, such as obesity, sickle cell anemia, and lupus.
• Transplants. Organ transplantation, especially kidney transplant, is associated with osteonecrosis.
• Excessive alcohol use. Overconsumption of alcohol over time can cause fatty deposits to form in the blood vessels as well as elevated cortisone levels, resulting in a decreased blood supply to the bone.

Regardless of the cause, if osteonecrosis is not identified and treated early, it can develop into severe osteoarthritis.

Osteonecrosis develops in stages. The first symptom is typically pain on the inside of the knee. This pain may occur suddenly and be triggered by a specific activity or minor injury. As the disease progresses, it becomes more difficult to stand and put weight on the affected knee, and moving the knee joint is painful.

Other symptoms may include:

• Swelling over the front and inside of the knee
• Sensitivity to touch around the knee
• Limited range of motion in the joint

It may take from several months to over a year for the disease to progress. It is important to diagnose osteonecrosis early, because some studies show that early treatment is associated with better outcomes.

Magnetic resonance imaging (MRI) scans. Early changes in the bone that may not show up on an x-ray can be detected on an MRI. These scans are used to evaluate how much of the bone has been affected by the disease. An MRI scan may also show early osteonecrosis that has yet to cause symptoms (for example–ostenecrosis that may be developing in the opposite knee joint).

Bones are connected to other bones by ligaments. There are four primary ligaments in your knee. They act like strong ropes to hold the bones together and keep your knee stable.

Collateral ligaments. These are found on the sides of your knee. The medial collateral ligament is on the inside and the lateral collateral ligament is on the outside. They control the sideways motion of your knee and brace it against unusual movement.

Cruciate ligaments. These are found inside your knee joint. They cross each other to form an «X» with the anterior cruciate ligament in front and the posterior cruciate ligament in back. The cruciate ligaments control the back and forth motion of your knee.

The posterior cruciate ligament keeps the shinbone from moving backwards too far. It is stronger than the anterior cruciate ligament and is injured less often. The posterior cruciate ligament has two parts that blend into one structure that is about the size of a person’s little finger.

Many times a posterior cruciate ligament injury occurs along with injuries to other structures in the knee such as cartilage, other ligaments, and bone.

Injured ligaments are considered «sprains» and are graded on a severity scale.

Grade 1 Sprains. The ligament is mildly damaged in a Grade 1 Sprain. It has been slightly stretched, but is still able to help keep the knee joint stable.

Grade 2 Sprains. A Grade 2 Sprain stretches the ligament to the point where it becomes loose. This is often referred to as a partial tear of the ligament.

Grade 3 Sprains. This type of sprain is most commonly referred to as a complete tear of the ligament. The ligament has been split into two pieces, and the knee joint is unstable.

Posterior cruciate ligament tears tend to be partial tears with the potential to heal on their own. People who have injured just their posterior cruciate ligaments are usually able to return to sports without knee stability problems.

• A direct blow to the front of the knee (such as a bent knee hitting a dashboard in a car crash, or a fall onto a bent knee in sports)
• Pulling or stretching the ligament (such as in a twisting or hyperextension injury)
• Simple misstep

• Pain with swelling that occurs steadily and quickly after the injury
• Swelling that makes the knee stiff and may cause a limp
• Difficulty walking
• The knee feels unstable, like it may «give out»

During the physical examination, your doctor will check all the structures of your injured knee, and compare them to your non-injured knee. Your injured knee may appear to sag backwards when bent. It might slide backwards too far, particularly when it is bent beyond a 90° angle. Other tests which may help your doctor confirm your diagnosis include X-rays and magnetic resonance imaging (MRI). It is possible, however, for these pictures to appear normal, especially if the injury occurred more than 3 months before the tests.

X-rays. Although they will not show any injury to your posterior cruciate ligament, X-rays can show whether the ligament tore off a piece of bone when it was injured. This is called an avulsion fracture.

MRI. This study creates better images of soft tissues like the posterior cruciate ligament.

Anatomy

Three bones meet to form your knee joint: your thighbone (femur), shinbone (tibia), and kneecap (patella). Your kneecap sits in front of the joint to provide some protection.

Bones are connected to other bones by ligaments. There are four primary ligaments in your knee. They act like strong ropes to hold the bones together and keep your knee stable.

The anterior cruciate ligament can be injured in several ways:

• Changing direction rapidly
• Stopping suddenly
• Slowing down while running
• Landing from a jump incorrectly
• Direct contact or collision, such as a football tackle

Several studies have shown that female athletes have a higher incidence of ACL injury than male athletes in certain sports. It has been proposed that this is due to differences in physical conditioning, muscular strength, and neuromuscular control. Other suggested causes include differences in pelvis and lower extremity (leg) alignment, increased looseness in ligaments, and the effects of estrogen on ligament properties.

When you injure your anterior cruciate ligament, you might hear a «popping» noise and you may feel your knee give out from under you. Other typical symptoms include:

• Pain with swelling. Within 24 hours, your knee will swell. If ignored, the swelling and pain may resolve on its own. However, if you attempt to return to sports, your knee will probably be unstable and you risk causing further damage to the cushioning cartilage (meniscus) of your knee.
• Loss of full range of motion
• Tenderness along the joint line
• Discomfort while walking