Are you worried you might have fluid on your knee?

What does fluid on the knee even mean

f either sentence rings true for you, this post should help provide answers. 

The reality is that knee pain and swelling can be signs of an underlying condition that needs to be investigated, sometimes as a matter of urgency if the pain is felt with it. 

Does fluid on the knee go away by itself?

Underlying Cause

So, to answer the initial question, does fluid on the knee go away by itself

The answer is yes, it can.

In some cases, fluid resolves independently, but fluid warrants further investigation in others.

This is because fluid on the knee is a common side effect of injury, infection, and even some autoimmune diseases.

In this blog post, we’ll go a bit deeper and explore what causes fluid on the knee, the symptoms of it, how it’s diagnosed, and the possible treatment options.

From rest, medications, massage, or surgery. Learn about managing fluid on the knee to get the relief you so desperately need.

What is fluid on the knee?

Fluid on the knee is a term to describe a collection of fluid in or around the joint space between the thighbone and shinbone, collectively known as the knee joint. 

It’s also known as a knee effusion, water on the knee, a small amount of fluid, or a swollen knee, depending on which medical unit you visit (or which page you read online!)

Excess fluid anywhere in the body is often painful and downright uncomfortable, leading to increased tightness and possibly even heat build-up in the affected area. 

In the knee itself, fluid frequently leads to walking issues, leg weakness, and potential concerns with performing daily activities. 


The most common causes of a swollen knee

Many different acute or chronic conditions cause fluid in the knee joint. This is why, regardless of whether pain accompanies it or not, it’s important to be seen by your health care provider. 

Often, fluid on the knee is a side effect of an underlying disease, hence the need to investigate further. 

The most common causes include (but are not limited to:)

  • Knee injury or trauma to the knee joint
  • Ligament injury
  • Chronic swelling from a blood clot
  • Reduced joint movement
  • Fractures
  • Sprains
  • Bruising
  • Infections
  • Autoimmune disease
  • Arthritis (Osteo)
  • Septic arthritis
  • Cysts and lesions (a baker’s cyst is relatively common)

What are the symptoms?

Symptoms of fluid on the knee typically include:

  • Pain
  • Visible swelling
  • Tightness
  • Warmth/heat build-up
  • Difficulty sleeping at night
  • Troubles with standing on the swollen leg

Depending on the amount of fluid in the knee, symptoms range from pain (either mild to severe pain), knee swelling, and/or difficulty walking or moving the knee. 

It depends on where on the knee the fluid is. If it’s at the back of the knee, then the feeling of it may be different from joint fluid in the central aspect of the knee. 

This is why the cause of the swelling needs to be determined. If ligament injuries are causing the swelling, then surgery may be necessary.

If the swelling is a sign of infection, then this needs immediate medical attention. 

If a popliteal cyst in the lower leg is causing swelling further up the leg as excess fluid collects, this would be a different treatment pathway. 

Therefore, if you ask me, a medical professional must examine every type of swelling or knee fluid collection to understand what’s causing it.

The most familiar symptom of fluid on the knee is swelling around the joint area, but visible swelling only happens when a large amount of fluid is present. 

In many cases, fluid on the knee goes undiagnosed simply because the knee still looks normal despite feeling otherwise.

Knee swelling often occurs suddenly, particularly after an injury. Other times, with rheumatoid arthritis, the fluid develops slowly over time, in which case it may be harder to notice.

Other symptoms include tenderness and redness around the joint, stiffness in the affected area, and a feeling of warmth in the knee, which may signal infection. 

In addition to the physical symptoms, those with fluid on the knee may also find it difficult to sleep at night due to the feeling in the knee from the fluid (pain or tightness) and decreased range of motion in the affected leg.

How is fluid on the knee diagnosed?

The simplest (and most specific) way of getting fluid on the knee diagnosed is through the use of medical imaging tests such as X-rays, CT scans, ultrasounds, and/or MRIs. 

These modalities are used to examine the knee area and rule out possible issues causing pain or swelling. 

Alternatively, a joint aspiration involves taking a fluid sample and all excess fluid from the affected area, which can then be tested for white blood cells with signs of infection.

Blood tests may be requested to see if an underlying health condition is responsible for the symptoms.

In some instances where damage inside the joint needs to be evaluated, doctors may order a knee arthroscopy, a procedure that involves inserting a miniature camera into the joint space through small incisions to identify abnormalities or damage causing fluid buildup.

If you’re experiencing any knee symptoms with suspected fluid, it’s important to seek medical attention right away so you can get an accurate diagnosis and begin treatment ASAP.

Early intervention helps avoid permanent damage caused by untreated accumulation around your knees.


Treatment options

Fluid on the knee is treated in different ways, depending on the cause and severity.

The most common treatment option is what the doctors call ‘conservative management.’ 

The acronym ‘RICE’ is good for remembering what you must do. 

It stands for:

  • Rest
  • Ice
  • Compression
  • Elevation 

Non-steroidal anti-inflammatory drugs (NSAIDs) may also be prescribed to reduce pain and inflammation.

A knee brace supports the joint for known knee injuries that result in excess fluid buildup. 

This helps limit movement and reduce further injury while allowing some range of motion. 

In more severe fluid cases, aspiration of excess fluid or an injection of medication to reduce swelling may be required. 

It’s essential to consult your healthcare provider when deciding the best course of action for treating fluid on the knee. 

Trust their judgment, as they are the experts! 


To answer the initial question: Yes, in many cases, fluid on the knee goes away on its own.

But fluid on the knee sometimes requires medical intervention to help it resolve, so I say playing it safe is best.

Whatever symptoms you’re experiencing, make sure you get checked by a doctor, enabling the best possible outcome for healing and recovery. 

If you’d like to read more posts on knee health, I recommend these:

What does a torn MCL feel like?

How to strengthen knee tendons and ligaments

And for more interesting reads, click here.

About the Author

Hi there! I’m Dr. Keagen Hadley, OTD, OTR/L. Straight out of the University of Mary, I’m all about blending my know-how in knee health, well-being, and medical technology. As a licensed occupational therapy doc, I’m here to translate complex concepts into clear, actionable insights – whether it’s knee care or groundbreaking healthcare tech.

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