Pain After Knee Replacement

Why Does Your Knee Still Hurt?

pain knee elderly PT
Pain After Knee Replacement. kali9 / Getty Images

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 smooth, pain-free movement of the joint.

When a knee replacement is performed and the rehabilitation has been completed, more than 90% of patients will rate their outcome as good or excellent. However, not everyone has a pain-free knee after the procedure. While the satisfaction following this surgery is excellent, not everyone considers their result to be a full success. 

About 10% of patients will not consider their surgery a complete success. Some complications of knee replacement are obvious. Patients who have an infection in their replacement or fracture the bone around their replacement are expected to have less successful results. However, the most common reason people complain of poor results is not a major infection or fracture, but rather persistent pain around their newly replaced joint.

Causes of Pain After Knee Replacement

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 or Wearing 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 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.

    Evaluating Pain After Knee Replacement

    Your surgeon will take several steps to evaluate your pain. The first step is talking to you. Pain can have many different qualities, and the type of pain can help you and your doctor to understand the underlying cause. For example, pain when first getting up (start-up pain) is common after a knee replacement but usually resolves after a few months. Persistent start-up pain can be a sign of loosening of an implant. Pain when going up and down stairs is suggestive of a kneecap problem.

    Your surgeon will then 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 MRI 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. MRIs can be performed with specific techniques that help to evaluate structures that are close to a prosthetic implant. Laboratory studies can show signs of a subtle infection. Laboratory studies that are sometimes performed include markers of inflammation such as ESR and CRP. Elevations of these markers of inflammation can indicate an infection although they have male so be elevated with a variety of other medical conditions. Not every person who has pain after knee replacement requires the same evaluation. Depending on your symptoms, your doctor may target the evaluation to specific causes of pain after knee replacement.

    One of the most commonly performed tests for a painful knee replacement is to insert a needle into the knee joint, to obtain some fluid from around the implant. This fluid, called synovial fluid, can be analyzed in the laboratory to specifically look for signs of infection within the knee joint. Test performed on synovial fluid include a white blood cell count analysis, Gram stain, and bacterial cultures. If the bacterial culture is positive, there is likely infection around the knee replacement implant. If the white blood cell count is significantly elevated, this is also concerning for infection of the knee replacement.

    Timing of Pain after Knee Replacement

    One of the important clues to identifying the source of pain after knee replacement surgery is the timing of the increase in symptoms:

    • Did the pain occurred gradually over time, or abruptly?
    • Was the knee replacement weeks ago? Months ago? Years ago?
    • Are the symptoms worsening, or are they just persistent?

    Answers to each of these questions can help guide your orthopedic surgeon to identify the source of your pain. Symptoms that occur abruptly tend to be the result of acute injuries, such as fractures. Symptoms that occur more gradually over the course of months and years are more commonly related to issues with the implant wearing out or coming loose.

    When people have pain in the weeks and months following knee replacement, concerns about infection and healing problems are typically on your doctors mind. In the years following joint replacement, the concern tends to be implant issues such as wearing out and loosening.

    Treatment of a Painful Knee Replacement

    As stated before, the most important step is understanding the cause of pain, since blindly trying to treat 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 it may require removing the implanted knee and starting over. Sometimes the decision to treat pain after knee replacement is urgent, while other times, giving the new knee some time to adapt can be appropriate. Your surgeon can help to guide you on the most appropriate treatment for the cause of your pain. There are a few situations, where the source of pain cannot be identified. In these situations, treatment is almost always nonsurgical, as performing revision knee replacement without knowing why the knee is not working properly, is unlikely to lead to improvement.​​

    A Word From Verywell

    Pain after knee replacement is incredibly frustrating for many patients. While the vast majority of knee replacement surgeries leads 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 are incredibly frustrating for the patient to experience this complication. A systematic evaluation, a second opinion, and a progression of treatments can help people who have pain after a knee replacement hopefully find relief from her discomfort. It is important that these individuals approach their treatment patiently, as resolving this type of pain often takes time. The most important rule of thumb when considering surgery for a painful knee replacement is that the underlying cause of pain should be known for a surgical procedure. Performing surgery without clearly understanding the source of discomfort is unlikely to lead to improvement.

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