Knee Aspiration – Removing Fluid from a Knee Joint

Specialist soft tissue and joint injection physiotherapists can perform joint aspiration procedures to relieve excess fluid buildup in a swollen joint or bursa. The knee is probably the most commonly swollen joint in the body, and many patients come to see us with significant knee inflammation. This video will really help you to see what the process is like:

Can I self-refer for a Knee Aspiration?

Yes, you can. Call us on 0208 685 6930 to book an appointment with Ben Coffey (Farnborough, Hants) or Tim Allardyce (Croydon). The cost is £120.00 and includes the consultation price (£45).

Do I need an MRI Scan?

It is not necessary to have an MRI scan, but it can be useful. You are unlikely to be able to get an MRI referral from your GP if you only have joint swelling, but it is possible to pay privately for an MRI scan instead. If this is something that you wish to go ahead with, then we can arrange that for you (typical cost is around £300).

Usually, we will perform an aspiration without MRI.

What causes an excessive build up of fluid or effusion in the knee?

Knees are very prone to swelling and pain because they are weight-bearing joints. The swelling occurs when fluid builds up in or around your knee joint. This is sometimes called water on the knee but is medically called an effusion. The most common causes are:

  • Injury or trauma
  • Overuse
  • Underlying osteoarthritis

What happens before we aspirate the knee?

Before we do an aspiration, we will have a consultation (case history) with you to understand how the swelling started, what happened, how long the swelling has been present for, and enquire about other underlying medical conditions. We’ll want to know about previous knee injuries and treatments/surgeries, and what hobbies or sports you play. We’ll also want to know about things that make your knee pain or swelling worse, and things that make it better.

After the case history, we will do an examination. During this time, we might ask you to do a squat or another movement such as bending one leg. We will ask you to lie down on the treatment table so that we can assess your knee joint and feel for pockets of swelling.

We will explain the procedure in detail, so you understand more about the process and understand the very small risks involved. We will give you every opportunity to ask questions about the procedure, the risks, and benefits. If you agree and consent to have the aspiration done, then we will go ahead with the procedure.

What are the risks involved?

As with any invasive procedure, there is always a risk of infection although this is extremely rare, and we will do everything we can to ensure the procedure is aseptic and safe.

The procedure can be painful during as well as afterwards, but we will do everything we can to minimise this. It is advisable to have someone bring you to the appointment and take you home.

There is sometimes a small bleeding that occurs at the skin where the injection goes in, especially if you are on blood thinners, so it is important to ensure that your blood thinning medication is working for you (this would be in consultation with your GP).

Sometimes we inject a steroid to help settle the inflammation and prevent the joint from swelling up again and there are some risks associated with this medication:

  • Immunosuppression (steroids temporarily lower your immunity and theoretically put you at more risk of an infection).
  • Joint and soft tissue damage (this is very rare and is mainly caused by having repeated steroid injections into the same joint too often over a short time period).
  • Facial flushing and tingling (this is a fairly common reaction to steroids and is temporary lasting a few days at the most).
  • Steroids can raise your blood sugar levels, so it is important that if you are diabetic, it is a well-controlled condition.

Contraindications to aspiration

We are unable to aspirate the knee after a knee replacement.

We cannot aspirate if you have had knee surgery recently and are still under the care of orthopaedics.

Contraindications to steroid injection

  • Total knee replacement
  • Recent trauma to the joint
  • Recent or current infection
  • Recent vaccination (less that 14 days)
  • Pregnancy and breast feeding
  • Uncontrolled diabetes
  • Immunosuppression

What is actually aspirated?

In most cases, we draw out excess Synovial fluid, also known as joint fluid, is a thick liquid located between your joints. Knee joints normally have around 6ml synovial fluid. This fluid cushions the ends of bones and reduces friction when you move your joints. Inflammation of the knee can result in a significantly larger volume of fluid in the joint causing pain and reduced function. The picture below is 140ml of fluid taken from a 59-year-old woman’s right knee.

Needless to say, she felt immediate improvement! Bare in mind it's very unusual to draw out this level of fluid and we might draw out anywhere between 5ml and 30ml as a rough guide. Sometimes we aspirate blood mixed with synovial fluid. This happens after trauma to the knee, and an example can be seen on the video at the top of the page.

Very rarely, the fluid aspirated may appear infected. In this case we will advise you on seeking medical attention for further investigations.

What are the Benefits of Aspiration?

Straight away patients typically report a feeling of relief in their knee. This is usually because the excess fluid puts a lot of hydrostatic pressure on the joint. Excess fluid also reduces movement. Imagine a swollen knee and you will know that the joint will be stiff. When the fluid is removed, the knee is able to bend further. Most patients report walking significantly better following an aspiration.

Can I get this done on the NHS?

Aspiration is very hard to get done on the NHS. We've had many patients attend Accident and Emergency but not had their knee aspirated. This is because it is not a medical emergency. Rarely a GP practices may have a doctor or other clinician who specialises in soft tissue and joint injection therapy and may be able to do the procedure for you, so enquire at your surgery first.

If you have been referred to orthopaedics under the NHS, the orthopaedic consultant may elect to aspirate the knee, but there is a long wait for orthopaedics currently due to the pandemic.

What does it cost Privately?

We charge £120.00 to have a knee aspiration. This includes the consultation charge of £45.

Aspirations are done by Ben Coffey (Farnborough), Peter Tylinksi (Croydon) and Tim Allardyce (Croydon).

Does it Hurt?

In many cases, no it does not. Most patients report feeling relief when the fluid comes and out the pressure is relieved. However, we do often have to place the needle into different parts of the knee and when the needle goes into the skin, it can be uncomfortable. However, when that fluid and pressure is relieved, you'll feel a lot better straight away.