Knee Joint Replacement

The orthopedic procedure of knee joint replacement is called a total knee arthroplasty (TKA). This surgery involves replacing the existing knee joint with a manmade one. Orthopedic surgeons replace knee joints in order to end pain, stiffness, and loss of function.

Both chronic osteoarthritis and rheumatoid arthritis commonly cause people to lose knee function and damage the joint to the degree that they need a knee joint replacement (total knee arthroplasty or TKA). But knee damage may also stem from injury or infection. Sometimes, people with severe rheumatoid arthritis of the knee can require a TKA at an early age.

During knee joint replacement surgery, the damaged parts of the knee joint are removed and manufactured components (prosthesis) are then placed in the knee. The three areas involved are

• lower end of the thighbone (femur),
• upper end of the shinbone (tibia), and
• behind the kneecap (patella).

The prosthesis can have both metal and plastic parts. Some newer prostheses now are made of metal on metal, ceramic on ceramic, or ceramic on plastic.

The surgery for total knee replacement lasts about two hours and involves an incision over your knee. The thighbone and shinbone will be cut to prepare them for the new pieces. The patella will be moved at the beginning of the procedure, and later a bone cement will be utilized to fasten the prosthesis to it. This is the traditional way the procedure has been performed. Several modifications to the procedure can be made and partial knee replacements are options for certain joints, as well.

During the procedure, you will either have general anesthesia (when you are fully asleep) or a regional block (spinal or epidural with more localized anesthesia) that numbs your legs combined with an intravenous medication that will sedate you during the procedure. Your surgeon and anesthesiologist will discuss the advantages and disadvantages of both techniques.

You will usually leave the hospital within a few days of the procedure and attend a rehabilitation facility that will help you get used to your new knee and eventually help you return to all your activities and hopefully many that you gave up due to pain or inability of your "old" knee to handle.

The most common problems with a knee joint replacement are

• fractures (breaks) of the new knee after a fall or other accident,
• pain from slippage and wear in the new joint, and
• loosening of the prosthetic components.

Other less common problems include

• infection of the joint;
• dislocation, either complete or partial, of the new knee; and
• a blood clot in a vein (deep vein thrombosis) above or below the knee. (Clots occur most commonly shortly after replacement surgery.)

Many people who fall after having a knee replacement break the bone below the new joint on which the new knee is anchored. Pain and swelling occur at or near the site of the knee joint replacement.

Pain can occur gradually as the new joint develops wear patterns that interfere with the smooth function of the knee.

• Slippage can cause the prosthetic surfaces to move in opposition to each other and cause pain.
• This pain increases with activity and decreases when you sit.
• This pain of movement differs from the normal start-up pain that occurs in the first three to six months after knee replacement and that decreases over the first few steps.
• Infection will cause pain, along with frequent redness and swelling at the joint, even when you are at rest.
• Often fluid will collect at the knee joint in the presence of infection and cause a boggy swelling. Fluid may not accumulate with every infection.
• Fever may occur.

Dislocating the knee will cause pain.

• Deformity of the joint will be present.
• A dislocation may damage adjoining nerves, muscles, and blood vessels and impair their function. The popliteal artery, which carries the entire blood supply to your lower leg and foot, can be injured or pinched shut. This is a medical emergency and requires urgent evaluation and diagnosis. The symptoms are pain, the lower leg may turn pale and cold, have poor or no pulse, and the leg may swell.
• Nerves to your lower leg can be cut or injured, causing your lower leg to become numb (paresthesia), weak (paresis), or paralyzed.
• Blood clots tend to form during the period ("post-op" or "post-operatively") when you cannot move following a knee replacement.
  • Clots become progressively less common with time.
  • A clot in your vein generally causes new pain, swelling, or redness in your lower leg.
  • The greatest concern is that the clot will travel through your veins and could lodge in your lung (pulmonary embolism).

Call your family doctor or orthopedist if you develop gradual pain that feels like slippage in your knee. This generally is an urgent problem but not an emergency.

Call your doctor if you notice unexpected drainage from or poor healing of a recent surgery, increasing swelling, warmth, or fevers.

Go to the hospital's emergency department if you experience any of the following:

• A fracture or dislocation after a fall
• New swelling
• New pain while resting
• Redness or warmth at a joint, suggesting infection
• Swelling, pain, or redness below your knee that suggests a clot in your vein (deep venous thrombosis or DVT)

Your doctor will base your diagnosis on clinical examination and X-rays.

• A fracture usually involves a bone directly above or below your new knee. Most commonly your thighbone (femur) breaks just above its connection with the knee replacement.
• As the new joint begins to wear, your knee may not glide smoothly through its range of motion. You likely will notice that movements are painful now that were not painful in the past. An X-ray can help to determine if there is loosening or abnormal wear of prosthetic components.
• Pain from infection does not go away with rest, and fluid may begin to build up in the knee joint.
  • The doctor can sample any fluid through arthrocentesis, a procedure of drawing the fluid out of the affected joint with a needle and syringe. The removal of fluid will decrease the pain but more importantly the fluid will be sent to the laboratory for examination and to help make a decision if an infection is present and how to treat it.
  • Blood tests also may be performed.
• An X-ray can confirm a knee dislocation. A doctor must assess any damage to nerves, blood vessels, or muscles besides the dislocation itself.
• A blood clot often causes pain and swelling in your leg farther from your heart than where the clot sits. That area may become red and feel warm.
  • Your doctor may perform a Doppler ultrasound test, especially for a clot suspected to be above your knee. This evaluates the flow of blood in that area.
  • The doctor may also order a venogram of your leg. In this test, dye is injected into a vein, and X-rays are assessed to look for evidence of a blood clot in a deep vein of the leg. Without the dye, the veins would not show up on an X-ray.

• If you have broken a bone, the doctor will first immobilize your leg and then may repair the break surgically.
• If your knee replacement is worn and slipping, you likely will be given pain relievers until an orthopedist can determine if the knee joint prosthesis should be replaced.
• Infection in the joint calls for antibiotics, washing out the joint, and often replacing the joint.
• Doctors will reset any dislocation promptly to decrease the chance of damage to nerves or blood vessels.
• A confirmed clot is treated with anticlotting agents such as heparin (Hep-Lock, Liquaemin) or enoxaparin (Lovenox).

Follow your orthopedist's recommended schedule of visits and physical therapy. If emergency problems arise, go to an emergency department and then follow up with your orthopedist. The emergency doctor may contact your orthopedist during your emergency department visit to discuss and coordinate care. He or she may take X-rays or blood tests to help with your evaluation.

Most people are back to knee full function in three to six months after knee joint replacement. Those who are diligent about postoperative physical therapy tend to do better.

The costs of total knee joint replacement vary greatly from state to state and region to region. Costs are directly related to varying insurance coverages.

Prevention involves proper use of the new joint.

• You must follow the instructions given you in physical therapy.
• People with an unsteady gait who have a total knee arthroplasty (TKA) should consider using a cane or walker.

With proper care and rehabilitation, a total knee arthroplasty (TKA) may last 20 years or longer before you need a replacement. Most replaced knee joints continue to work 10 years after surgery.