Artificial knee replacement is quite common nowadays. As science and technology progresses, the lifespan of people is enhanced and more people need artificial joints. But, some of these joints wear away or it requires another total knee replacement. A normal knee replacement is expected to function well for over 15 years in around 80% of patients. However, some procedures fail and it may require a second surgery. This procedure is known as Revision Knee Replacement. It requires replacement of the previously failed knee prosthesis with a new one. The procedure is complex. It requires extensive preoperative planning, sophisticated implants and tools, prolonged operating times and mastery of difficult surgical techniques.
The knee joint is formed where the thighbone (femur) meets the shinbone (tibia). A slick cushion of articular cartilage covers the ends of both of these bones so that they slide against one another smoothly. The articular cartilage is kept slippery by joint fluid made by the joint lining (Synovial). The kneecap (patella) is a moveable bone on the front of the knee. It is wrapped inside a tendon that connects the large muscles on the front of the thigh (the quadriceps muscles) to the tibia. The back of the patella is covered with articular cartilage. The patella glides within a groove on the front of the femur.
The most common reasons for knee revision arthroplasty are
The functioning of a replaced knee depends on its fixation to the bone. A proper cementation of the implant onto the bone is necessary for fixation. Non-cemented ( biological ) fixation is also available now with good long term results.
Though, implants are firmly fixed at the initial knee replacement surgery, they may become loose over a period of time. Friction caused by the joint surfaces rubbing against each other wears away the surfaces of the implant, creating tiny particles that accumulate around the joint. In a process called aseptic (non-infected) loosening, the bond of the implant to the bone is destroyed by the body’s attempt to digest the wear particles. During this process, normal bone is also digested. This condition is known as osteolysis, which can weaken or even fracture the bone.
When the prosthesis becomes loose, the patient experiences pain, change in alignment, or instability. Aseptic loosening is the most common mode of failure of knee implants.
While carrying out a total knee replacement, the large foreign metal and plastic implants may serve as an agent for the bacteria to enter into. If an artificial joint is infected, it may become stiff and painful. Though, the implants remain well fixed, the pain, swelling and discharge from the wound make the revision surgery necessary. However, due to the advanced surgical techniques and innovative antibiotics, the risk of infection remains less than 1%.
If the degree of infection and damage is comparatively low, a simple washout of the knee with component retention is enough. Otherwise, a complete replacement of all the implants may be required.
In an infected knee replacement, two separate surgeries are required. Firstly to remove the old prosthesis and insert a block of cement with antibiotics (antibiotic-impregnated cement spacer). The second surgery is to remove the spacer and insert new prosthesis. Intravenous antibiotics are given during this period to eradicate the infection.
Fracture can happen near an artificial joint. The type and extent of the fracture determines the requirement of revision . Normally, fractures around the knee implants (Periprosthetic fractures ) that disrupt the fixation or the stability of the implant may require revision surgery.
A revision is also required when the artificial joint dislocates. When happens, it is very painful. However, it is rare that a knee joint completely dislocates. It can happen when the knee joint it too tight or too loose. If the knee joint is loose, it can cause unsteadiness and pain and if it is too tight, the knee is usually painful and does not have good range of the motion.
Patient- level- Factors: Factors such as age , activity level, surgical history, and weight can contribute to implant failure. If the patient is young and more active, the rate of revision is higher compared to older and less active patient. Obese patients have a higher incidence of wear and loosening. Patients with previous knee surgeries are at higher risk for infection and implant failure.
Before the revision surgery, many possible complications have to be addressed. Your surgeon will discuss all these with you. Be sure to ask about all your apprehensions like your recovery, the risks associated with it and the parts of the procedure, Your surgeon will have to plan carefully for the revision operation.
Once you decided to go ahead with surgery, several things may need to be done. To ensure that you are in the best possible condition to undergo the operation, your orthopedic surgeon will ask for a complete physical examination. He may consult with your family doctor as well before the surgery.
To check for loosening of artificial joint, doctors may suggest for a bone scan. When an artificial joint is loose, the bone around the joint reacts by trying to form new bone, a process called remodelling.
The bone scan is done by injecting you with a low-dose radioactive chemical. Hours after, a large sophisticated camera is used to take a picture of the bone around the artificial joint. The picture will show whether artificial joint is loose and there is remodelling going on, The picture also shows a spot where the chemical has been added to the newly forming bone. The brighter the hot spot, the more likely the artificial joint is loose.
If the doctors have the opinion that artificial knee is loose, other medical tests will carry out to find out the reason for the same. Before any plans are made to revise the artificial joint, orthopedic surgeons want to make sure that the knee is not loose because of infection.
To check for infection, blood tests may be required. Your surgeon may also need to aspirate your knee, by inserting a needle into your knee joint, removing fluid, and sending the contents to the laboratory. Replacing any artificial joint that is infected is much demanding than replacing a non-infected, loose artificial joint. Sometimes, infection makes a revision impossible.
Skin problems are common for people having knee revision arthroplasty. People with low level lymphocytes (white blood cells that form antibodies to fight off infection) have greater risk of incision problems. Your surgeon may ask for a blood count before surgery to make sure you have adequate numbers of lymphocytes.
Past incisions in the knee can further complicate the planned revision procedure. People needing a knee revision will have at least one previous knee incision. Most surgeons who do knee revision surgery prefer to make an incision that runs down the center of the knee.
This may not be possible due to previous knee incisions. The second choice is usually toward the outer (lateral) side of the knee(Lateral is the side furthest from your other knee). If the skin appears to be too tight for a planned incision to close, the risk of wound complications is high after the revision procedure. The orthopedic surgeon may need to consult with a plastic surgeon to ensure the best approach and result.
Another option is to use soft-tissue expanders. These are placed just under the skin next to where the revision incision will eventually go. The expanders stay in for up to eight weeks and are removed when you go in for the revision surgery. The idea is that the skin will have stretched enough so that, when the revision procedure is done, the edges of the skin can be closed and sutured together.
Before surgery, you may also need to spend time with the physical therapist who will manage your rehabilitation after the surgery. The therapist begins the teaching process before surgery to ensure that you are ready for rehabilitation afterwards. One purpose of the preoperative therapy visit is to record a baseline of information. This includes measurements of your current pain levels, functional abilities, and the available movement and strength of each knee. Any swelling in the artificial knee is noted.
A second purpose of the preoperative therapy visit is to prepare you for your upcoming surgery. You will begin to practice some of the exercises you will use just after surgery. You will also be trained in the use of either a walker or crutches. Finally, an assessment will be made of any needs you will have at home once you’re released from the hospital.
You may be asked to donate some of your own blood before the operation. This blood can be donated three to five weeks earlier. Your body will make new blood cells to replace the loss. If you need a blood transfusion during the operation, you will receive your own blood back from the blood bank.