Frequently Asked Questions
This page provides a brief introduction to knee replacement. It can help you make a list of questions to ask your doctor, but it is not meant to provide complete information. Check with your surgeon's office about more comprehensive resources and patient education materials.
What causes knee pain?
There are many different causes of knee pain, including injury, arthritis and infection.
Is there a cure?
It depends on the problem. Some knee pain can be treated through rehabilitation, other cases may require surgery.
What is a knee replacement?
In total knee replacement surgery, the parts of the bones that rub together are resurfaced with metal and plastic implants. Using special, precision instruments, your surgeon will typically remove the damaged surfaces of all three bones. The replacement surfaces will then be fixed into place.
The surface of the femur is replaced with a rounded metal component that comes very close to matching the curve of your natural bone. The surface of the tibia is replaced with a smooth plastic component. This flat metal component holds a smooth plastic piece made of ultra-high-molecular-weight polyethylene plastic that serves as the cartilage. The undersurface of the kneecap may also be replaced with an implant made of the same polyethylene plastic.
How do I know if I need a knee replacement?
If you have difficulty walking or performing everyday activities such as
getting dressed, it may be time to consider knee replacement surgery.
Doctors generally try to delay total knee replacement for as long as possible in favor of less invasive treatments. However for patients with advanced joint disease, knee replacement offers the chance for relief from pain and a return to normal activities.
How do I prepare for knee replacement surgery?
If you and your surgeon decide that total knee replacement is right for you, a date will be scheduled for your surgery. Several things may be necessary to prepare for surgery. For example, your surgeon might ask you to have a physical examination by an internist or your regular doctor.
Because blood transfusions are likely to be needed during your surgery, you may want to donate one unit of your own blood, or possibly two units if your surgeon feels it is needed. All preparations for surgery should be discussed with your surgeon.
What happens during knee replacement surgery?
On the day of surgery, a small tube (intravenous line) will be inserted into your arm. This tube will be used to administer antibiotics and other medication during your surgery. You will then be taken to the operating room and given anesthesia. After the anesthesia takes effect, your knee will be scrubbed and sterilized with a special solution.
The surgery will begin with an incision over the knee that will expose the joint. When the bones are fully visible to the surgeon, special, precision guides and instruments are used to remove the damaged surfaces and shape the ends of the bones to accept the implants.
The implants are then secured to the bones. It might also be necessary to adjust the ligaments that surround the knee in order to achieve the best possible knee function. When the surgeon is satisfied with the fit and function of the implants, the incision will be closed.
A special drain may be inserted into the wound to drain the fluids that naturally develop at the surgical site. A sterile bandage will then be applied, and you will be taken to the recovery room, where you will be closely monitored. Your surgery will likely take between one and three hours, depending on your individual circumstances.
As your anesthesia wears off, you will slowly regain consciousness. A nurse will be with you, and may encourage you to cough or breath deeply to help clear your lungs. You will also be given pain medication. When you are fully awake, you will be taken to your hospital room. Your knee will remain swollen and tender for a few days.
How is the implant affixed in the body?
Generally, implant systems are affixed to the body in one of three ways:
1. Cemented with bone cement
2. Cementless (biologic ingrowth)
3. Combination of 1 & 2
A special type of acrylic bone cement may be used to secure some or all of the implant components to the bone. If used, the bone cement takes about 15 minutes to set.
In other cases, the implants may be implanted into the bone without cement. These components have a special porous coating that allows tissue to grow into it for fixation.
In some cases, your surgeon may choose a combination of cement and cementless attachment, depending upon the implant components and the condition of the bone around the knee joint.
The decision as to whether to use a cemented or cementless component depends upon many factors, including the intended use of the product, surgeon philosophy and the patient’s condition.
What can I expect after knee replacement surgery?
When you are back in your hospital room, you will begin a rehabilitation program that will help you regain strength, balance, and range of movement in your knee. This program will be designed specifically for you. It may include a machine, called a continuous passive motion machine that automatically moves your leg to help reduce stiffness.
