Fluid on the Knee, also known as a knee effusion or “water on the knee,” is a painful condition resulting from the buildup of fluid in and around the knee joint. Generally, we treat fluid on the Knee with simple strategies such as ice, medication, and a compression wrap. However, sometimes we must drain fluid from the Knee, also known as a knee joint aspiration. So, how do you perform knee drainage, and when is it appropriate to do so?  

Causes of fluid on the Knee

The knee joint is a synovial joint lined by synovium, which produces synovial fluid. This fluid protects the cartilage lining the joint surface and reduces friction with joint movement. However, when the joint becomes diseased, it has excess synovial fluid. Common causes of excess knee fluid include osteoarthritis, inflammatory arthritis, infection, or traumatic injuries such as meniscal or cruciate ligament tears. Rare causes include tumours such as pigmented villonodular synovitis. 

Knee Aspiration: Why Do We Perform a Knee Drainage? 

We drain fluid from the Knee for two reasons:

  • You want to determine the cause of the water on the Knee, i.e., for diagnostic purposes.
  • You want to help reduce the swelling, especially when simple measures such as ice and ibuprofen are ineffective. A buildup of knee fluid more significant than 50 ml often causes pain and restricts mobility. Draining the Knee can ease the symptoms.

Can You Diagnose Knee Diseases from Knee Aspiration?

Yes. Knee effusions are not all the same. Fluid in the Knee caused by trauma, such as a meniscal tear, differs from fluid from inflammatory arthritis, such as gout.

When we drain the Knee, we send the fluid to a laboratory for analysis to determine the types of cells present. Microbiologists also look for bacteria or crystals in the fluid, which can point to the cause. We use this information in conjunction with X-rays, MRI scans, and blood tests to confirm the cause.

How to Get Fluid Out of Knee?

picture of arthroasmid injected into knee joint with ultrasound-guidance

Ususally, we perform a knee aspiration in a clean clinic room. Generally, we target the top part of the knee joint just above the patella.

First, we clean the area with antiseptic. Second, we use a needle to puncture the skin to get to the knee joint. Using ultrasound to direct the needle into the joint improves accuracy. Additionally, ultrasound enables us to drain the knee of fluid. Finally, we place a bandage on the puncture site to prevent bleeding from the skin. The entire process can take a few minutes.

Sometimes, when fluid accumulation in the knee is due to inflammation or an injury, we inject cortisone or other injectables, such as hyaluronic acid or platelet-rich plasma. Additionally, we recommend applying regular ice and a compression bandage to help prevent the knee effusion from returning.  

Risks of knee drainage

Generally, the procedure is low-risk, mainly if performed in a clean room and with ultrasound guidance. However, there is a small risk of the knee joint returning or introducing infection. Additionally, superficial swelling and skin bruising may occur at the entry site.

Does Draining Fluid from the Knee Hurt?

Generally no. You may feel slight pain or discomfort as the needle enters the joint. However, removing the fluid from the knee should not be painful. Additionally, using ultrasound enhances the accuracy of needle placement and minimises procedure discomfort.

If we analyse the fluid on the knee, we’ll need to speak to you after a few days.

What to Do After a Knee Joint Aspiration?

The steps after a knee aspiration are essential. First, leave the bandage in place until your doctor instructs you to remove it. You should keep the entry site clean. Second, you can return to normal activities after the procedure, but you should avoid resuming sports or walking longer distances until you’re cleared to do so. Finally, if the knee is sore, ice it and take ibuprofen or NSAIDS every 4-6 hours until the pain subsides.

Other Frequently Asked Questions about Knee Aspiration:

What are the different ways to reduce fluid in the knee? 

Simple measures to control water on the knee include the following:

  • Regular ice packs for 10 minutes every 4-6 hours
  • Using a compression bandage to apply pressure to the joint
  • NSAIDs such as ibuprofen or diclofenac
  • Wearing a knee brace for walking or sports

Can a knee effusion return? 

Yes. Fluid on the knee can return after days or weeks. The key is to identify the cause so that the treatment can be more effective and prevent it from returning.

A Final Word from Sportdoctorlondon about Knee Aspiration

Knee drainage is an effective technique to aid in diagnosis and alleviate symptoms associated with knee fluid accumulation. You should consult an experienced doctor who can perform this procedure efficiently, preferably with the aid of an ultrasound to enhance its effectiveness.

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