Total Knee Replacement
What is Knee Arthritis?
The bones in a normal knee are lined with a smooth layer of cartilage. This cartilage allows the adjacent surfaces in the knee to glide smoothly and painlessly against each other.
In the process of arthritis the cartilage is worn away (degenerates) with the end result of “bone rubbing on bone”. This process is painful and can result in inflammation of the knee joint. With progression of the disease the knee becomes increasingly painful, stiff and swollen, and may result in a deformity (bow legged or knock knee).
What is a Total Knee Replacement?
A total knee replacement is a prosthesis that is used to replace a knee joint that is affected by arthritis. It consistents of several components:
- An upper metal femoral component that is shaped and sized to fit to the contour of the end of the femur bone
- A metal tibial component which is flat and has a small stem attached to the undersurface of it. It sits on top of the tibia on the opposing side of the knee joint. Both metal femoral and tibial components are made of metal alloys, comprising of cobalt-chrome or titanium. They are both fixed to the bone with a special polymer called “bone cement”
- A plastic insert (“polyethylene insert”)which locks in to the tibial component sitting in it’s upper surface. The plastic liner is the bearing for which the femoral component moves against. The plastic is made of a special polymer call polyethylene which has been carefully manufactured to allow it last a long time with out wearing out. However, even with the latest manufacturing techniques, this still is similar to your articular cartilage in that it has a limited life span, and excessive forces are placed on it, it will wear out more quickly
- A patellar button which resurfaces the back of your knee cap. This is also made of polyethylene. It is not crucial that this is replaced all the time, and it is at the discretion of your surgeon on whether it is in your best interests to have this performed as well
When is a Total Knee Replacement helpful?
The most important reason for surgery is pain that is interfering with your quality of life and is not adequately controlled by other means (medication, injections, physiotherapy, activity modifications etc). This is a very individual decision and depends on your social requirements and activity demands.
What about minimally invasive surgery (MIS)?
Depending on the size of your knee, the degree of arthritis and deformity, and the amount of preoperative stiffness, you may be a candidate for MIS. This technique minimises surgical trauma to the quadriceps tendon and allows for faster recovery of strength, improved mobility in the first few weeks and sometimes less pain. Your surgeon will discuss this option with you during your initial consultation.
What happens on the day of your operation?
Undergoing a total knee replacement is a major operation. You will require specific tests (blood tests, ECG and other x-rays) and possible review by other specialists to ensure you are in optimal condition prior to your surgery. If you have a pre-existing condition (eg: heart disease or diabetes) you will need to be given the “all clear” by your treating physician before surgery.
Your anaesthetist will explain to you the various options with regards to anaesthetic during the operation and the anaesthetic most suitable for you. In addition, your anaesthetist will discuss the most effective post-operative pain relief for you.
What happens on the day of your operation?
You will be admitted to hospital usually the day of your surgery. Your surgeon will visit you to answer any other questions you may have regarding the surgery and also to mark the affected knee with an ink pen.
After your anaesthetic has been administered a tourniquet will be applied to your upper thigh and your leg will be painted with antiseptic solution. A routine draping will be performed with sterile sheets to allow exposure only of the knee.
A vertical incision is made on the front of your knee to allow access to the knee joint itself. The arthritic areas of your knee joint are removed and the bones are fashioned to allow placement of the knee prosthesis (comprising a metal femoral and tibial component) and straighten the leg as most people have some deformity (eg knock knees or bow legs). Bone cement is used to help stabilise the prosthesis to the bone. A plastic (polyethylene) insert is placed between the femoral and tibial components and acts as an articulating shock absorbing surface. The decision to resurface the patella (knee cap) will be dependant on its degree of arthritic involvement.
Before completion of the operation, the knee is checked for stability, alignment and degree of motion. Often, a small drain will be left in the knee for 24 hours after the surgery to remove unwanted blood from the knee. Dissolving stitches are used to close the wound, and the knee is then wrapped in a well-padded sterile bandage.
After your operation
You will wake up in the recovery ward where you will be closely monitored until you are ready to return to your ward. Here you will continue to be observed until you are fully awake.
You will spend the first post-operative day in bed. A physiotherapist will visit you to give you breathing exercises for your chest as well as exercises for your leg that can be performed whilst in bed. An x-ray of your knee will be taken the day after surgery to confirm optimal placement of the prosthesis.
Blood thinning medications will be administered daily to reduce the risk of blood clots (DVT) forming in your legs. In addition you will be given special stockings (TEDS) to wear on both of your legs. For the first 24 hours after the operation an inflatable sleeve will intermittently compress your calves to prevent stagnation of blood flow. You will receive intravenous antibiotics for 24 hours after the operation to decrease the risk of infection.
The dressings will be changed 48 hours after the operation. Your knee will be swollen and may have areas of bruising. This is normal. You will be under the daily supervision of a physiotherapist until you are discharged from hospital. The aims of these visits are to optimise motion in the knee, regain ambulation, improve muscle strength and control knee swelling (please refer to education booklet on Total Knee Replacement Rehabilitation).
Once you are mobilising safely, have regained appropriate motion in the knee and your pain is controlled by tablets you will be discharged home. Some patients require further in-patient care and are transferred to a rehabilitation unit.
What happens after you go home?
Your rehabilitation will continue after you leave hospital to initially maintain and then improve on what you have already achieved. This will take the form of a home exercise program and outpatient physiotherapy visits, which usually lasts 3-6 months.
An appointment will be made to see your surgeon at 6 weeks after your operation. The goals of your knee replacement surgery are to be walking independently, be able to bend your knee to 100-120 degrees and be pain free.