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.

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. 

                                              
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.  

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.

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.

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.

If you have further questions, please use the ‘contact and feedback' link to tell me about your query, and I will be delighted to respond to any comments, questions or concerns.