Knee replacement is a surgical procedure that decreases pain and improves the quality of life in many patients with severe arthritis of the knees. Typically patients undergo this surgery after non-operative treatments (such as activity modification medications knee injections or walking with a cane) have failed to provide relief of arthritic symptoms. Surgeons have performed knee replacements for over three decades generally with excellent results; most reports have ten-year “success rates” in excess of 90 percent. Broadly speaking there are two types of knee replacements: total knee replacements  and Partial (or unicompartmental) knee replacements.

While it may seem appealing to have half of a surgery compared to a full surgery, it is important to understand the differences between a unicompartmental (partial) and a total knee replacement surgery. Each type of knee replacement surgery is unique and has its own outcomes after surgery.The knee is composed of three compartments: the inside (medial), outside (lateral) and underneath the knee cap (patellofemoral/anterior). Each of these compartments can be replaced individually in partial knee replacement surgery, or all three can be replaced in total knee replacement surgery*. A partial knee replacement is technically one-third of the surgery of a total knee replacement. If you have a partial knee replacement, you will find improvement in the function of your knee, but there are some long-term factors to consider.

Partial Knee Replacement is an alternative to total knee replacement for patients whose disease is limited to just one area of the knee.Because a partial knee replacement is done through a smaller incision, patients usually spend less time in the hospital and return to normal activities sooner than total knee replacement patients.There are a range of treatments for knee osteoarthritis and your doctor will discuss with you the options that will best relieve your individual osteoarthritis symptoms.

Because a partial knee replacement is less surgery, it has often been reported to have an easier, quicker, more complete recovery and greater satisfaction than a full knee replacement.2  Complications during surgery like blood loss, transfusion and blood clots tend to be less with a partial replacement;3 however, long-term studies show the lifespan of partial knee replacement components is not as long as the lifespan of components used in a total knee replacement.4,5Because partial knee replacement retains most of your knee tissue, you are still susceptible to meniscal tears and progression of arthritis in the rest of the knee. When a partial knee replacement fails, it can be converted to a full knee replacement with an excellent degree of success. The surgery and recovery may be more involved, but the overall outcomes are highly successful.6

A knee replacement (also called knee arthroplasty) might be more accurately termed a knee "resurfacing" because only the surface of the bones are actually replaced.There are four basic steps to a knee replacement procedure.
1. Prepare the bone. The damaged cartilage surfaces at the ends of the femur and tibia are removed along with a small amount of underlying bone.
2. Position the metal implants. The removed cartilage and bone is replaced with metal components that recreate the surface of the joint. These metal parts may be cemented or "press-fit" into the bone.
3. Resurface the patella. The undersurface of the patella (kneecap) is cut and resurfaced with a plastic button. Some surgeons do not resurface the patella, depending upon the case.
4. Insert a spacer. A medical-grade plastic spacer is inserted between the metal components to create a smooth gliding surface.

Multiple studies show that a majority of patients who are appropriate candidates for the procedure have good results with unicompartmental knee replacement.The advantages of partial knee replacement over total knee replacement include:Quicker recoveryLess pain after surgeryLess blood lossAlso, because the bone, cartilage, and ligaments in the healthy parts of the knee are kept, many patients report that a unicompartmental knee replacement feels more natural than a total knee replacement. A unicompartmental knee may also bend better.

The disadvantages of partial knee replacement compared with total knee replacement include:Slightly less predictable pain reliefPotential need for more surgery. For example, a total knee replacement may be necessary in the future if arthritis develops in the parts of the knee that have not been replaced.

Both partial and total knee replacements can be highly successfully for patients who are good candidates. It is important to discuss the risks and benefits of each type of surgery with your surgeon so that your expectations are in line with the procedure you elect to have. Remember that both of these procedures are replacements, and you should follow the activity restrictions your surgeon provides you. Neither procedure is designed to hold up to the rigors of high-impact sports. If you take care of your total or partial knee replacement it will provide you with the greatest longevity possible.