Revision Knee Replacement

Definition

Knee revision surgery, which is also known as revision total knee arthroplasty, is a procedure in which the surgeon removes a previously implanted artificial knee joint, or prosthesis, and replaces it with a new prosthesis. Knee revision surgery may also involve the use of bone grafts. The bone graft may be an autograft, which means that the bone is taken from another site in the patient's own body; or an allograft, which means that the bone tissue comes from another donor.

Purpose

Knee revision surgery has three major purposes: relieving pain in the affected hip; restoring the patient's mobility; and removing a loose or damaged prosthesis before irreversible harm is done to the joint. Knee prostheses can come loose for one of two reasons. One is mechanical and is related to the fact that the knee joint bears a great deal of weight when a person is walking or running. It is unusual for the metal part of a knee prosthesis to simply break. This part, however, is inserted into the upper part of the tibia, the larger of the two bones in the lower leg, after the surgeon has removed the upper surface of the tibia. The bone tissue that receives the metal implant is softer than the bone that was removed, which means that the metal implant may sink into the softer bone and gradually loosen.

The second reason for loosening of a knee prosthesis is related to the development of inflammation in the knee joint. The plastic part of a knee prosthesis is made of a material called polyethylene, which can form small particles of debris as a result of wear on the prosthesis over time. If the patient has an uneven gait, or pattern of walking, the debris particles tend to form at a faster rate because one side of the prosthesis will tend to pull away from the bone and the other side will be pushed further into the bone. These tiny fragments of plastic are absorbed by tissue cells around the knee joint, which become inflamed. The inflammatory response begins to dissolve the bone around the prosthesis in a process known as osteolysis. As the osteolysis continues, bone loss accelerates and the prosthesis eventually comes loose.

A knee prosthesis that has become infected or completely dislocated must be removed and replaced to prevent permanent damage to the patient's knee.

Demographics

The demographics of knee revision surgery are somewhat difficult to evaluate because the procedure is performed much less frequently than total knee replacement (TKR). TKR itself is a relatively new operation; the first total knee replacement was performed in the United Kingdom in 1968 and the first TKR in the United States in 1970. As of 2003, it is estimated that 98% of knee prostheses are still functioning well 10 years after surgery, with 94% still working after 20 years. Because of this high success rate, the number of patients who have had knee revision surgery yields a much smaller database than those who have had TKR. It is estimated that about 22,000 knee revision operations are performed in the United States each year; over half of them are done within two years of the patient's TKR.

Another difficulty in evaluating the demographics of knee revision surgery is the growing trend toward TKR in younger patients. A Canadian survey released in January 2003 stated that the number of knee replacements performed in patients below the age of 55 rose 90% between 1994 and 2001. As the number of knee replacement procedures done in younger patients continues to rise, the number of revision surgeries will increase as well. A study done in the United States in 1996 reported that women were almost twice as likely as men to have knee revision surgery, and that Caucasians were 1.5 times as likely as African Americans to have the procedure. This study, however, was limited to patients over the age of 65, so that its findings are not likely to be an accurate picture of younger patient populations.

Description

Although no revision surgery is easy or simple, there are different kinds of revisions. Sometimes only some of the parts need to be replaced and in other cases, all the parts need to be removed and the bone around the knee needs to be re-built with artificial bone. Below are a few examples of revison knee replacements:

Pre Simple

EXAMPLE BEFORE SURGERY: patient with severe arthritis involving the Right Knee and an implant on the Left side that is greater than 15 years old and loose requiring revision.

Post Simple

EXAMPLE AFTER SURGERY: patient after Right Knee revision and Bone reconstruction of the Femur

Pre Complex

EXAMPLE BEFORE SURGERY: patient has had a revision on the right and a standard TKA on the left. Patient needs a revision on the right for an infection.

Post Complex

EXAMPLE AFTER SURGERY: patient has had a complex revision with a tumor or endoprothesis type implant.

Most knee revision operations take about three hours to perform and are similar to knee replacement procedures. After the patient has been anesthetized, the surgeon opens the knee joint by cutting through the joint capsule. The first step in revision surgery is the removal of the old femoral component of the knee prosthesis. After the metal shell has been removed, the damaged bone at the end of the femur is scraped off and the femur is reshaped. If the bone is weak, the surgeon may decide to fill the cavity inside the femur with bone grafts. In some cases, metal wedges may be used to strengthen the attachment of the new femoral component.

After the new femoral component has been glued in place with bone cement, the old implant in the tibia is removed and the bone is reshaped to receive a new implant. If the old implant had loosened because it had moved downward into the softer tissue inside the tibia, the surgeon will pack the space with morselized bone from a donor before putting in the new implant. This technique is known as impaction grafting. The impaction grafting may be reinforced with wire mesh. If the tibia has been shortened by the removal of damaged bone, the surgeon will insert a wedge along with the new tibial implant and secure them to the end of the tibia with bone cement. A new plastic plate will be fastened to the tray at the top of the tibial implant so that the patient's femur can move smoothly over the tibia. If the patient's patella (kneecap) has been damaged, the surgeon will resurface its back surface and attach a plastic component to protect the patella from further bone loss. The tibial and femoral components of the prosthesis are then fitted together, the kneecap is replaced, and the knee tendons reattached with surgical wire. The knee joint is washed out with sterile saline fluid and the various layers of the incision closed.

