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02920 751 909
E mail:
cardiffhipandknee@gmail.com
Knee Replacements
Total knee replacement is one of the most successful treatment interventions in modern medical practice. In this operation, the surface of the knee joint is replaced with metal components and a polyethylene insert is interposed, which together form the artificial joint.
A large number of people have knee replacements and this page is
intended to help the reader understand knee replacement operations,
their advantages and disadvantages, and the
limitations.
The knee joint is a highly complex joint formed
between the lower end of the thigh bone (femur) and the top end of
the leg bone (tibia). The knee cap (patella) is located in front of
the knee and articulates with the femur.
The surface of femur and tibia, which form the knee joint, are lined with a smooth surface called the articular cartilage. Additionally, the knee has two crescent shaped cartilages called the menisci which are located between the femur and tibia and act as shock absorbers. There are four main ligaments in the knee – two cruciate and two collateral ligaments, which provide stability to the knee.
In arthritis, the articular cartilage becomes thin and wears out. This leads to knee stiffness, deformity and pain. Various conditions can affect the integrity of the articular cartilage. Most commonly, it is osteoarthritis (also called as osteoarthrosis), and other conditions include rheumatoid arthritis, arthritis following injury to the knee, and rarely tumours, rare inflammatory arthropathies, and infections.
Knee replacement is carried out to relieve pain from the degenerate joint.
Watch a video on knee replacement surgery
Click on the picture above
"Delighted with the knee operation - a fresh chance to enjoy things I always wanted to do"
- Linda Watkins, Cardiff
Primary or revision knee replacement
The first time the natural knee joint is
replaced is known as primary knee replacement. If further
operations are required to change one of both components, it is
called revision knee replacement.
In a primary knee replacement, the lower end of femur is prepared to accept a femoral component and the upper end of the leg bone is prepared to accept the tibial component.
The two components are fixed into bone either with special acrylic bone cement, or by cementless fixation. In cementless fixation, the size and shape of the prosthesis accurately matches the prepared bone and the metal joint is coated with a special surface which encourages bone ingrowth into the metal, hence providing a firm fixation and long term stability. This special surface coating may be Hydroxy-apatite, or porous coating. Cemented fixation is used more commonly than cementless fixation in knee replacements.
The knee cap can be changed at the same time if required, but this is not routine.
X rays showing arthritis of the knee. The space between the femur (thigh bone) and tibia (leg bone) is narrowed because of wearing of the joint surface.
X rays after total knee replacement. The ends of the bone have been replaced with metal components and there is a plastic in the middle
Computer
guided knee replacement
Computer
navigation is used in knee replacement to achieve accurate
placement of components. An infrared camera connected to
computer gives the surgeon detailed data about surgical resection
and soft tissue balancing. This information would not otherwise be
available to the surgeon using conventional techniques.
Additionally, it avoids insertion of alignment rods in the femur at
the time of the operation, and is believed to reduce risk of fat
embolism. The operating time is slightly longer with use of
caomputer navigation, and this is because of time taken to set up
and calibrate the computer. This technology is available in
Cardiff.
Personalised
knee replacement
A new
technique for doing knee replacement is by doing an MRI scan
(Magnetic resonance Imaging) prior to the operation. On the basis
of measurements in the scan, a special jig is prepared by the
implant company. This fits accurately on the bone at the time of
knee replacement and helps to achieve an accurate resection of
bone. As with computer navigation surgery, the actual
prosthesis used is the same as conventional technique. This
technology is available in Cardiff.
Gender specific knee
replacement
Bearing in mind the differences in anatomy and dimensions of men
and women knees, some knee replacements prosthesis have been
designed specifically for women. These are supposed to provide
a better fit, and hence better function. These special
implants are available in Cardiff.
Computer Navigation knee system Computer sceen which guides knee surgery Personalised knee replacement jig Persnolaised cutting blocks for knee surgery
Materials for knee joint
The knee joint prosthesis has a femoral component made of cobalt –
chrome. The tibial component is usually titanium or cobalt - chrome
and has a plastic fixed to it which is a (UHMWPE) plastic liner.
The patellar button is usually entirely made of UHMWPE and is
cemented into the knee cap. In the x ray picture above, the two
white parts seen on x rays in the artificial knee joint are the
metallic parts, and the clear space in between the two parts is the
plastic component.
The
operation
Knee replacement surgery is done under general
anaesthetic or spinal anaesthetic. Spinal anaesthetic is used more
commonly, as it is more comfortable for the patients and it helps
in postoperative pain relief as well.
The operation is done with patients lying flat on the back. The incision is around 15cm in length, and is placed vertically on the front of the knee. The surgery takes 60 to 80 minutes. A thin plastic tube (drain) collects any postoperative bleeding in a small plastic bag. This blood is reinfused back. The drain is removed on the day after surgery. Pain relief is provided by a PCA (patient controlled analgesia) pump, whereby patients can press a button to control the amount of pain killers injected, as per requirement. There is a safety mechanism to prevent overdose.
Normal diet is resumed the day after surgery. Usual hospital stay is between 3 and 5 days.
Mobilisation is started on the day following surgery. Initially a Zimmer frame is used to help mobility and this quickly progresses to crutches and then sticks. By 6 to 8 weeks, most people are able to mobilise well, and some may take up to 3 months to regain best mobility. The physiotherapists will help regain the movements and the muscle strength in the knee following surgery, and a range of exercises is advised to achieve a speedy recovery.
Risks of knee replacement surgery
Knee replacement is, by and large, a reliable
and successful surgery. However, a small number of people may have
problems following surgery. The success rate of surgery is 90 to
95% at 10 years.
