Water on the Knee – Symptoms, Causes and Solutions

Water on the knee is characterized by the accumulation of fluid and inflammation around the knee joint. When this occurs your knee may appear puffy and larger than usual. You may also find that it feels stiff and painful when you place weight on it and is sore to the touch. All of this can cause discomfort while walking up and down stairs, kneeling, and squatting. If you are experiencing symptoms of water on the knee you should consult your doctor to determine the best course of treatment for you.

Water on the knee is also known as knee joint effusion and swelling.

Water on the knee – Causes

There are a variety of conditions that can cause your knee to become swollen (Table 1). Some of which may be temporary, simply requiring rest, others may require surgery or permanent lifestyle changes.

Chart showing common knee problems by age of occurence
Table 1: Common causes of knee pain and swelling by age

Knee Arthritis – Common Water on the Knee Cause

The two most common types of arthritis are rheumatoid and osteoarthritis. Both of these conditions result in the gradual breakdown of the knee joint – but in two completely different ways. Rheumatoid arthritis occurs when the body’s immune system malfunctions and starts attacking otherwise healthy joint tissue. This leads to the joint to slowly degenerate causing pain and inflammation.

According to the Arthritis Foundation, osteoarthritis is the most common type of arthritis affecting over 31 million Americans. Osteoarthritis is characterized by the breakdown of cartilage between the bones in the knee joint. As the cartilage wears, bone on bone friction begins to occur and eventually results in the formation of bone spurs. The lack of cartilage and abnormal bone growth causes joint swelling, pain, and stiffness. Treatment for osteoarthritis depends on a variety of factors, to learn more about the disease check out: Guide to Osteoarthritis Treatment Options


Gout, known as the disease of kings, affects approximately 2% of Americans and has become more common over time.2 Uric acid crystallization stemming from a build-up of uric acid in the blood is the primary cause of gout. Underlying the excess uric acid production is typically poor functioning kidneys – failing to excrete the acid into the urinary system.3

When the uric acid crystallizes around a joint, it triggers a significant immune response. The onset of pain is unusually rapid and the swelling around the joint is visually apparent. One distinguishing factor with gout is that the pain typically occurs during the night. Risk factors that influence your risk of developing gout are poor diet, high body weight, and genetic factors.3


We have all had infections at one point or another. You may remember the extreme swelling, skin redness, stiffness, and pain. The causes can range from viruses, bacteria to parasites. Many of these organisms live on your skin, therefore any puncture or open wound presents a path for them to enter the joint. Staphylococcus aureus bacteria are one of the most common culprits for joint infections with over 500,000 Americans developing staph infections annually.5 If you suspect that you have an infection consult your doctor immediately as you will likely require antibiotic medicine.  

Prepatellar Bursitis

Bursae are small sacs of lubricating synovial fluid that are deposited in around your joints. They help ensure that tendons, ligaments, and muscles slide past each other with minimal friction. Sometimes due to excessive activity, they can become irritated and begin accumulating an excessive amount of synovial fluid. The prepatellar bursa is a common culprit for those experiencing excessive swelling and pain on the front of the knee cap.


Cysts are kind of like bursae – bubbles of fluid, but different in the sense that they are generally unwanted and form in areas where they increase pressure and friction in the knee joint. An example of this is the baker’s cyst – a common cause of knee pain and fluid build-up at the back of the joint. Here a bubble of synovial fluid causes noticeable localized swelling and may irritate you when bending the knee or squatting frequently. Cysts can resolve on their own, however, in extreme cases, they may need to be removed surgically.


Tumors are similar to cysts in the sense they are unwanted outgrowths that interfere with normal joint function. The main difference is that rather than being full of fluid, tumors are masses of metabolically active cells that can continue to grow. Tumors can be cancerous and non-cancerous. Fortunately, the latter is more common, including mostly harmless cellular outgrowths like skin moles. Tumors around the knee joint are relatively uncommon, but if present they will cause noticeable fluid build-up, joint pain, and stiffness. Surgery is usually required to resolve the issue.

Water on the knee – Solutions  


Rest – Ice – Compression – Elevation. All of these activities help your body’s vascular system in draining fluid and from the affected knee joint. Side effects are minimal and these treatments can be done frequently throughout the day. Learn more about the RICE method.

Non-Steroidal Anti-inflammatory Drugs (NSAID)

NSAIDs like ibuprofen are extremely effective in quickly reducing inflammation and knee pain. That being said there are some potentially negative side effects associated with their long term use. If the nature of your knee condition (e.g. knee arthritis) means that it will be ongoing for a long period of time – you may want to consider a more conservative treatment approach.

Cortisone Injections

Similar to NSAIDs corticosteroids are powerful pharmaceutical drugs that can eliminate inflammation and provide you with temporary relief from your knee pain. While effective for some, there are some possible long term side effects to consider when weighing your options. Learn More: Cortisone Shots in the Knee – Do they Really Work?  


Joint instability and muscle weakness can be contributing factors to knee swelling and pain. Engaging in regular lower-body resistance training and aerobic exercise can be a low risk, low-cost method of treating knee pain particularly if the underlying cause is arthritis. Learn more about exercises for knee arthritis.

Fluid Drainage

If an acute and disabling amount of fluid has built up in the joint the doctor may use a syringe to drain your knee joint. While this is likely treating the symptoms and not the problem, it can provide you with some temporary relief from water on the knee.

Knee Bracing

If arthritis is the primary cause of your knee swelling and pain, an offloader knee brace may be a viable treatment option. The function of offloader knee braces is to reduce the pressure within the knee and help you stay active and pain-free. Learn more about offloader knee braces here.


  1. https://www.arthritis.org/Documents/Sections/About-Arthritis/arthritis-facts-stats-figures.pdf
  2. Chen, L. X., & Schumacher, H. R. (2008). Gout: an evidence-based review. JCR: Journal of Clinical Rheumatology, 14(5S), S55-S62.
  3. Ottaviani, S., Allard, A., Bardin, T., & Richette, P. (2011). An exploratory ultrasound study of early gout. Clinical and Experimental Rheumatology-Incl Supplements, 29(5), 816.
  4. https://www.forbes.com/2003/04/01/cx_cd_0401feat.html#2138d636d18c
  5. https://web.archive.org/web/20070505050641/http://www3.niaid.nih.gov/news/newsreleases/1999/staph.htm

Frequently Asked Questions

What is Water on the Knee?

Water on the knee refers to swelling, edema and/or joint effusion. For a variety of possible reasons, inflammation builds up in the joint causing it to become, stiff, enlarged and oftentimes painful.

What Causes Water on the Knee?

Joint swelling is a very general symptom, thus there are a number of possible causes. Swelling after a slip or fall is often associated with bruising, an irritated meniscus, or a sprained ligament. Water on the knee that occurs in the absence of any obvious trauma could be arthritis, bursitis, or in rarer cases a tumor.

What Should I Do if I Have Water on the Knee?

If you are experiencing significant and persistent joint swelling, you should consider seeing a physician or trained medical professional as soon as possible. Icing and over the counter anti-inflammatory medication can help you manage any joint swelling in the meantime.


By Simon Watts

Simon Watts is a former strength and conditioning coach with an extensive background in orthopedics and athletic therapy. He has a wealth of experience with the rehabilitation of common knee injuries such as osteoarthritis, meniscus tears, ligament injuries, and tendonitis. Simon studied Kinesiology at Dalhousie University, and as a track and field student-athlete was a national champion in the high jump and triple jump. He continues to be actively involved in the track and field community in Nova Scotia as a coach.

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