English version of the website of Dr. J.E.Perraudin, french orthopaedic surgeon in paris : : the content is intended for general information only and does not replace the need for personal advice from a qualified health professional.

Last updated Feb 12, 2017

Knee Replacement, knee prosthesis

Knee replacement is now a common procedure. It is used for arthritic knees when the patient gets too disabled by his symptoms (pain ++, deformity, loss of function) despite a good medical treatment. By resurfacing the damaged and worn surfaces of the knee can relieve pain, correct leg deformity and help resume normal activities. The longevity of the prosthesis is the main problem because it is difficult to predict.

There are different types of prosthesis (unicompartimental or total) but the overall design is similar : the damaged surface in the shinbone (tibia) is replaced by a metal plate and a carved sleeve of metal is placed over the lower end of the thigh bone (femur). The metal used is made of cobalt chrome alloy. These pieces of metal are fixed into position using a cement or, in some cases, pressed into position and the fixation occurs using a biological method. Between these two metal pieces, a high density polyethylene platform is inserted.

I use a mobile-bearing prosthesis .

  • In a mobile-bearing prosthesis, the femoral component and tibial tray move across a polyethylene insert to create a dual-surface articulation.. This helps reduce the amount of wear to the bearing and helps prevent loosening in places where the prosthesis attaches to bone. Mobile-bearing knees are also designed to allow greater rotation of the knee.
  • Advantages : it can reduce early wear failure. The insert's mobility ensures congruent contact between the femoral and tibial components and conformity or the surfaces that move together when you bend and rotate your knee during activity.
  • Disadvantages : they are less forgiving of imbalance in soft tissues (medial and lateral collateral ligaments). They may increase the chance of dislocation.

The kneecap : the worn out cartilage is removed along with a sliver of the underlying bone and is replaced by a cemented plastic button. The kneecap is said to have been resurfaced.

For my part, I always use ciment in unicompartimental replacement. In total replacement, I use an hybrid fixation with ciment for the tibia and the patella. The femur piece is "pressfit" without ciment.

Computer assistance is useful, particularly for difficult knees but it does not replace the experience of the surgeon!. I use it most of the time. For more details, you can have a look to my french website.

Successful results occur when patients are willing to endure quite a bit of uncomfortable stretching and exercise early in their recovery with the help of a physiotherapist. It requires a lot of determination to keep stretching a painful swollen recently operated knee but the effort is worthwhile.

Dental evaluation : although the incidence of infection after knee replacement is very low, an infection can occur if bacteria enter your bloodstream. Treatment of significant dental diseases (including tooth extractions and peridontal work) should be considered before your total knee replacement.

Urinary evaluation : a pre-operative urological evaluation is necessary for the same reasons (urinary infection or prostate disease).

You will be admitted to the hospital on the day before surgery.If needed, you will be evaluated by a member of the anesthesia team.

Post operatively:

You will be moved to the recovery room, where you will remain a few hours while your recovery from anesthesia is monitored.Your blood pressure, and heart rate will be monitored by a nurse, who, with the assistance of the doctor, will determine when you are ready to leave the recovery room. Then you will be taken either to your hospital room or to special room for 24 hours to continue monitoring if necessary.

Medication will be given to you to make you feel as comfortable as possible.Pain management is very important for you and for us.

You will have blood thinners to prevent blood clots.

Foot and ankle movement is encouraged immediately following surgery to increase blood flow in your leg muscles to help prevent leg swelling and blood clots. Most patients begin exercising their knee by tightening their thigh muscle immediately following surgery.

After 24 hours rest, the patient is able to get out of bed. He is helped walking as soon as the second day, either using a frame or crutches. He starts to bend his knee with the physiotherapist and with the help of a continuous passive motion (CPM) machine. This machine gently and steadily bends and straightens the knee. Over the following week, the patient increase his knee flexion and the amount he is able to walk on sticks. He will then try to walk up and down the stairs.

The inpatient stay is usually between 8 and 12 days. Physiotherapy is continued as an outpatient for a varying amount of time up to two months. To check on progress, I will see you again six weeks later or at anytime if necessary. You must keep me informed as you go along of every problem you may have: this is important to allow rapid diagnose and treatment of possible complications +++.

After surgery, you may either go back home (you will need help for several weeks with such tasks as cooking, shopping, bathing, and doing laundry) or go for a short stay in an extended-care facility during your recovery before going home.

Wound care : Staples running along your wound will be removed two to three weeks after surgery.Avoid soaking the wound in water until the wound has thoroughly sealed and dried.

Some loss of appetite is common for several weeks after surgery. A balanced diet is important to promote proper tissue healing and to restore muscle strength

After you return home

The exercises recommended are a crucial part of your recovery, so it is essential to continue to do them. An average of 115° of motion is generally anticipated after surgery. Your activity program should include

  • a graduated walking program to slowly increase your mobility in your home and later outside.
  • Resuming other normal household activities, such as sitting and standing and climbing stairs
  • Specific exercises several times a day to restore movement and strengthen your knee. You will do them by yourself and with a physical therapist who will come home three to five times a week.
  • When you are resting, you should rest with your leg raised to help prevent swelling of the leg and ankle.

Driving : You should not drive until you are confident that you could perform an emergency stop without discomfort.Most individuals resume driving approximately 4 to 8 weeks after surgery;

Depending on the type of work you do, you can usually return to work after two or three months.

Avoiding problems after surgery :

  • Avoid falls and injuries
  • For the first 2 years after your knee replacement, you must take preventive antibiotics before dental or surgical procedures that could allow bacteria to enter your bloodstream.
  • After 2 years, talk to your orthopaedist and your dentist or urologist to see if you still need preventive antibiotics before any scheduled procedures.
  • See your orthopaedic surgeon once a year,for a routine follow-up examination and x-rays.


A knee replacement is a commonly performed and generally safe surgical procedure. For most people, the benefits are far greater than the disadvantages.

However, in order to make an informed decision and give your consent, you need to be aware of the possible side-effects and the risk of complications.

Side effects : after surgery your knee will be sore when you move it and swollen for up to three months. You will have a scar in front of the knee. The scar and the outer side of the knee may be numb, which can sometimes be permanent.

Complications are when problems occur during or after the procedure. Most people are not affected. The main complications of any operation are bleeding during or soon after the procedure, infection and an abnormal reaction to the anaesthetic.

Some complications specific to a knee replacement :

  • A blood clot can develop in the veins of the leg (deep vein thrombosis, DVP). This clot can break off and cause a blockage in the lungs. It is usually treatable, but it can be a life-threatening condition.
  • The wound or the joint can get infected. Antibiotics are given during surgery to help prevent this.
  • Sometimes it is not possible to make the new knee fully stable and you may need to have another operation.
  • A build-up scar tissue occasionnally restricts movement. Another operation may be performed to break down the scar tissue. In rare cases, the loss of movement may be permanent.
  • The knee cap can become dislocated after surgery.

Docteur Jean Etienne Perraudin, last updated 1 Sept 2012

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