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LOOSENING OF THE TOTAL KNEE
What is a failed loose total knee replacement?
A painful total knee which restricts the patientís daily activities severely is a failed total knee joint. A failed total knee involves also severe psychical burden for the patient.
The majority of loose failed total knee joints have distinct changes apparent on the conventional X-ray pictures.
How will I know the failed loose total knee?
The surest sign of a loose total knee is increasing and lasting pain and stuffiness in the total knee. The patient will usually notice increasing pain in and around the artificial knee joint, difficulty to put weight on the knee joint, and diminished motion in the joint. The discomfort and pain usually develop slowly, years after the successful operation.
In the minority of patients, however, the total knee joint was never functioning well, and the pain and other discomfort only increased steadily since the operation.
Patients with a loose total knee joint limp.
The pain is usually felt in the whole knee area. The pain is often accompanied by increasing stiffness and effusion in the knee joint.
The patients with failed kneecap prosthesis feel the pain mainly in the front of the knee
On X-ray pictures of a loose knee joint there are one or more radiolucent lines around the contours of the artificial knee joint. The surgeon usually takes repeated X-ray pictures to assess the development of the radiolucent lines.
If the radiolucent lines increase in width on successive X-ray pictures the diagnosis of aseptic loosening is confirmed. Sometimes, the total knee prosthesis changes its position on successive X-ray pictures, which is another sign that the prosthesis has lost its fixation to the skeleton.
There is a special X-ray method called X-ray stereofotogrammetry that can measure the changes in the position of the total knee joint relative to the skeleton very accurately. This method can discover incipient loosening very early. Unfortunately, this method is difficult to implement, needs a special equipment and is used only on special clinics for research purposes.
Other methods to verify loosening of the total knee, such as bone scan, are less precise.
PICTURE : Loose total knee
Click on the icon for a full size picture.
In this picture the left side shows a firmly seated total knee. The total knee prosthesis is in direct contact with the skeleton. The X-ray picture shows direct contact of the white shadows of the knee prosthesis with the white shadow of the skeleton.
The prosthesis on the right side is loose, both components lost their contact with the surrounding skeleton. The components are surrounded by loose connective tissue.
Lower row: The connective tissue is pervious for X-rays, so that on the (negative) X-ray pictures the white shadows of the prosthesis are surrounded by a dark area of the loose connective tissues, by "lucent lines".
The white shadows of the skeleton around the prosthesis have been "eaten up" by the dark shadows of the connective tissue = osteolysis. Both components changed position.
When is a revision operation for a loose total knee necessary?
Reasons for a revision operation of a failed loose total knee are
loss of function
progress of osteolysis
The first two reasons for revision operation are much like the reasons for the primary total knee replacement. The third reason, progress of osteolysis, is, however, of overriding importance for your decision. The progress of the osteolysis, the dissolving bone disease that caused the failure of the total knee, is namely unpredictable. There is always a risk that osteolysis will destruct large areas of the skeleton around the total knee joint if you will wait too long.
There is a small group of patients where the osteolysis can proceed without pain. In these patients the osteolysis has been discovered by chance on the X-ray pictures only. These osteolytic changes may lead to a fracture if they are extensive. Such extensive osteolysis that may cause bone fracture around the prosthesis should be treated with a revision operation, although the patient does not have pain.
Risk of fracture
In patients with skeletons weakened by osteolysis around the failed total knee joint, there is always the risk that the weak skeleton may succumb to a fracture. Fracture through the skeleton which is already weak adds another challenge to the already difficult revision operation. Donít take the risks.
Patients with grave medical condition that precludes a new operation of the loose total knee joint are left without a revision operation. Usually, the grave medical condition restricts the mobility of these patients substantially so that the risk of the skeleton fracture is lower in these patients.
Treatment of aseptic loosening .
Not every total knee joint with "lucent lines" on an X-ray picture evokes pain and stiffness.
Many patients live happily with their well functioning total knee joints while the X-rays of their artificial joints show the lucent lines. Remember that the X-ray picture of your artificial joint and your personal comfort might not be correlated.
Loosening of a total knee prosthesis with little changes in the skeleton, with no progress of lucent lines, and with mild symptoms may be treated by "watchful observance". That means reduced weight bearing and repeated controls including X-ray pictures, while you and the surgeon wait with the decision to operate on your total knee.
If the patients experience increasing pain from their artificial joint and the X-ray pictures show signs of incipient aseptic loosening, the first step usually ordered by the surgeon is a restricted weight bearing regime. Often this may by all that is needed. The loose knee prosthesis may find a new stable position, the discomfort and pain disappears, and the radiolucent lines seen on the X-rays do not progress.
If the radiolucent lines on X-ray pictures widen and if the pain and other discomfort from the artificial knee joint increases then a revision operation becomes necessary. At this revision operation the surgeon will remove the loose prosthesis, remove carefully all loose tissue, and put in a new revision prosthesis. See more on these revision knee prostheses in the chapters Linked total knee prostheses .
How long can you wait with the revision operation?
There is always a risk that the loosening process will destruct too large parts of the skeleton if you wait too long. The revision operation may then be more difficult. So if you will wait, you should have a careful monitoring of the progress of the skeletal changes around your total joint.
There is a small group of patients where the osteolysis can proceed without pain. In these patients the osteolysis has been discovered by chance on the X-ray pictures only.
The surgeons are discussing whether regular controls with X-ray pictures of the total joint are necessary for all patients to discover these rare cases of "silent" osteolysis.
How is the revision operation done?
The surgeon opens the total knee joint and assess the stability of the total knee joint prosthesis and takes samples for bacteriological cultures.
If there is no suspicion of postoperative infection, the surgeon then removes the total knee component that is unstable. Usually, there is loose connective tissue around the unstable component. The surgeon must remove all loose connective tissue.
There are three components in every total knee joint ( femoral, tibial, and patellar component) and only one of them may be loose. There is still a debate whether it suffices to exchange only the loose component and let the stable component stay in place or whether all three components should be always exchanged.
The surgeon then places a new total knee prosthesis in the clean bony bed. Because the old total knee joint was exchanged with a new, this surgery is also called an exchange operation.
The main problem of the exchange operation is the management of the bone cavities caused by the osteolysis (bone dissolving disease). Cement cannot be used to fill these defects.
A new technique, called impaction grafting, uses small bone chips to fill large defects caused by osteolysis. The surgeon may take small bone chips from the patients own skeleton (from pelvic bones, e.g.) or use bone chips provided by the bone bank.
The bone chips are impacted into the defect and make a stable ground for a new total knee prosthesis. The surgeons may use bone cement to fix the new total knee joint in the bed of impacted small bone grafts. Usually the surgeon uses total knee prostheses with long shafts. These shafts will anchor the total knee prosthesis in the marrow cavities of the thigh- and shinbone. These long shafts will add stability to the new total knee prosthesis.
Picture: Revision total knee prosthesis.
(Click on the icon for a full size image)
Note the long shafts that anchor the prosthesis in the marrow cavities of the femur and tibia.
If the osteolysis is confined to a smaller area and the whole total joint is still stable, the surgeon can open the area of osteolysis only, remove the loose tissue, and pack the cavity with healthy bone chips. The total joint, which is stable, will stay in place.
If you wish more details about total knee loosening
Archibeck, J Bone Joint Surg-Am, 2000, 81-A, 1485www.nih.gov