Many patients will struggle with knee pain in their lives, so it’s a common problem for doctors to see. It may be pain that has been happening for several years, or it may be new pain. Knee arthritis is the most common cause of knee pain.

Knee arthritis is caused when the cartilage in the knee becomes damaged or lost so the joint doesn’t move smoothly and comfortably together.

We always try to avoid surgery when possible. Physical therapy, home exercises, weight loss, medications and injections are all strategies we try before progressing to surgery. However, when those treatments are no longer helping and the arthritis is more severe, surgery is the best treatment.

Introduction to Replacements

The knee is divided into 3 compartments:

  • Medial compartment, or inside of the knee
  • Lateral compartment, or outside of the knee
  • Kneecap

One compartment of the knee may be damaged, or more than one may be damaged. A knee replacement removes the damaged part of the knee and replaces it with metal and plastic pieces so the knee can move smoothly and without pain.

Partial Knee Replacements

A partial knee replacement replaces only one compartment of the knee. The medial compartment on the inside of the knee is the most common part of the knee to have advanced arthritis, so it’s the most common place to have a partial knee replacement.


  • Only replaces the one portion (compartment) of the knee that is damaged
  • Less invasive surgery with a smaller incision
  • Easier to recover
  • Less difficulty with range of motion
  • Less therapy needed
  • Can easily go home same day of surgery
  • Less pain
  • Feels like “more normal” knee


  • Can be more technically challenging
  • Not everyone is a candidate
  • Can develop arthritis in remainder of the knee

Total Knee Replacements

A total knee replacement replaces all three compartments of the knee.


  • Replaces all 3 parts (compartments) of the knee
  • Less chance of developing arthritis in knee
  • More commonly performed
  • Very good results
  • More patients are candidates


  • More invasive surgery
  • Can “feel” more artificial
  • Takes a little longer to recover
  • Usually have more pain during recovery
  • Many patients require brief hospital stay

Important Points

  • Knee pain is very treatable, so if you’re having knee pain, especially knee pain that is affecting your quality of life, seek treatment.
  • Treatment for knee pain does not necessarily involve surgery.
  • Surgery is available if needed. You and your surgeon can discuss the correct type of surgery for you.

Frequently Asked Questions

If you have arthritis in two compartments of your knee, what kind of replacement is done?

Some surgeons will do a bicompartmental knee replacement and replace two compartments of your knee, instead of the single compartment with a partial knee replacement and all three compartments with a total knee replacement. However, this surgery is not performed frequently. Most surgeons would have the patient do a total knee replacement.

Can you run after a knee replacement?

Yes, you can. The traditional teaching was to discourage running on a knee replacement, with the idea that the knee replacement would wear out sooner. However, there is not great evidence to support that idea. If running is important to a patient’s life, I would have a discussion with them about the potential of the replacement wearing out earlier, but they can still run.

Is general anesthesia required?

It is not required for most people. The majority of my knee surgery patients do not have general anesthesia. Other types of anesthesia are used instead.

Are the ACL and PCL left in place in a partial knee replacement or a total knee replacement?

With a partial knee replacement, the ACL and PCL are left in place to help the knee function in a more normal fashion. For some designs of partial replacement protheses, you cannot have the surgery if you are missing an ACL. However, if someone is missing an ACL, usually they have other problems in their knee that make a total knee replacement a better choice.

In a total knee replacement, the ACL and the PCL are usually removed. When I’m inside a knee during surgery I look at both ligaments, and they usually are damaged in some way.

After surgery, do you have to take anti-rejection medication for a knee replacement?

No, anti-rejection medications are not needed after a joint replacement.

Can you have two knee replacements at the same time?

It’s possible to have two knee replacements at the same time, but it’s not common. I advise against replacements at the same time because they may not be as safe for the patient as doing the replacements one at a time. Recovery is also more difficult with both legs having been operated on.

What happens if a patient is scheduled to have a partial knee replacement but the surgeon discovers during surgery that a total knee replacement is needed?

I always discuss this possibility with my patients. Usually imaging like x-rays and exams can tell your surgeon before surgery which parts of the knee need to be replaced, but surgeons aren’t infallible. If during surgery your surgeon discovers that a total knee replacement is needed instead of a partial knee replacement, they will do a total knee replacement. The operating room for a partial knee replacement will also have the equipment for a total knee replacement ready just in case.

How long does a total knee replacement last? What are the signs it is failing?

It’s difficult to say for a specific individual how long their knee replacement will last. We can look at large groups of data and make predictions about most people, however. About 20 years ago there was an advance in the technology used for replacements, so the replacements are lasting longer than they used to. About 15 years out from surgery, 85% of knee replacement patients have not had another surgery on their knee. I would expect replacements to last 15-25 years, but I can’t say if in a specific patient their replacement will last that long.

Pain is the primary symptom of a knee replacement failing, particularly pain that doesn’t go away or that gets worse with some activity. It may be accompanied by swelling, loss of range of motion, or a feeling of weakness.

Do the types of activities a patient does influence the type of replacement used?

No, a patient’s activities don’t influence the prosthetic. Surgeons choose the type of replacement used based on what they are comfortable and what they are familiar with, and the size that fits the patient.

Some types of replacements are patient-specific and are decided beforehand with advanced imaging like a CT scan, but those are less common for knee replacements.