Your knees work hard during your daily routine, and arthritis of the knee or a knee injury can make it hard for you to perform normal tasks. If your injury or arthritis is severe, you may begin to experience pain when you’re sitting down or trying to sleep.

Sometimes a total knee replacement is the only option for reducing pain and restoring a normal activity level. If you and your doctor decide a total knee replacement is right for you, the following information will give you an understanding of what to expect.

A total knee replacement involves cutting away the damaged bone of the knee joint and replacing it with a prosthesis.  This "new joint" prevents the bones from rubbing together and provides a smooth knee joint.

Implant Components        

In the total knee replacement procedure, each prosthesis is made up of four parts. The tibial component has two elements and replaces the top of the shin bone or tibia. This prosthesis is made up of a metal tray attached directly to the bone and a plastic spacer that provides the bearing surface. The femoral component replaces the bottom of the thigh bone or femur. This component also replaces the groove where the patella, or kneecap, sits.

The patellar component replaces the surface of the patellar button, which rubs against the femur. The patella protects the joint, and the resurfaced patellar button will slide smoothly on the front of the joint.

The Procedure

Before you are taken to the operating room you’ll be given medication to help you relax, and the anesthesiologist will talk with you about the medications he will be using.

Once you are "under" the surgeon will begin by making an incision in your leg to allow access to the knee joint.  He’ll then expose the joint and place a cutting jig or template on the end of the femur, or thigh bone. This jig allows the surgeon to cut the bone precisely so that the prosthesis fits exactly. Once the femur is cut, the tibia is cut using another jig for proper alignment of the knee prosthesis. The undersurface of the patella is then removed.

Now it’s time to place the prosthesis. This begins with the femoral prosthesis, which is cemented in place using a special bone cement. Next the metal tray is attached to the top of the tibia. This will provide the weight-bearing surface of the femur. The plastic spacer is then attached to the metal tray. This will provide the weight-bearing surface of the femur. If this component should wear out while the rest of the artificial knee is sound, it can be replaced. This is known as a "revision." Next the patellar button is cemented in place behind the knee cap. Finally, the incision is closed, a drain is put in, and the post-operative bandaging is applied.

Returning Home

You will be discharged when you can get out of bed on your own and walk with a walker or crutches, walk up and down three steps, bend your knee 90 degrees and straighten your knee.

At home you should begin ambulation with a cane as tolerated.  Keep your incision clean and dry and watch closely for any signs of infection.

You’ll continue your home exercise program and go to outpatient physical therapy, where you will work on an advanced strengthening program and such programs as stationary cycling, walking, and aquatic therapy.

Your long-term rehabilitation goals are a range of motion from 100-120 degrees of knee flexion, mild or no pain with walking or other functional activities, and independence in all activities of daily living.

Computer Assisted Surgery (CAS)  Knee Replacement

Total knee replacement surgery isn’t new. It has been practiced worldwide for 40 years, and as might be imagined, the procedure has been refined to the point where hundreds of thousands of people every year are returning to a life of pain-free mobility.

However, standard knee replacement surgery has its limitations -- the laws of physics being chief among them. A surgeon must implant the orthopedic device in such a manner that its components-a metal and plastic platform atop the tibia and a metal surface on the bottom of the femur-rub together, or "articulate," at precise angles in order to prevent premature or excessive wear of the implant.

If, during the procedure, a surgeon shaves off bone at an angle just five degrees from perfection, the uneven wear and tear during normal physical activity literally could shave years off the life expectancy of the device. That may lead to additional knee replacement surgeries during a patient’s lifetime.  As is commonly practiced today, a surgeon achieves proper alignment through "feel."  That is, he uses specialized cutting blocks combined with his years of operating room experience to determine where best to remove bone for the implant.  Once the cut is made, the natural bone cannot be replaced. Thus, a carpenter’s advice to "measure twice, cut once" is especially vital in knee replacement surgery.

The New Solution

Computer-assisted surgery addresses this issue of alignment with an advanced convergence of multiple medical technologies. Using infrared cameras, digitized bone images and simple tracking devices, Smith & Nephew’s computerassisted knee replacement procedure achieves alignment to within two degrees and two millimeters of total accuracy.

How It Works

The logic is simple:  By combining digital images of the femur and tibia with an implant-specific software package, the computer hardware can track the precise position of the patient’s leg, the implant and the surgeon’s instruments at all times during the procedure. It is as if the patient’s leg has a GPS tracking system the computer uses to follow it during surgery.

Do not fear -- the surgeon performs the surgery. The computer simply puts together all of the information coming in from the patient and the instruments and tells the surgeon where the precise cut should be made. Given that every patient's knee geometry is different, this level of patient-specific, computer-guided accuracy is unprecedented in the history of knee replacement surgery.

