The knee is a complex hinged joint. It is lined by articular cartilage, filled with joint fluid contained within its joint capsule. There are many diseases which may affect the knee joint but the most common is osteoarthritis. The simplest way to understand this process is that the joint has “worn out” through usage and that the articular cartilage has gone causing bone to move (articulate) on bone which can be painful. There are three compartments to a knee, medial (inner), lateral (outer) and patellofemoral (knee cap and the groove it moves in), which can be affected by arthritis. Some patients have isolated compartmental disease, but more commonly all three are involved.
Why is knee replacement surgery necessary?
Knee replacement surgery is only considered when all other alternative therapies are exhausted or no other alternative options are possible. Typically patients consider having a knee replacement when the arthritis in their knee becomes intrusive in their lifestyle. They complain of pain on walking which may limit their activity or walking distance. A significant proportion of patients complain of pain that wakes them at night. As the osteoarthritis progresses the knee becomes stiffer limiting flexion and extension and patients may develop progressive alignment abnormalities of the limb.
What does knee replacement surgery involve?
Knee replacement surgery involves replacing the damaged or diseased knee with an artificial joint.
For a knee replacement to be performed the patient will require an anaesthetic. Most patients where possible have a spinal injection to numb the legs temporarily – this is great for immediate post operative pain relief. Sedation or a general anaesthetic is usually also given.
There will be a scar over the front of the knee. Smaller scars are used for partial knee replacements. Initially you will be relieved of your arthritis pain but have surgical pain around and deep inside the scar. The knee will also swell and initially the knee is quite painful following surgery. This pain will gradually decrease, quickly at first with slower changes seen up to a year following surgery.
Antibiotics are given prior to surgery and for 24 hours afterwards to help prevent infection of the implant.
Some patients will have a urinary catheter inserted after the anaesthetic. This helps nursing and toilet care in the first 24 hours before the patient is fully mobile.
Different types of knee replacement are available. A total knee replacement is a procedure where every articular surface of the knee joint is replaced including the patella. A partial knee replacement would replace one compartment of the knee typically the medial (inner) compartment. The type of knee replacement offered is based on the patient’s wear pattern assessed both clinically and radiographically.
Total knee replacement is a successful operation for removing pain from an arthritic knee joint in the majority of patients. The diseased bone is removed and replaced with a metal implant on the end of the femur (thigh bone) and top end of the tibia (shin bone). Between the two, a polyethylene (plastic) insert is fixed to the tibial component and articulates (moves) with the femoral component. The patella (kneecap) has its articular surface removed and replaced with a polyethylene button. All components are fixed to the bone using special bone cement.
Recent advances have allowed patient specific knee replacement surgery to be performed. A MRI scan of the patients knee and an alignment x-ray are utilised to make cutting blocks. The blocks allow for accurate cutting of the patients bone. The final knee replacement is constructed using standard implants.
This surgery involves only one side of the knee joint being replaced. By definition it is a smaller operation which uses smaller incisions, and less bone is removed as only one part of the joint is operated on. The components used are also metal on both the femoral and tibial side fixed to the patient with bone cement, with a polyethylene insert sandwiched between the two. Typically patients require a shorter hospital stay and the recovery period is potentially quicker.
The Recovery Process
After the knee replacement the patient will be able to walk on the knee the next day, or that evening – if you recover quickly from the anaesthetic.
After the operation you will need walking aids, such as walking sticks, for the first four to six weeks. Many patients discard them before their first follow-up appointment at six weeks.
It is often recommended that you undertake physiotherapy to help you regain and improve the use of your new knee joint. The physiotherapy team will work on straightening and bending the knee and muscle strengthening. However, the best medicine is too use the new knee by walking as much as possible.
Two weeks after surgery two sutures and paper stitches are removed. This is an easy and painless procedure.
An anticoagulant will be prescribed for 14 days following the surgery to help decrease the risk of a deep vein thrombosis (Blood clot in the leg veins). During the inpatient stay mechanical foot pumps will also be employed to help decrease this risk. Patients will wear ted stockings for six weeks following the operation.
Some patient’s experience swelling and bruising of the leg after undergoing knee replacement surgery. This is normal. If you experience painful or worrying swelling a scan maybe required to rule out a deep vein thrombosis.
The majority of people can resume normal activities within two to three months but it can take up to a year until you experience the full benefits of your new knee.
Driving is allowed after the six week check up, if all is proceeding normally.