Is Partial Knee Replacement Right For You?

Partial knee replacement, also called a unicompartmental knee replacement, is a surgery that may be considered for treatment of severe arthritis of the knee. Traditionally, patients with advanced arthritis of the joint would undergo total knee replacement. In a total knee replacement, all of the cartilage is removed from the knee joint, and a metal and plastic implant is inserted.

The partial knee replacement surgical procedure has generated significant interest because it uses a smaller incision and has a faster recovery than full knee replacement surgery. Partial knee replacement is a type of minimally invasive surgery. The idea is to remove only the most damaged areas of cartilage from the joint and leave any healthy parts of the joint for continued use.

Most often, partial knee replacements use implants placed between the end of the thigh bone and the top of the shin bone. Partial knee replacements can also replace the part of the joint under the kneecap, in what's called a patellofemoral replacement.

Is a Partial Knee Replacement Right For You?

The minimally invasive partial knee replacement is designed for patients who have severe arthritis of the knee and have not found relief with standard non-surgical treatments. The treatments may include oral medications, cortisone injections, strengthening exercises, and weight loss. If these treatments are not sufficient and you are not satisfied, then surgery may be considered.

The partial knee surgery may be possible if the arthritis in the knee is confined to a limited area. If the arthritis is more widespread, then the partial knee replacement is not appropriate and should not be considered. In addition, the partial knee surgery is recommended in patients who are:

• Older than 55 years
• Not overweight
• Not heavy laborers or athletes
• Have intact ligaments (specifically the ACL)

If these criteria are not met, then the minimally invasive partial knee surgery may not be as successful. Unfortunately, many patients are, as a result, ineligible for this procedure.

The Downside of Partial Replacements

Many patients who are interested in a partial knee replacement have arthritis that is too advanced for this procedure. Because surgical treatment is considered a last resort by most patients, by the time surgery is necessary, their arthritis may be too advanced to consider the partial knee surgery.

If partial knee replacement is done in a patient who is a poor candidate, failure rates can be high, and conversion to a total knee replacement may be necessary. Some of the reasons why people are not good candidates are listed above. People with advanced arthritis throughout their knee, people who are overweight, and people whose knee joints are not properly aligned or who have associated knee ligament damage will all do better with a full knee replacement rather than a partial knee replacement.

There is often a temptation to have a partial knee replacement because it is less invasive and the recovery is faster. However, it is important not to overlook the longer-term results; a fast recovery is of no benefit if it doesn't make you better or doesn't last long.

Benefits

• Smaller incision: A traditional knee replacement surgery involves an incision about 8 inches over the front of the knee. There is more significant dissection necessary to complete the procedure compared to the partial knee surgery. In the minimally invasive partial knee replacement, the incision is about 4 inches, and the amount of dissection and bone removal is much smaller.
• Less blood loss: Because of the extent of dissection and bone removal necessary for a total knee replacement, the need for a blood transfusion is relatively common. With the partial knee procedure, a blood transfusion is infrequently needed, and patients do not need to consider giving blood before surgery.
• Shorter recovery: Both the time in the hospital and the time to functional recovery are less with a partial knee replacement. Patients are known to have been discharged on the day of the procedure, although most often patients are discharged on the first or second post-operative day. With traditional total knee replacement, patients seldom leave before three days in the hospital and may require a stay in an inpatient rehabilitation unit.
• Normal knee kinematics: The movement of the knee joint is complex and dependent on the interaction of your joint surface and the ligaments, muscles, and tendons that surround the joint. When a full knee replacement is performed, many of these structures are removed to allow for insertion of the artificial knee joint. In a partial knee replacement, more of these structures remain, and therefore the mechanics and movement of the joint remain closer to normal. In fact, studies have clearly demonstrated that, in people who have had a full knee replacement on one side and a partial on the other side, their partial knee replacement feels more "normal."

The long-term results are very good when partial knee replacement is done in the right patients. Older studies showed less successful results, but these results are thought to be due to poor patient selection.

Conversion to Total Knee Replacement

When patients with a partial knee replacement are properly selected, this minimally invasive procedure is quite successful. That said, some patients continue to develop arthritis in other areas of the knee. In addition, some patients wear out the unicompartmental knee implant, or it can come loose within the knee. All of these situations would require additional surgery, and possibly the conversion to a total knee replacement.

Conversion from a partial knee replacement to a full knee replacement can be more difficult because of the prior surgery, but it is not uncommon, and results of conversion are good.

Other potential problems with partial knee replacement are similar to the risks of all joint replacements, which include infection, blood clots, and problems with anesthesia. It is important to have a discussion with your healthcare provider about the risks of this surgical procedure.

A Word From Verywell

Partial knee replacement is an option for people with knee arthritis that is limited to one part of their knee joint. When the right patient has this procedure, it can give them a normal-feeling knee with a faster recovery than a total knee replacement. However, caution must be used, since a partial knee replacement is not right for everyone with knee arthritis, and—performed in the wrong patient—it can lead to less satisfactory results. If you are facing knee replacement, ask your surgeon if a partial knee replacement might work for you or if you require a full knee replacement.