Pain After Knee Replacement Surgery

Some people experience pain after knee replacements, which 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 osteoarthritis, a common diagnosis that affects some 32 million people in the United States.

During knee replacement surgery, damaged bone and cartilage are removed and the joint is reshaped with metal implants to allow for smooth, pain-free movement. Yet up to 20% of people are dissatisfied with surgery and continue to experience pain and mobility issues.

This article explains some of the reasons for why there may be so much pain after knee replacement, including infection or a bone fracture around the replacement. It explains how persistent pain around the newly replaced joint is diagnosed and treated.

Causes

The most important step in finding a solution to persistent discomfort is to first determine the cause of the pain. Without this information, 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. And 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.
• Kneecap problems: Patellofemoral (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: A poorly aligned implant may not function well, no matter the brand, but researchers note "the relationship between alignment and knee function remains elusive." More research is needed to better understand implant alignment.
• Nerve damage: Nerve injuries can occur during surgery and may lead to permanent pain. A neuroma (pinched nerve) following knee replacement surgery is common.

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

Diagnosis

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.

Start-up pain (pain when rising to stand up) usually resolves within a few months, but other types of pain may suggest a more serious condition. In some cases, the location and timing of the pain can help a healthcare provider pinpoint the underlying cause.

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.

Imaging

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.

Treatment

Treatment for pain after knee replacement is based on the cause. Medications and physical therapy may be a first step but they don't always resolve the underlying problem.

If loosening, infection, or alignment issues are suspected, a revision knee replacement may be necessary. The revision surgery may be minimally invasive or require removing the implanted knee and starting over.

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.

Summary

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.

Causes of pain linked to knee replacement include infection, alignment problems, metal allergy, and more. A healthcare provider will diagnose your pain on the basis of your symptoms and test results.

While situations that cause so much pain after knee replacement are unusual, they can be frustrating. Seek a careful and extensive expert evaluation before making decisions about your knee replacement pain and further treatment options.