Knee Replacement

Knee replacement is a procedure frequently carried out for the treatment of knee arthritis. It is a major orthopaedic operation carried out in many hospitals in the developed world.
Decisions regarding whether and when to undergo knee replacement surgery are not easy. As a patient you should understand the risks as well as the benefits before making these decisions. Your GP, physiotherapist and surgeon will be helpful in assisting you in making the decision.
Most patients arrive on the day of surgery and stay in hospital for between 3 and 7 days. The time spent in hospital is to: control your pain; to ensure that no early complications of surgery have developed and also to start working with the physiotherapists to make an early return to walking.

Activity before surgery
Keep as fit as possible!

Maximising the function of the worn knee before surgery by improving the muscles gives the patient an advantage when it comes to getting going again after the operation.

Walking, swimming and cycling are good for maintaining musculature. When swimming it is often best to avoid breast-stroke leg kicks due to the strain it places on the knee. Many patients also get significant benefit from Tai Chi or Pilates. Impact exercises (e.g. running, racquet sports) would not be advisable for the worn knee.

The Operation  
The operation is usually carried out under general anaesthetic or under an injection into the back (spinal anaesthetic) to make the lower half of the body numb.

An incision is made over the front of the knee. The knee-cap (patella) is moved to one side to access the joint.
The operation involves resurfacing the articulating surfaces of the knee joint.

The lower end of the femur (thigh bone) is shaped with the help of cutting guides to accommodate a metal "femoral component". The correct size and position of the implant must be chosen to get the best outcome.

There are many manufacturers of knee replacements and each design comes in a variety of sizes. Your surgeon will measure the size of your bones during the operation to use the best-fitting size for you but may also have planned what size would fit your knee best prior to surgery.

"Templating" the knee replacement to help choose the right size implant

A femoral component shown as it sits on the polyethylene tray

The top of the tibia (shin bone) is also cut and prepared to accommodate an implant. This is a flat metal tray that resurfaces the top of the tibia with a short stem inside the tibia to provide more stability to the component. Again, the position and size of the implant is very important for the best results.

A high density polyethylene tray sits between the 2 metal components. This may have a post on it to provide more stability to the knee (as shown in the picture). The alternative to this is for the surgeon to leave one of the ligaments (the posterior cruciate ligament) within the knee to help stabilise it.

For the tray with the post (a posterior stabilised design) the ligament is removed.

The polyethylene tray (with a post)

Many surgeons also replace the back of the knee-cap (patella) with a polyethylene implant. Some surgeons always do this and some do it only when they feel it is indicated.

In this x-ray the knee cap has not been replaced but sits well in the "trochlea groove"

Before cementing the components into the knee the surgeon confirms that the knee is"balanced". This means that the knee should be stable from side-to-side and front-to-back; not too "tight" and not too "loose"; the knee should bend and straighten nicely and the patella should run smoothly in the groove of the femoral component.
The knee is then closed with sutures and dressings applied. 

An x-ray of a knee replacement post-operatively

After the operation
Initially, you will have a bulky dressing around the knee. This will be removed the day after surgery in the majority of cases to allow you to get the knee moving in the early phases of recovery.  You may have a drain in your knee to evacuate any bleeding. Mr. Arbuthnot does not normally use a drain.

Pain Control
Proper pain management is important in early recovery. Although pain after surgery is quite variable and not entirely predictable, it can be controlled with medication. Taking pain-killers allows you to carry out the exercises that get your knee moving. A painful knee can become stiff.

Pain management may start before, but certainly during the operation when the anaesthetist gives you medication whilst you are asleep to reduce the knee pain.

Some surgeons and anaesthetists use local anaesthetic around and within the knee and around the nerves of the knee to reduce pain straight after the operation. When this wears off the knee can become quite sore. It is recommended to take sufficient painkillers in this early post-op period to ensure that you can start your knee moving.

The knee can remain painful for some months after the operation (although most knees are significantly better by about six weeks).

Studies of the results of knee replacement show that 40% of knees have some pain for some of the time after a replacement procedure as a long term issue. However, 90% of knee replacements give a significant improvement in knee pain levels.

Get out of bed as soon as safely possible!
Although you will probably want to rest after surgery, early mobilization is important. You will need to build up strength in your quadriceps muscles (the muscles that extend the knee) to develop control of your new joint and to get you up and walking as soon as possible. Early activity is important as it improves the early range of motion in the new knee and reduces the risks of problems such as deep venous thrombosis and pressure sores. The days of a routine stay after knee replacement being 2 weeks or more are over! Most surgeons aim to have their patients home by day 4 or 5 after the operation.

You will be recommended to take blood-thinning medication to help reduce the risk of blood clots from forming in the leg veins, but getting walking as soon as possible will also reduce this risk.

A physiotherapist will typically visit you on the day of your surgery and begin teaching you how to use your new knee.


Your hospital stay may last from 3 to 7 days, depending on how well you heal after surgery. Before you go home, you will need to meet several goals:

- Be safe moving around and up and down stairs
- Be able to bend your knee well
- Be able to straighten your knee

You may experience mild swelling in your leg after you are discharged. Elevating the leg and applying an ice pack for 10 minutes at a time will help reduce the swelling, particularly after you have been exercising it.

