Recent Blog Articles
Talking to your doctor about your LGBTQ+ sex life
Untangling grief: Living beyond a great loss
Thunderstorm asthma: Bad weather, allergies, and asthma attacks
Heart problems and the heat: What to know and do
I’m too young to have Alzheimer’s disease or dementia, right?
Period equity: What it is and why it matters
Back pain: Will treatment for the mind, body—or both—help?
Colon cancer screening decisions: What’s the best option and when?
Cognitive effects in midlife of long-term cannabis use
If climate change keeps you up at night, here's how to cope
Persistent Knee Swelling in the Adult
Welcome to this Decision Guide about persistent knee swelling. We're sorry to hear you have this problem!
The goal of this guide is to provide information while awaiting evaluation with your doctor for persistent knee swelling or for additional information after you have seen him or her. Please keep in mind that this guide is not intended to replace a face-to-face evaluation with your doctor.
First, some background information about this guide and about knee swelling:
Knee swelling may develop for a number of reasons. If you have new, unexplained knee swelling that followed a significant injury or you have fever, this guide is not the best place to start! See your doctor first. Ligament tears, cartilage damage and fracture can follow trauma and may require urgent treatment; this is particularly true if you are unable to bear weight.
This decision guide will focus on persistent knee swelling -- that is, knee swelling lasting more than two or three weeks.
You'll be asked a series of questions and depending on your answers, information will be provided and additional questions asked until the conclusion.
So, let's get started.
Would you like to get information related to your own situation? Or would you rather start with some general information about knee swelling?
In general, one or both knees may be swollen due to
increased joint fluid
blood in the joint
enlargement of the bones near the knee joint
swelling near the knee joint (without an actual joint problem)--for example, bursitis can cause swelling directly on top of the kneecap
fluid behind the knee, called a Baker's cyst.
Each of these will be briefly reviewed. There are other, rarer, causes that will not be covered here.
Let's start with Increased Joint Fluid:
Normally, there is a tiny amount of fluid in the knee which serves as a lubricant and to deliver nutrition to the cartilage that lines the joint. When there is any type of arthritis present, fluid may accumulate in the joint. This is sometimes called "water on the knee." In addition to arthritis, structural problems in the knee (such as torn cartilage or ligament injury) may stimulate extra fluid formation.
Your doctor may recommend a procedure (called arthrocentesis, or joint aspiration) in which a sample of fluid is removed from the knee and analyzed for the presence of white blood cells, red blood cells, infection, or crystals.
This is helpful because certain diseases can be suggested or even proven by the results of this analysis:
high white blood cell count in joint fluid suggests the presence of marked inflammation (making infection a larger concern).
a large number of red blood cells suggests there's been bleeding into the joint.
many common bacterial joint infections can be identified by analysis of the fluid.
gout or pseudogout, the most common forms of "crystal-induced" arthritis, can be proven by seeing the appropriate crystal (uric acid crystals in gout; calcium crystals in pseudogout).
Would you like to continue learning about other causes of joint swelling (next up: blood in the joint) or would you prefer to move on to questions about your particular situation?
To continue reading this article, you must log in.
Subscribe to Harvard Health Online for immediate access to health news and information from Harvard Medical School.
- Research health conditions
- Check your symptoms
- Prepare for a doctor's visit or test
- Find the best treatments and procedures for you
- Explore options for better nutrition and exercise
I'd like to receive access to Harvard Health Online for only $4.99 a month.Sign Me Up
Already a member? Login ».
As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles.
No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.
Free Healthbeat Signup
Get the latest in health news delivered to your inbox!