The Arrays

"Arrays" are metal prongs with small reflective spheres at their extremities. These devices attach to the surgical instruments and to the patient’s tibia and femur. Once they are fixed in place, their positions in space are tracked throughout the procedure. That way, the computer will know exactly where the instruments are in relation to the patient’s bones, based on where the spheres are at any given second.

The Camera

The camera emits infrared light that reflects off the spheres connected to the arrays. It collects this reflected infrared light, and sends the information about the location of the source of the reflection (the spheres on the arrays) to the computer.

The Computer

The computer receives information about where the spheres are in space, and combines that data with digital images of the patient’s anatomy and three-dimensional virtual images of the orthopaedic implants and surgical instruments.

The Software

The software displays on the screen the virtual images of the instruments, implants and bones and guides the surgeon through each step of the procedure. The software alerts the surgeon when the instrument is in the most accurate position to make the ideal cut. Also, it guides the surgeon as he determines where to best place the knee implant against the bones.

Patient Benefits

As you might imagine, a surgeon armed with these tools has the potential to achieve better outcomes for the patient.  As the computer-assisted procedure evolves, it will become less and less invasive.

It has already eliminated the use of an intramedullary (IM) rod-a device inserted up the length of the femur used for determining proper knee implant alignment in relation to the hip joint. Since the data generated by the computer replaces this device, patients undergoing computer-assisted knee surgery may have a reduced risk of fat embolism, caused when the IM rod forces body fat into the patient’s blood stream. If fat travels through the blood stream, it could become lodged in the heart or brain and cause heart failure, dementia or stroke.

Further, the quality and accuracy of the virtual image provided to the surgeon by the computer enables smaller incisions while achieving the same successful outcomes.  Smaller incisions lead to faster surgeries, shorter hospital stays and shorter rehabilitation.

The benefits to the patient include:

*  The elimination of the IM rod reduces the risk of fat embolism.

*  The increased "vision" the procedure provides makes minimally invasive surgery possible. This means a shorter scar, less physical therapy and a faster return to your normal life.

*  The accurate alignment and placement of the implant may extend its lifespan and prevent future corrective surgeries.

*  Since the computer accurately assesses "joint laxity," or soft tissue balance, the surgeon may not need to disrupt as much soft tissue-such as muscle, ligaments and tendons-when determining how tightly the new implant fits in place. This also reduces rehabilitation time and returns you to your active lifestyle more quickly.

A total knee replacement involves cutting away the damaged bone of the knee joint and replacing it with a prosthesis.  You will be under anesthesia during the procedure.

After your surgery is completed, you will be transported to the recovery room for close observation of your vital signs, circulation, and sensation in your legs and feet. As soon as you awaken and your condition is stabilized, you will be transferred to your room.

When you wake up you will find a large dressing applied to your incision in order to maintain cleanliness and absorb any fluid. There may be a drain placed near your incision in order to record the amount of drainage being lost from the wound.

You may be wearing elastic hose, and/or a compression stocking sleeve designed to minimize the risks of blood clots.

Your doctor may prescribe a PCA (patient-controlled analgesia) that is connected to your IV. The unit is set to deliver a small, controlled flow of pain medication and is activated when you firmly press the button on your machine. Press the button anytime you are having pain.

You may have a catheter inserted into your bladder as the side effects of anesthesia may make it difficult to urinate.

A continuous passive motion (CPM) unit may be placed on your leg to slowly and gently bend and straighten your knee.  This device is important for quickly regaining your knee range of motion. When your leg is not in the CPM, you may be wearing a knee immobilizer to protect your knee when you come to standing.

Total Knee Replacement Rehabilitation

Knee replacement surgery is a complex procedure, and physical knee rehabilitation is crucial to a full recovery. In order for you to meet the goals of total knee surgery, you must take ownership of the rehabilitation process and work diligently on your own, as well as with your physical therapist, to achieve optimal clinical and functional results.  The knee rehabilitation process following total knee replacement surgery can be quite painful at times.

Early Rehabilitation

Your knee rehabilitation program begins in the hospital after surgery. Early goals of knee rehabilitation in the hospital are to reduce knee stiffness and maximize post-operative range of motion as well as to help you get ready for discharge.

The following steps may be taken to help maximize your range of motion following surgery.

*  Strict adherence to the CPM protocol as prescribed by your surgeon

*  Early physical therapy (day 1 or 2) to begin range of motion exercises and walking program

*  Edema control to reduce swelling (ice, compression stocking, and elevation)

*  Adequate pain control so you can tolerate the rehabilitation regimen

Outpatient Physical Therapy

Your outpatient knee rehabilitation program will consist of a variety of exercises designed to help you regain range of motion in the knee and build strength in the muscles which support the knee. You will follow an advanced strengthening program, adding weights as tolerated. A stationery cycle and walking program will be used to help increase range of motion and stamina, and an aquatic therapy program may be added as well.

For more info, visit the Smith & Nephew website:

http://global.smith-nephew.com/us/patients/knee_replacement_12822.htm

©2003 Smith & Nephew, Inc.    Used with permission.