Wound Care
- Keep the wound area clean and dry. A dressing will be applied in the hospital and should be changed as necessary but normally not before 72 hours
- Do not shower or bathe until the sutures or staples are removed, usually 10 days after surgery. Again, the wound should be kept clean and dry.
- Notify your doctor if the wound appears red or begins to drain any fluid.
- Swelling is normal for the first 3 to 6 months after surgery. Elevate your leg slightly and apply ice to settle this down. A feeling of warmth in the knee can persist for up to 18 months!
- Calf pain, chest pain, or shortness of breath are signs of a possible blood clot. Notify your doctor immediately if you notice any of these symptoms.


Clot prevention
You will probably be given a blood thinning injection or pill to reduce the likelihood of clots forming in the veins of your calf and thigh. Not only could this be painful, but if a blood clot forms and then breaks free, it could travel in the veins to your lungs, resulting in a pulmonary embolism which can be very serious. It is generally advised to take this for 2 weeks after knee surgery (but up to 4 weeks for hip surgery). Check with your doctor.

Infection prevention
Because you have an artificial joint, it is especially important to prevent any bacterial infections from settling in your joint implant. Antibiotics are given around the time of surgery to minimise this risk. Before the surgery is carried out it is beneficial to ensure that all potential sources of infection are minimised: see a dentist if you have problems with your teeth; discuss in-growing toenails or other foot problems with a medical professional.

A slightly contentious issue is that of the risk of dental work for a person with a knee replacement: there is a possibility of dental surgery releasing bacteria into the circulation that can settle in a replaced joint. This can be a tragedy. Mr. Arbuthnot recommends taking "prophylactic" antibiotics if you are having dental surgery and have a replaced hip or knee. Also, if you develop an infection in the foot or leg below a joint replacement it is important to have this treated early to reduce the risk of "seeding" the infection into the replaced joint.

Pain control
Most people don't like to take pills. However, if you don't take enough pain-killers you won't do enough physiotherapy. It is very important to keep the knee pain post-operatively under control to allow you to get it moving. Your GP will be able to offer advice, but generally paracetamol, anti-inflammatories (such as diclofenac or ibuprofen) and opioid medication(such as codeine)  can be taken together to combine to settle the pain and allow exercise. For some patients, this combination will have to be altered and you should check with your doctor as to what is best for you individually.

Getting back to normal
Once home, you should continue to stay active. However, DON'T OVERDO IT!
You will have good and bad days but things should gradually improve on the whole. By 2-3 months things should be much easier.  The following guidelines are generally applicable, but the final answer on each of these issues should come from your surgeon, GP or physiotherapist.

Continue to do the exercises prescribed for at least two months after surgery. Riding a stationary bicycle can help maintain muscle tone and keep your knee flexible. Do not do too much too soon. The knee can become swollen if you do too much exercise due to "synovitis" or inflammation of the inside of the joint. If this happens use intermittent ice and rest to control it.

Try to achieve the maximum degree of bending and extension as soon as possible.

Sexual Activity
Can be safely resumed at 4 to 6 weeks after surgery.

If your right knee was replaced, avoid driving for 6 to 8 weeks. If your left knee was replaced and you have an automatic car, you may be able to begin driving at 1 to 2 weeks, provided you aren't taking strong medication. In either case your physiotherapist will be able to help advise you as to your fitness to drive.

Airport Metal Detectors
Some knee and hip implants occasionally set off detectors. Normally airport security are happy to scan the "offending limb" with a hand held detector and no problems ensue. If you want to be extra safe, ask you surgeon or GP for a letter stating that you have a joint replacement.

Return to Work
This depends very much on what you do. Ask your surgeon or physiotherapist

Other Activities - the American Academy of Orthopaedic Surgeons suggest the following as a level of risk.

DANGEROUS: running, contact sports, jumping sports, high impact aerobics

ACTIVITIES EXCEEDING USUAL RECOMMENDATIONS: repetitive lifting exceeding 50lbs, skiing, singles tennis

SAFE ACTIVITIES: walking, swimming, light hiking, golf, driving, dancing, recreational cycling

For specific other activities, ask your surgeon.



- Numbness at the front of the knee - it is common to have some numb areas over the front of the knee.
- Ongoing pain - 10% of knee replacements have "severe pain" some or all of the time post-operatively; 40% of replaced knees have "some pain" as a long term post-op issue. This continues to settle up until 18 months to 2 years after the surgery. The pain may be related to a problem with the knee replacement or it may be difficult to be sure where the pain is coming from

Passage of urine
can be difficult in the immediate postoperative period, and this condition can be aggravated if you have pre-existing prostate problems (men). A catheter may have to be used as a short term treatment.

Deep venous thrombosis (clot in the calf) - a small clot in the veins can develop in2-3% of patients having a knee replacement. This is higher if no preventative treatment is given.

Infection: affects about 2% of knee replacements - this can be disastrous and care should be taken at all stages to minimise risk. The treatment of infection is often major surgery.

Bleeding: approximately 10% of patients need a blood transfusion after knee replacement

Fracture - during the operation or afterwards

- Nerve injury - causing temporary or permanent numbness and/or weakness of the foot and leg
- Stiffness
- Damage to the artery at the back of the knee
- Pulmonary embolus (clot in the lungs)

Reasons for failure of a knee replacement

Knee replacements do have a finite life expectancy but should survive 20 years or more for the majority of patients. Early failure of the implant is a problem for a small percentage of patients however. Some reasons for failure are listed below.

- Improperly positioned components leading to early wear and sub-optimal function
- Loosening of the components
- Wear of the components
- Advancing wear and tear changes in the remaining compartments of the knee (i.e. the patella (knee cap) if it was not replaced at the initial operation)
- Instability of the knee
- Ligament injury
- Infection