Your physical therapist will help you perform appropriate exercises. About 24 hours after surgery, you will probably be asked to stand. Within the next 24 hours, you will probably begin to walk a few steps with the help of a walker. You will be discharged as soon as your surgeon determined that you have recovered sufficiently. You can expect to stay in the hospital for about three days after your surgery. You may or may not be transferred to a rehabilitation facility for a few more days, as determined by your surgeon. Your bandages and sutures will usually be removed before you leave the hospital. At home, you will need to continue your exercises. Your physical therapist will instruct you about proper home care, and may continue to work with you.
How soon can I return to normal activities after surgery?
Within six weeks after surgery, most patients are able to walk with a cane. You will probably feel well enough to drive a car within seven to eight weeks after surgery.
In most cases, successful joint replacement surgery will relieve your pain and stiffness, and allow you to resume many of your normal daily activities. But even after you have fully recovered from your surgery, you will still have some restrictions. Normal daily activities do not include contact sports or activities that put excessive strain on your joints. Although your artificial joint can be replaced, a second implant is seldom as effective as the first.
Will an implant set off a metal detector?
Since knee implants are made of metal, there’s a chance they could set off metal detectors.
Patients have reported mixed experiences at airports: some detectors go off
and some don’t.
You may be provided with a special card to keep in your wallet explaining that you have a knee implant.
How common is knee replacement surgery?
Knee replacement is a routine surgery performed on over 600,000 people worldwide each year. Over 90% of people who have had Total Knee Replacement experience an improvement in knee pain and function.
How old is the average patient?
In the U.S., the average joint replacement patient is around 65-70 years old, however patients of all ages have received knee implants.
What about sex?
Doctors generally allow patients to resume sexual activities as soon as they feel able. In the months following surgery, patients are generally advised to take it easy and modify their positioning to keep pressure off of the joint while it’s healing. As always, it is best to consult with your doctor about what’s safe for your particular condition.
I am knock-kneed/bow-legged. Can knee replacement surgery correct this?
Many people are born with a natural tendency toward knock knees or
bowleggedness. However, severe arthritis can lead to an uncomfortable degree
One of the goals of total knee replacement is to restore your body’s natural alignment. Zimmer has special instrumentation to help surgeons replicate natural, optimum alignment.
How long will a joint replacement last?
Longevity of the prosthetic knee varies from patient to patient. It depends on many factors, such as a patient's physical condition, activity level, and weight, as well as the accuracy of implant placement during surgery. It is useful to keep in mind that prosthetic joints are not as strong or durable as a natural, healthy joint, and there is no guarantee that a prosthetic joint will last the rest of a patient's life.
Today, total knee replacement has become a common and predictable procedure. Many patients enjoy relief from pain and improved function, compared to their status before surgery. As a result, some patients may have unrealistic expectations about what the prosthetic knee can do and how much activity it can withstand. As with any mechanical joint, the knee components move against each other. Natural fluid in the joint space, called synovial fluid, helps to lubricate the implants just as it lubricates the bones and cartilage in a natural joint. Still, the prosthetic components do wear as they roll and slide against each other during movement. As with car tires or brake pads, the rate of wear depends partly on how the knee joint is used. Activities that place a lot of stress on the joint implants, as may be the case with heavier and more active patients, may reduce the service life of the prosthesis. Implant loosening and wear on the plastic portions of the implant can lead to the necessity for revision surgery to replace the worn components, or all of the components. Your doctor will be in the best position to discuss these issues with you, taking into account your particular clinical circumstances, the type of implants used, and your post-surgical lifestyle.
Talk with your doctor about the following points, and how they might affect the longevity and success of your knee replacement:
- Avoiding repetitive heavy lifting
- Avoiding excessive stair climbing
- Maintaining appropriate weight
- Staying healthy and active
- Avoiding "impact loading" sports such as jogging, downhill skiing and high impact aerobics
- Consulting your surgeon before beginning any new sport or activity
- Thinking before you move
- Avoiding any physical activities involving quick stop-start motion, twisting or impact stresses
- Avoiding excessive bending when weight bearing, like climbing steep stairs
- Not lifting or pushing heavy objects
- Not kneeling
- Avoiding low seating surfaces and chairs