Jeffrey M. Nakano, MD, Steve Heil, MD, Mark Luker, MD

Overview
Knee replacement surgeries, also known as knee arthroplasties, are one of the most life enhancing and successful medical interventions of the 20th century.  Modern techniques of this procedure date back to the 1960’s, and in 2016 more than 600,000 knee replacement will be performed in the United States alone.  Knee arthroplasties can be broadly classified as total knee replacements, where all the joint surfaces are replaced with artificial parts, or partial knee replacements, where only the damaged portions of the knee joint are replaced.

These procedures are performed for patients who, for one reason or another, have experience destruction of the knee joint surface.  The most common reason for this destruction is osteoarthritis, which is generally associated with the aging process, but may have genetic influences.  The predominant symptom is pain in the knee that is mainly associated with walking and standing, and the pain is generally better with sitting and lying down. The diagnosis of severe arthritis can usually be made with x-rays, but sometimes a MR scan will be helpful.

The usual reason to choose to have a knee replacement is the inability to perform the activities associated with daily life, such as walking, climbing stairs, and getting up and down from a seated position, after nonsurgical interventions such as medications, injections, physical therapy, use of braces or other external support have failed.  As with all mechanical devices, knee arthroplasty components will fail eventually, but it would not be unreasonable to expect the components to last 20 years or more.  When you think about it, we would all be satisfied if we had a car or refrigerator that lasted 20 years!  The present generation of knee replacement components will probably fail sooner if subjected to impact activities such as running.

Health Care Decisions to Consider Before the Surgery
Knee replacement surgery remains a major surgery, despite the fact that in some centers across the country total knee arthroplasty is performed as an outpatient procedure in select patients. People should first see their primary care doctor and possibly even a specialist such as a cardiologist to make sure they are healthy enough to undergo the procedure, and to make sure their medical condition is optimized. Due to infection concerns, dental work is discouraged for 3 months after surgery, so we suggest having a dental check-up prior to surgery. The local hospitals have preoperative classes for joint replacements surgery that we highly recommend patients attend. If you have been very inactive due to the arthritics condition, we recommend a few sessions of physical therapy prior to surgery to strengthen your muscles and build endurance in order to facilitate the recovery process.

Infection is a feared complication of this surgery. This problem will occur less than 1% of the time, but it will usually mean more surgeries and hospitalizations to effect a cure.  Infections often come from bacteria that living on and in patients.  Recent research has demonstrated that the average human harbors up to 6 pounds of bacteria. For this reason we have our patients do a special scrub to their surgical site and use an antibiotic nasal gel starting prior to the operation. Other factors that have been shown to increase the risk of infection are obesity, poorly controlled diabetes and smoking.  Other risks include blood clots in the leg veins or lungs, heat attack, stroke, and nerve damage.

Components of the Knee Replacement
The knee replacement hardware generally consists of four components. There is a cobalt chromium metal cap that is cemented in place over the end of the thigh bone at the knee (femoral component).   The upper end of the shin bone (proximal tibia) is covered with a metal plate (tibial component) attached to a short stem that is cemented into the top of the tibia.  There is a plastic spacer (polyethylene insert) that goes between the femoral and tibial components, acting as a bearing surface. The knee cap is usually resurfaced also with a polyethylene disk.

kneeReplacement1

Figure on the left depicting an arthritic knee with destroyed joint surfaces.  The figure on the right demonstrates the knee with artificial components in place. 

 

 

Day of the Surgery
Patients come to the hospital on the morning of the surgery to start preparations for the procedure. An IV is started and you will meet with the anesthesiologist. Almost all our patients have a spinal anesthetic, and as a result a breathing tube is not required and you do not need to be attached to a breathing machine. This is some evidence to suggest that the risk of blood clots is reduced when compared with general anesthesia. During surgery, if your health will allow, the anesthesiologist will sedate you and most patients sleep through the operation.

Method of the Procedure
The actual surgery takes approximately 60 to 90 minutes.  An incision is made over the front of the knee to expose the knee joint.  The destroyed joints surfaces of the proximal tibia, distal femur, and patella are shaved off precisely with special cutting jigs and sometimes with the assistance of computer navigation.  The artificial components are cemented in place.  The surgeon must carefully select the right size components, make sure the leg is properly aligned, and that the ligament tension is correct for the operation to be successful.

Hospitalization
After surgery you will go to the recovery room for about 90 minutes prior to going to the orthopaedic floor of the hospital. Most patients who have surgery early in the day are able to get out of bed, walk and go to the bathroom the day of surgery. Oral pain medications are started. All patients will be given medication for the prevention of blood clots. Most patients can just take 325 mg of aspirin daily to prevent blood clots. Patients that are at a higher risk because of prior blood clots or pulmonary embolisms are treated with a stronger oral or injectable blood thinner. A physical therapist will evaluate your needs and design your post-surgical therapy to address your lifestyle when you get back home. If you have stairs or other challenges at home they will make sure you can safely do those things prior to discharge. It is important to begin the process of regaining the ability to bend and straighten the knee.  Currently, the hospital stay is 1 to 3 nights.  Some older patients will need further rehabilitation after the hospital stay. One option is having a home health physical therapist come to your house after discharge. Another option, especially for those without help at home, is going to one of the local nursing homes for further rehabilitation. This is usually covered by Medicare.

At Home
After you are home you will continue to work on the range of motion exercises recommended by the physical therapist in order to regain the ability to bend and straighten the knee. Outpatient physical therapy is often recommended to facilitate the recovery process.  You will continue to use the walker or crutches until it is safe to progress to a cane, and finally no external support.  Most people will feel that they are doing pretty well by three months after surgery.

 

Resources
For more information about Rocky Mountain Orthopaedic Associates Joint Replacement team, go to: http://www.rmodocs.com/specialties/joint-replacement/.

For more information about total knee replacement from the American Academy of Orthpaedics Surgeons go to:  http://orthoinfo.aaos.org/topic.cfm?topic=a00389