Revision surgery on an infected knee requires two separate operations. In the first operation, the old prosthesis is taken out and a block of polyethylene cement known as a spacer block is inserted in the joint. The spacer block has been treated with antibiotics to fight the infection. The incision is closed and the spacer block remains inside the patient's knee for about six weeks. The patient is also given intravenous antibiotics during this period. After the infection has cleared, the knee is reopened and the new revision prosthesis is implanted.

Diagnosis/Preparation

In most cases, increasing pain, stiffness, and loss of mobility in the knee joint are early indications that the patient may benefit from revision surgery. The location of the pain may point to the part of the prosthesis that has been affected by osteolysis. Pain around or in the kneecap is not always significant by itself because many TKR patients have occasional discomfort in that area after their knee replacement. If the pain is diffuse (felt throughout the knee rather than in only one part of the knee), it may indicate either an infection or loosening of the prosthesis. Pain felt throughout the knee accompanied by tissue fluid accumulating in the joint points to a problem with the polyethylene part of the prosthesis. Pain in the lower thigh or in the part of the leg just below the knee suggests that the metal plate attached to the femur or the metal implant in the tibia may have come loose.

The doctor may take risk factors into account in assessing the likelihood of a failed knee prosthesis. Six factors have been identified as increasing a patient's risk of needing revision surgery within two years of knee replacement surgery:

  • age (Younger patients tend to be more active and to wear out knee prostheses more rapidly than older ones.)
  • a long hospital stay for the original knee surgery
  • concurrent diseases or disorders
  • any type of arthritis
  • surgical complications during the first knee operation
  • having the first knee operation performed at an urban hospital

The doctor will then usually order a series of imaging tests to determine the location of the problem and the extent of bone loss. X-ray studies can be used to check for complete dislocation of the prosthesis as well as loosening. Computed tomography appears to be more effective in detecting the early stages of osteolysis than x-ray studies. If the doctor suspects that the knee prosthesis has become infected, he or she will aspirate the joint. Aspiration is a procedure in which fluid is withdrawn from a joint through a needle and sent to a laboratory for analysis. The fluid will be cultured in order to identify the specific organism causing the infection.

Aftercare

Aftercare following knee revision surgery is essentially the same as for knee replacement, consisting of a combination of physical therapy, rehabilitation exercises, pain medication when necessary, and a period of home health care or assistance.

The length of recovery after revision knee surgery varies in comparison to the patient's first knee replacement. Some patients take longer to recover from revision surgery, but others recover more rapidly than they did from TKR, and they experience less discomfort. The reasons for this variation are not yet known. As of 2003, the Hip and Knee Center at Columbia University is conducting a study of 100 knee revision patients at five different sites in the United States in order to evaluate the outcomes of revision surgery. The patients will be examined at three-month, six-month, 12-month, and 24-month intervals in order to measure their progress after surgery.

Risks

The complications that may follow knee revision surgery are similar to those for knee replacement. They include:

  • Deep vein thrombosis.
  • Infection in the new prosthesis.
  • Loosening of the new prosthesis. The risk of this complication is increased considerably if the patient is overweight.
  • Formation of heterotopic bone. Heterotopic bone is bone that develops at the lower end of the femur following knee replacement or knee revision surgery. Patients who have had an infection in the joint have an increased risk of heterotopic bone formation.
  • Bone fractures during the operation. These are caused by the force or pressure that the surgeon must sometimes apply to remove the old prosthesis and the cement that may be attached to it.
  • Dislocation of the new prosthesis. The risk of dislocation is twice as great for revision surgery as for TKR.
  • Difference in leg length resulting from shortening of the leg with the prosthesis.
  • Additional or more rapid loss of bone tissue.

Normal results

Normal results of knee revision surgery are quite similar to those for TKR. Patients have less pain and greater mobility in the affected knee, but not complete restoration of the function of a normal knee. Between 5% and 20% of patients report some pain following either TKR or revision surgery for several years after their operation. Most patients, however, have considerably less discomfort in the knee after surgery than they did before the procedure. A recent British study found that revision knee surgery patients had the same positive results at six-month follow-up as patients who had had primary knee replacement surgery.

As with knee replacement surgery, patients who have had revision surgery may experience mild swelling of the leg for as long as three to six months after surgery. Swelling can be treated by elevating the leg, applying an ice pack, and wearing compression stockings.

Morbidity and mortality rates

The 30-day mortality rate following knee revision surgery is low, between 0.1% and 0.2%. The estimated rates of complications are as follows:

  • deep infection: 0.97%
  • loosening of the new prosthesis: 10–15%.
  • dislocation of the new prosthesis: 2–5%.
  • deep venous thrombosis: 1.5%

If you are experiencing problems with your knee replacement and would like to speak with Dr. Matthys, please visit our locations page or call 701-241-9300 to schedule your consult.