Updated August 04, 2014.

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

In 1988, when I was just 33 years old, my orthopedic surgeon said to me, "You need two new knees. I will do bilateral total knee replacements for you. Don't worry. You'll love it."  I was a bit shocked, as you can imagine, but I trusted this surgeon more than any human on the planet. He really didn't give me any options to repair the damage that rheumatoid arthritis had caused. Turned out, he was right.

I had the surgery and I did love my new knees. The procedure did what it was supposed to do -- relieve pain associated with knee arthritis and restore function.

Over time, I learned there are options for knee replacement. Most people who have both of their knees replaced, do one at a time. Bilateral total knee replacement is actually not common. There also is the option of having a partial knee replacement. 

What Is a Partial Knee Replacement?

The knee is divided into three major compartments: the medial compartment (inside part of the knee); the lateral compartment (outside part of the knee); and the patellofemoral compartment (front of the knee formed by the kneecap and femur). Some arthritis patients have damage in only one of the three compartments of the knee. Most commonly, when only one compartment is affected, it is the medial compartment. A partial knee replacement, also referred to as a unicompartmental knee replacement, may be an appropriate option for certain patients with damage in only one compartment.

Good candidates for partial knee replacement usually have osteoarthritis.

A total knee replacement, in which all three compartments of the knee are replaced, is typically the better option for patients with inflammatory types of arthritis (e.g., rheumatoid arthritis) or other arthritic conditions which involve damage to more than one compartment. On a case-by-case basis, other factors may be considered when deciding between a partial or total knee replacement (e.g., if the patient is morbidly obese).

The American Academy of Orthopaedic Surgeons (AAOS) recognizes that there are advantages of partial knee replacement over total knee replacement, including quicker recovery time, less post-op pain, and less blood loss during surgery. But, there are disadvantages as well. 

Disadvantages of Partial Knee Replacement 

Study results published in The Lancet on July 8, 2014 compared adverse outcomes of partial knee replacement to those associated with total knee replacement. The study, said to be the most comprehensive comparison to date of the two procedures, found that there was a significantly higher risk of revision surgery or re-operation with partial knee replacement than total knee replacement. But, patients having total knee replacement had a greater risk of complications. Total knee replacement patients were approximately twice as likely to have a venous thromboembolism (blood clot), heart attack, or deep infection than those having partial knee replacement. Total knee replacement patients were almost three times more likely to have a stroke and they were 4 times more likely to require a blood transfusion than partial knee replacement patients. Also, based on the findings of this study, researchers concluded that total knee replacement patients were about 4 times more likely to die within the 30-day period following surgery and 15% more likely to die within the first 8 years after surgery compared to partial knee replacement patients.

With total knee replacement, inpatient stays were longer and re-admissions were more likely to occur. With regard to revisions of total knee replacement, most were due to loosening of hardware or infection. With revisions of partial knee replacement, most were related to loosening, pain, or progression of arthritis. Most revisions of partial knee replacements were conversions to total knee replacements. Revisions of total knee replacements tend to be complicated procedures involving the insertion of larger components to enhance stability.

The Bottom Line

Partial knee replacement is associated with shorter hospital stays, fewer complications, fewer re-admissions, and a decreased risk of mortality. But, partial knee replacement does have a higher risk of revision and re-operation. A systematic review of scientific literature confirmed a higher rate of revision for partial knee replacements. Revision rate should not be the only factor considered when deciding between the two procedures though. If you are a candidate for knee replacement, your orthopedic surgeon will advise you regarding the appropriateness of partial or total knee replacement in your case.

<sub>Sources:

Adverse outcomes after total and unicompartmental knee replacement in 101,330 matched patients: a study of data from the National Joint Registry for England and Wales. The Lancet. Liddle AD et al. Published Online July 8, 2014.
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2814%2960419-0/fulltext

Unicompartmental Knee Replacement. OrthoInfo. AAOS. June 2010.
http://orthoinfo.aaos.org/topic.cfm?topic=A00585

Partial Knee Replacement. Hospital for Special Surgery. Alexiades, Boettner, and Pearle. February 13, 2013.
http://www.hss.edu/conditions_partial-knee-replacement.asp#.U8GuDbEjR8E</sub>