KNEE REPLACEMENT - OVERVIEW

source: Steadman-Hawkins

• The knee is composed of the medial compartment including the medial meniscus, and the lateral compartment including the lateral meniscus. It acts as the hinge point during knee rotation and flexion / extension (bending/straightening).
• There is also the patellofemoral compartment, which is located under the patella (kneecap).

• The function of the knee is to provide stability and flexibility to the lower leg while walking, running, stair climbing, and rising from a seated position. It moves in bending, straightening, and rotation.
• These movements describe the normal kinematics (function) of the knee. Ligament disruption (such as anterior cruciate ligament injury) can compromise the stability of the knee in the anterior (front) and posterior (rear) direction as well as in rotation.
• If the meniscal cartilage is removed, early arthritis may occur.

• Osteoarthritis is a degenerative condition that may affect many joints throughout the body. It causes changes in the cartilage structure that lead to its breakdown. Over time, complete loss of articular cartilage (on the ends of the bones) can occur. Changes in the underlying bone and cartilage loss can result in joint space narrowing, peripheral osteophytes (bone spurs), loss of motion, pain, and disability.

• Rheumatoid Arthritis is a systemic disease that affects the lining of all joints in the body. It causes an inflammatory response in the joint lining which destroys the articular cartilage and surrounding tissues.

 What is knee arthritis and what does it do?

• Knee arthritis affects all cartilage in the knee.
• It leads to both biomechanical and biochemical change that impairs the function of the cartilage.
• The cartilage surfaces on the end of the femur, on top of the tibia, and under the patella are responsible for distributing the weight of the body, shock absorption, and knee joint lubrication. They are all impaired by the degenerative changes of arthritis.
• If there is a loss of cartilage surface, the function of the joint will degenerate over time.

Knee arthritis can lead to stiffness, poor function, physical deformity, and increasing pain. The ability to exercise or even walk for any length of time may also be affected. The grade of severity of arthritis is best determined in an arthroscopic procedure (A tiny instrument is used to look inside the knee joint).

Grade 1: Early changes show fissuring (breaks) in the cartilage
Grade 2: More extensive full thickness breaks in the cartilage
Grade 3: Intermittent loss of cartilage with breaks
Grade 4: Exposed subchondral (below the cartilage) bone

• Related conditions include poor alignment of the lower extremities, injury to knee cartilage and long term ligament instability.
• Other medical conditions that affect all joints of the body such as ankylosing spondylitis, rheumatoid arthritis or other systemic conditions can also cause degenerative changes in the knee.

• Knee pain and swelling begin to occur after physical activity.
• These symptoms gradually increase and eventually are present even at rest.
• In severe cases patients may have pain at night, as well as during the day.
• Motion in the joint decreases, and straightening and bending the knee becomes severely limited.
• Arthritis can cause crepitus, which is a grinding noise in the knee during motion.
• Other symptoms include an inability to walk for long distances, difficulty rising from a chair, climbing stairs, and eventually, difficulty with routine activities.

• Patients with knee arthritis usually describe a gradual onset of knee pain, restricted motion and activities, and pain at rest.

Findings of knee arthritis may include:

• painful gait on the involved side which causes a limp.

• a a knock-kneed or bowlegged condition. Most often there is a loss of complete extension (flexion contracture), and the inability to fully bend the knee.

• Very often there is swelling.

• Frequently bone spurs may be felt on the inside or outside of the joint.

• When the knee is moved through a range of motion, crepitus is present.

• There is usually tenderness around the inside and outside portions of the joint line.
  
  It is important to distinguish knee arthritis from hip arthritis or disc degeneration in the lumbar spine, since the symptoms are similar.

Usually, plain X-rays will show the presence of arthritis and any abnormalities in the alignment of the lower leg and changes in the mechanical axis. MRI scanning is usually not necessary to diagnose knee arthritis. There are four classic features of knee arthritis:

• Joint space narrowing

• Flattening of the femoral condyle (the end of the femur)

• Subchondral sclerosis (reactive bone thickening)

• Peripheral bone spur formation

Conservative treatment options are always tried first. These include:

• activity modification.
• exercise and conditioning.
• anti-inflamatory medication.
• Physical therapy programs in water (aquatic therapy) allow patients to exercise in non-weightbearing situations.
• Shock-absorbing shoe inserts often relieve some pain during activities.
• The injection into the joint of either cortisone or newer visco supplements such as hyaluronic acid may provide temporary relief for moderate to severe conditions.
• neoprene sleeves and other dynamic braces to correct mal-alignment of the leg.

Patients having night pain, difficulty walking or performing normal activities may be candidates for surgery. Operative treatments may include:

• arthroscopy and debridement (removal) of loose chondral fragments in the joint lining if the patient has symptoms such as pain and swelling.
• osteotomy, which corrects the mal-alignment of the lower leg.

• Finally, knee replacement surgery may dramatically relieve the symptoms of knee arthritis.

Total Knee Replacement

• Total knee replacement is an option for the patient who has not improved after trying the conservative measures described above and whose quality of life is severely affected.

• In knee replacement surgery all diseased cartilage is removed, and a metal and plastic prosthesis or replacement, is inserted. It is attached to the bone with bone cement or ingrowth of bone into the prothesis. The surgery takes one to two hours and requires a three to five day hospital stay.

• The results of knee replacement surgery are reliable, and over 95% of patients report good to excellent results at ten years.

• The incision must be kept clean and dry for the first 2 weeks after surgery to allow for healing.
• 2 to 3 weeks after the operation, sutures or staples are removed during an office visit.
• During the recovery process, most patients use: some form of walking aid such as a walker, crutches, or a cane for 6 to 8 weeks following knee replacement surgery. NSAIDS (anti-inflammatory medicines) and water therapy to enhance the results of surgery by maintaining muscle tone and range of motion. Significant physical therapy is added 1-2 days after surgery to strengthen the muscles around the knee and achieve full range of motion.
• In some cases, the symptoms of knee arthritis may disappear as early as 2 to 3 weeks after surgery, but it may take up to 6 months to achieve full recovery. Usually throughout this time pain steadily decreases.
• The physician will check the patient's range of motion and functional status six to eight weeks after surgery. The prosthesis should be examined annually for loosening or wear.

• infection of the joint, which usually requires additional surgery and treatment with antibiotics.
• If the wound doesn't heal properly, or the replacement components loosen, an additional surgery will be required.
• Medical complications such as deep venous thrombosis (blood clots) can occur.
• Existing heart, lung, and kidney problems can worsen.
• Fractures around the prosthesis may also require additional surgery.

• Older age is not a strict criterion for knee replacement.
• Incapacitating pain, limited function, and poor quality of life due to degeneration of the joint from arthritis are the indications for knee replacement.

• Modern knee replacements have a 90-95% survival rate at 15 years.

• The hospital stay is 3-5 days. Walking usually begins the first day after surgery.
• A walker or crutches are used for 6-8 weeks, and full recovery takes 4-6 months.
• Pain relief is usually noticed within 3 weeks during walking.