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Knee replacement is overall a very safe procedure. However, patients should be aware that there are risks associated with knee replacement. The biggest risks after knee replacement surgery are infection and stiffness.


Infection is uncommon after knee replacement. However, when it occurs, it can be very disruptive to the patient's life. Treatment of infection around a knee replacement usually requires removal of the knee replacement, installation of an antibiotic knee replacement for 3 months and later a third operation to place a new permanent knee replacement.

We take several steps to prevent infection before, during and after the surgery, and the University of Maryland is a leader in research into how to prevent and treat knee infection.


Stiffness is another uncommon but possible complication of knee replacement. Most patients who decide to undergo knee replacement are not able to fully straighten the leg before surgery. In general, knee replacement allows them to straighten the leg all the way.

Most patients after knee replacement are able to bend the leg to the same degree as they were able to before surgery. However, knee replacement does not usually provide people with more knee bending than they had before the operation. Some patients are exuberant scar tissue formers who have less motion in the knee after knee replacement surgery than before.


Instability is one of the main reasons to undergo knee replacement. In most cases, the stability of the knee replacement is better than that of the preoperative arthritic knee. However, some patients experience instability after knee replacement or develop it over time and need to have the knee replacement redone to improve its stability.

Incomplete Relief of Pain

Although knee replacement is very effective at relieving pain, approximately 5% to 10% of patients who undergo knee replacement still have pain afterward. This could be as minimal as occasional pain on cold days, or it could be pain with climbing stairs or level walking.

It is important to understand that the vast majority of patients are very happy with the pain relief achieved with knee replacement, but there is a small subset of patients who have persistent pain after knee replacement.

Nerve and Artery Damage

The knee is surrounded by major nerves and arteries, and it is sometimes possible for them to be injured during surgery. With the worst injuries, the patient can lose the leg. Fortunately, this is very rare and specific steps to avoid it are taken during surgery.

Medical Complications

Medical complications of knee replacement surgery are uncommon but can include blood clots in the lung or leg, heart attack, stroke and even death. These risks are minimized by optimizing the patient's weight and medical status before the operation in conjunction with the primary care doctor. The noted risks are all very rare, but it is important to know that they are possible.

Signs That It May Be Time to Consider Knee Replacement

Knowing the risks, when is it time to have the operation? Below are reasons to consider knee replacement.

Marked Disruption of Everyday Activities

One of the main reasons to consider knee replacement is pain that markedly limits everyday activities despite the use of pain-relief medications. To consider surgery, the patient should feel that the knee pain markedly impacts everyday activities and/or causes the patient to stay in the house more to avoid activity altogether.

Inability to go up and down stairs and the need for a cane are also signs that it may be time to consider knee replacement. If pain-relief medications fail to alleviate pain and bone-on-bone arthritis causes pain on an hourly basis, it is probably time to consider knee replacement for pain relief.

Many patients have trouble sleeping at night because of the pain of knee arthritis. If pain-relief medications fail to allow patients to sleep, it may be time to consider knee replacement.

Bone-on-Bone Arthritis

Before considering knee replacement, the patient should have x-rays that show bone touching bone somewhere in the knee. Patients who have thinning of the cartilage but not bone touching bone should not undergo knee replacement surgery except in rare circumstances.

The reason is that patients who do not have bone-on-bone arthritis but undergo knee replacement are much less likely to be satisfied with the knee replacement. We should find some other pain management strategy to help with their symptoms.


Part of knee arthritis is progressive instability of the knee that causes the knee to become much looser and more unstable than it was before developing arthritis. In some cases, this is mild. In other cases, it is substantial enough that it becomes markedly unstable, particularly when the knee is bent.

Many times, this is manifested as a “giving way” sensation to the knee. In severe cases, the knee instability causes the patient to fall. It is our feeling that for patients with bone-on-bone arthritis who have started to experience falls because of the knee arthritis, it is probably time for knee replacement to improve the stability of the knee and limit the chances of falling.


Knee replacement surgery is an extremely successful operation that has helped millions of patients. It is important for patients to be aware of the associated risks. However, the risks are generally very rare, with the exception of incomplete relief of knee pain experienced by 5% to 10% of patients who undergo knee replacement surgery.

The vast majority of patients are happy they underwent the procedure. Only the patient can decide when he or she is ready for knee replacement. In most cases, knee replacement is an entirely elective procedure that can be done with no rush. The one exception is the patient who is starting to fall frequently because of an unstable knee.

Patients who have knee arthritis and are starting to fall should strongly consider surgery. Knowing the risks, benefits and options will help you to be part of the care team and get the most out of your knees.