The potential problems include –
1. Infection in the knee.
Infection in the replaced knee joint is a serious but rare problem and the risk is less than 1%. Superficial infections in the wound present as discharge from the wound, and generally respond to antibiotics and dressing. Deep infection presents as persistent wound discharge, formation of sinus over the wound, or persistent pain. Deep infection may often require revision knee surgery - removal of the artificial knee joint and insertion of a new joint.
The surgery is done in clean air operating theatres, and with use of appropriate antibiotics, along with antibiotic in the cement, the risk of infection is very low. Meticulous surgical technique and strict asepsis allows us to achieve an infection rate which is nearly zero. The infections encountered are generally blood borne infections from a remote site in the body - like the chest, or urinary tract.
2. Swelling and stiffness
Knee replacement is a major surgery and inevitably results in local swelling. This is usually temporary and settles in 3 to 6 months as knee movements are regained. Mild to moderate swelling in the knee after surgery is expected and is not a cause for concern.
Some patients experience stiffness and this gradually improves with progression of physiotherapy. It is important to do exercises to fully straighten the knee and to bend the knee.
Almost everyone will regain knee bending to a right angle and most will regain even more bending. The final range of knee bending after surgery is largely dictated by the range of movement prior to surgery. At the time of surgery, a lot of effort is made to maximise the range of movement.
About 1 % people may experience problems in bending their knee fully. In this situation a manipulation of the knee under general anaesthetic is needed to break the adhesions. Intense physiotherapy after manipulation helps to improve the range of motion.
3. Deep vein thrombosis and Pulmonary Embolism
Deep vein thrombosis is development of a blood clot in the veins of the calf, thigh or pelvis. This is a risk with any hip or knee surgery and prophylaxis against this provided in the form of oral tablets or by injections. Foot pumps are also used to physically help blood circulation. The duration of anticoagulant therapy is 2 weeks after operation.
Deep vein thrombosis causes swelling of the leg and pain, and temporarily delays rehabilitation following surgery. Clots require treatment with Warfarin.
Pulmonary Embolism is a very rare complication where a clot from the leg travels to the lungs and blocks circulation. Small clots are inconsequential and may not be noticed or detected. Large clots are potentially life threatening.
4. Ongoing pain in the knee
A small number of people (about 1%) may experience pain the knee after apparently successful surgery. This may be referred pain from the hip or spine, or it may be an undetectable deep infection. This requires investigations and sometimes further surgery may be needed to alleviate the pain.
5. Limp
Following knee surgery, walking aid in the form of Zimmer frame, crutches and sticks are needed temporarily. As muscle strength improves, the gait improves and by two months, most people are able to walk without sticks. Some people can take a longer time, and this is within normal expected recovery patterns.
6. Rare complications
Rare complications of knee surgery include chest infection, urinary tract infection, or injury to the nerves. Some people may require a urinary catheter for the first day or two after surgery, if there are preexisting problems of the urinary tract. The surgical incision of the knee is a vertical cut on the front of the knee. This results in unavoidable damage to some small nerves in the skin, which leads to numbness on the outer side of the knee adjoining the scar. This numbness may be permanent but is not a cause for concern.
In some instances, there may be a crack in the thigh or leg bone during fixation of the components. These are generally detectable and treatable at the same time.
The risk of dying as a result of knee replacement is extremely low – a fraction of 1%. Pulmonary embolus, heart attack or stroke, especially with a history of such an event in the past, are the underlying factors for this.
7. Long term complications
In the long term (years), the fixation of the artificial joint into the bone may become loose, or the polyethylene liner may wear out. These situations result in pain and damage to bone around the knee joint. Revision to a new knee joint is required to correct these problems.
Revision of the knee is more extensive operation than the primary surgery and the risk of complications is also higher in revision surgery.
Despite all the risks mentioned here, most patients (90%) have a speedy and uneventful recovery after knee surgery and do well. 5 to 8% may have a minor complication which delays rehabilitation, but does not affect the outcome. Only 1 or 2 percent end up with a significant problem. It is advisable that the surgery is undertaken only when the expected benefit outweighs the potential risks.
Care after surgery
Following knee replacement, driving is not
recommended for about 6 weeks. The insurance company should be
informed about the knee replacement surgery. An automatic
transmission car can be driven earlier after surgery to the left
knee.
Heavy work and lifting heavy objects is not recommended after knee replacement. Running and contact sport are also not recommended. Golf is possible, as is doubles tennis. Riding a bicycle is allowed after 2 to 3 months. Walking is not restricted after knee replacement. Gardening is limited and many people may experience difficulty in kneeling down and / or squatting. Kneeling and Squatting are allowed after knee replacement but almost half the patients may find this difficult.
If there was significant stiffness in the knee prior to surgery, it
may be difficult to regain further movement after surgery. This
means tying shoe laces and cutting toe nails may be difficult in
these situations.
These are broad guidelines and individual circumstances dictate
rehabilitation after total knee replacement.
Through meticulous technique, improved implants and high standard of care, the outcome following knee surgery is better than ever before.
I currently do over 200 hip and knee replacement operations
annually, and in my experience, among patients with knee
replacement surgery, infection rate is zero. Satisfaction rate is
95% and about 2% patients require redo operations at 4 year
followup.
These results have been possible through meticulous
technique and ensuring the joint is adequately balanced and
aligned. I have devised a new knee alignment device which wil
ensure more accurate knee balancing in future.
If you have further questions, please use
the ‘About me' link to tell me about your
query, and I will be delighted to respond to any comments,
questions or concerns.