When a knee replacement is performed and the rehabilitation has been completed, more than 90% of patients will rate their outcome as good or excellent. However, not everyone has a pain-free knee after the procedure. Moreover, all forms of knee replacement surgery have a finite lifespan, gradually with time the replaced knee starts wearing out, a person may suffer from pain stiffness and difficulty in day to day activity. This is when you need further surgery, this is called Revision knee replacement.
A knee revision surgery is a complex surgical procedure usually preferred when there is major bone damage. Revision surgery requires preoperative planning and skilled surgeons. These knee replacement usually feature a longer stem which allows the component to be more securely fix into the bone cavity.
What causes knee replacements to wear out?
There are many reasons why a knee replacement may wear out or ‘fail’. The most common reason are:
- Loosening: It is wearing out of the plastic (polyethylene wear) which can often produce loosening of the implant from the bone (aseptic loosening) or sometimes cysts within the bone (osteolysis). Sometimes knee replacements loosen from bone without the polyethylene wearing out. Cemented implants can become loose because the cement-bone interface has failed. This is usually due to bone die back, meaning the tiny projections of bone that the cement initially attaches to having either broken off in weight bearing or simply deteriorated due to infection or weak bone (osteoporosis). Non-cemented implants can loosen for much the same reason except it is the implant-bone interface that fails. However, current state-of-the-art materials and techniques have improved the quality of implant fixation to the bone which had historically been a weak link that created a potential site of failure.
- Wear: Wear, usually by friction created among joints and implants made up of plastic and metal. Modern plastics used presently are quite durable, but still with time these plastic parts wear out with day to day use because they are softer than accompanying metal, there can never be a perfect (natural) alignment of this plastic and metal together, which causes friction and creates a few worn-off particles which can cause problems in nearby tissues as microscopic fragments get absorbed into the cells and create inflammatory conditions causing pain.
- Infection: Infection usually arises due to a substance called bio-film on the implant devices. It’s an organic material having a microscopic layer of inactive fungal material. Infection arises when the microbes become active and multiply. Infection is also caused when wear off particles comes in contact of cells in the surrounding area.
- Fractures: When treated individuals tend to put lower demands on their implants, knee becomes unstable and stiff which leads to dislocation or minor fractures of the knee,
- Instability: This means the knee is not stable and may be giving way or not feel safe when you walk.
- Osteolysis: This can occur due friction between implant and bone. When bone is being destroyed as a wear-off particles, leading to bone-loss. Very rarely knee replacements need to be revised on multiple occasions in order to correct the underlying problem. In the case of infection, two or more operations are often required to attempt a successful eradication of the infection.
How revision is different from replacement
A knee revision surgery is a complex surgical procedure where your surgeon removes the original implants, usually preferred when there is major bone damage. The surgery may also take longer to perform than an initial knee replacement. Revision knee replacement usually does not provide the same expected lifespan as an initial replacement. Surgical trauma, scar tissue, and mechanical weakening of components tend to reduce performance of a revised implant.
Recovery and outcomes
Care after knee revision surgery is similar to the care you’d take after total knee replacement. This includes both a light physical therapy and pain medications. A walker or crutches will be used early in the recovery period, gradually you will progress to walk without any assistance. Although pain relief and increased stability are expected outcomes, complete pain relief and restoration of function is not always possible.
Risks and Complications
As with any major surgery, there are potential risks involved. The decision to proceed with the surgery is made because the advantages of surgery outweigh the potential disadvantages. It is important that you are informed of these risks before the surgery takes place.
Complications can be medical (general) or local specific to the knee
Medical complications include: Allergic reactions to medications, blood loss requiring transfusion with its low risk of disease transmission, heart attacks, strokes, kidney failure, pneumonia, bladder infections, complications from nerve blocks such as infection or nerve damage, serious medical problems can lead to ongoing health concerns, prolonged hospitalization or rarely death.
Local complications include: Infection, blood Clots, fractures, stiffness, irritation, length inequality, dislocation, instability.