Pain After Knee Replacement Surgery

Causes, Diagnosis, and Treatment Options

Knee replacements are among the most commonly performed and highly successful orthopedic surgical procedures. A knee replacement is done when the knee joint has worn out, most often as a result of wear-and-tear arthritis.

When a knee replacement surgery is performed, the worn-out cartilage is removed and the ends of the bone are shaped. Over the ends of the bone, a metal implant is fit into place, and a plastic spacer is placed between the metal implants. This reconstructive procedure is performed to allow a smooth, pain-free movement of the joint.

When a knee replacement is performed and the rehabilitation has been completed, more than 90% of recipients will rate their outcome as good or excellent. However, not everyone has a pain-free knee after the procedure. About 10% will be less than satisfied with the results.

Some of the reasons for dissatisfaction are obvious, including postoperative infection or a bone fracture around their replacement. However, the most common reason is the development of persistent pain around the newly replaced joint.

Physical therapist and patient working on knee exercises
kali9 / Getty Images


The most important step in finding a solution to persistent discomfort is to first determine the cause of the pain. Without this knowledge, it is very difficult to find an appropriate treatment. The most common causes of pain after knee replacement include:

  • Loosening of the implant: This is most often the cause of pain years or decades after the knee replacement; however, it is seldom the cause of persistent pain right after surgery.
  • Infection: Infection is a serious and worrisome concern. Any increase in pain after knee replacement should raise concerns for infection. Most often, the signs of infection are obvious, but subtle infections may be the cause of persistent discomfort.
  • Patellofemoral (kneecap) problems: Kneecap problems are a common cause of knee replacement pain. Significant forces are applied to the kneecap, even with normal activities, such as getting up from a chair or walking down the stairs. Getting a kneecap to perform well with a replacement can be technically challenging even for a skilled surgeon.
  • Alignment problems: Many patients focus on the knee replacement implant brand or type. But most surgeons will tell you the brand matters much less than how well the implant is put in. A poorly aligned implant may not function well, no matter the brand. Surgeons are investigating if computer navigation will help improve implant alignment.

Other issues that can cause persistent pain include bursitis, complex regional pain syndrome, and pinched nerves.


Your surgeon will take several steps to evaluate your pain. The first step simply involves talking with you and discussing your pain. Pain can have many different qualities, and the type of pain described can help your doctor make an accurate diagnosis.

While pain when rising—known as start-up pain—usually resolves within a few months, other types of pain may suggest a more serious condition. In some cases, the location and timing of the pain can help a doctor pinpoint the underlying cause.

Common Diagnostic Signs

These signs can aid your doctor in a diagnosis:

  • Persistent startup pain can be a sign of a loosening implant.
  • Pain when navigating stairs suggests a kneecap problem.
  • The sudden appearance of pain suggests a fracture or injury.
  • Pain accompanied by swelling, redness, and fever are strong indications of an infection.
  • A deformed kneecap is a sign of a patellofemoral problem.

Your surgeon will then want to examine the knee. A physical exam can help identify infection, stiffness, and alignment issues. Ensuring that the mechanics of the knee replacement are sound is important. Just like having the proper alignment in your car, it is important that the knee replacement is properly aligned and balanced.


X-rays and other studies can assess alignment and loosening. Subtle loosening may not show up on a regular ​X-ray, and a bone scan or magnetic resonance imaging (MRI) scan may be performed. In addition, there are specialty imaging studies that can be performed specifically to assess for problems related to the knee replacement.

X-rays performed fluoroscopically (in real-time) and stress radiographs to evaluate ligaments are sometimes performed. MRI is better suited for soft tissue injuries and can be particularly useful if there is infection or inflammation related to bursitis or tendonitis.

Lab Tests

Laboratory studies that are sometimes performed include markers of inflammation such as erythrocyte sedimentation rate (ESR) and a C-reactive protein (CRP) tests. Elevations of these markers of inflammation can indicate an infection or other inflammatory medical conditions.

One of the most commonly performed procedures for a painful knee replacement is arthrocentesis (joint aspiration). This involves the insertion of a needle into the knee joint to obtain some fluid from around the implant.

The fluid, called synovial fluid, can be analyzed in the lab to look for signs of infection or abnormal crystallization around the knee joint. Tests commonly performed on synovial fluid include a white blood cell count (WBC), bacterial gram stain, and bacterial cultures.

According to a 2012 study from France, infection occurs in between one percent to three percent of knee replacement surgeries and is the leading cause of knee revision surgery.


The most important step is understanding the cause of pain since blindly treating pain without knowing the cause is unlikely to lead to a good result. In some situations, pain may be treated with medications and physical therapy.

In other cases, particularly if loosening, infection or alignment issues are suspected, another surgery called a revision knee replacement may be necessary. The revision surgery may be minimally invasive or require removing the implanted knee and starting over.

Sometimes the decision to treat pain after knee replacement is urgent, while, at other times, giving the new knee time to adapt may be more appropriate. Your surgeon can help to guide you on the most appropriate treatment for the cause of your pain.

There are situations where the source of pain cannot be identified. In such instances, it is best to treat the condition conservatively since revision surgery is unlikely to lead to an improvement.​​ If in doubt, seek a second opinion.

A Word From Verywell

While the vast majority of knee replacement surgeries lead to relief of pain, there are some people who do not find relief, and sometimes the pain can even be worse than it was before surgery.

While these situations are unusual, they can incredibly frustrating. Even so, it is important to remain patient and not rush to judgment without a careful and extensive expert evaluation. Doing so may expose you to unnecessary expenses, additional frustration, and leave you in no better condition than when you started.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Jonathan Cluett, MD
Jonathan Cluett, MD, is board-certified in orthopedic surgery. He served as assistant team physician to Chivas USA (Major League Soccer) and the United States men's and women's national soccer teams.