Experiencing a swollen knee can be both painful and limiting, affecting your ability to move comfortably and carry out daily activities. We see patients who struggle to get out of a chair, or are unable to get up and down stairs. Sometimes we see sportspeople who report that they only get a swollen knee after playing sport. When fluid accumulates in or around the knee joint, it’s important to determine the cause to provide appropriate treatment. How is fluid on the knee diagnosed? This guide will walk you through the various methods healthcare professionals use to accurately diagnose fluid on the knee.
What is Fluid on the Knee?
Fluid on the knee, medically referred to as knee effusion, involves an excess buildup of fluid in or around the knee joint. This condition can result from numerous factors, including injuries, infections, or underlying medical conditions. The fluid exerts a hydrostatic pressure in the knee joint causing pain and stiffness.
Symptoms of Fluid on the Knee
Common symptoms of fluid on the knee include noticeable knee swelling, pain ranging from mild to severe, and a sensation of tightness within the joint. You may observe a bulge or balloon-like appearance, particularly on the front or sides of the knee, and sometimes at the back of the knee too. Other symptoms can include heat, redness, and being unable to bend your knee. As you are fully aware, this has a severe impact on living.
Clinical Examination for Fluid on the Knee
Initial Patient Assessment
The diagnostic process begins with a case history. As physiotherapists, we want to know about your medical history, including how and when your knee pain started, any aggravating factors, any sports, or any other important information that gives us an idea as to what may be wrong. We may also ask about any scans or X-rays that you had, as this will help us with a diagnosis.
Physical Examination
We need to check your knee, and we’ll bend it, straighten it, rotate it, feel it and look at it. We might look at your gait too, although in some cases, we can see when gait is not that great just by watching you walk into our room. As injecting and aspirating physiotherapists, we’ll check the knee for visible signs of swelling and inflammation. We will palpate the knee to check for tenderness and warmth and may perform some special tests on the knee. Techniques like the bulge test and fluctuation test may be used to confirm the presence of excess fluid. The examination process is normally comfortable, and takes just 2-3 minutes.
Bulge Test
The bulge test is a straightforward and painless method that physiotherapists use to check for extra fluid in the knee. During the test, we will gently press and push on different parts of your knee to move any fluid around. They start by pushing the fluid from the top part of your knee down to the main joint area. Then, they press on the outer side of your knee while watching the inner side for any small bulge or wave of fluid. If we see a bulge, it means there is extra fluid in the knee, indicating a knee joint effusion.
Fluctuation Test
The fluctuation test is another manual technique used to assess knee effusion. In this test, we place one hand on the top of the knee, just above the patella, or kneecap, and the other hand below the knee. By gently pressing down alternately with each hand, we can feel for a fluctuation or wave of fluid moving between the hands. The presence of this fluid wave suggests that there is excess joint fluid within the knee, indicating knee effusion.
Ultrasound Scan
At Croydon Physio, we might also use an ultrasound scan to take a deeper look for fluid. This is likely if we cannot see much fluid on the knee and need another view. We don’t provide reports, because we not radiologists. However, we can give you a basic understanding of how much fluid there is in the knee from the ultrasound scan.
Gait Analysis
A gait analysis involves observing how you walk and move. This is usually simply walking from one end of the room to the other two-three times. We don’t always use this, as sometimes it is quite obvious if you have a limp or gait dysfunction.
Diagnostic Imaging for Fluid on the Knee
Role of X-Rays
Most GPs will refer for an X-ray first. While x-rays primarily show bone structures, they rarely reveal too much else. However, they do show osteoarthritis of the knee which gives us a better understanding of degenerative processes happening in the knee. X-rays can identify fractures and bone masses too, although luckily these are rare. We don’t require an X-ray to have been done prior to the aspiration or injection.
MRI Scans for Fluid on the Knee
Magnetic Resonance Imaging (MRI) provides a more detailed view of the knee’s soft tissues, including ligaments, cartilage, and the synovial fluid. MRI scans are particularly useful for detecting internal damage such as ligament injuries and tears, and the extent of inflammation. Fluid is easily seen on MRI. We think this is the gold standard for knee investigation. However, we don’t need an MRI to aspirate the knee. If you have not had an MRI, don’t worry, we can aspirate or inject the knee without one.
Ultrasound Imaging
We covered this above, as we do use this clinically.
Interpreting Diagnostic Results
Radiologists provide reports on scans and imaging. We don’t provide the reports, this is usually shared with us by the patient or the scan facility. We’ll often rely on the report to give us the diagnosis rather than look in detail at the images. We may need to see the actual images, but not often, and we would inform you of this if the clinical picture is particular unclear.
Occasionally we may need to request you to see your GP for some blood tests. High white blood cell counts suggest infection, and gout can also be identified on blood tests too.
Follow-Up and Next Steps
After receiving the diagnostic results, you’ll often be frustrated that you are unable to get a clear pathway to get the fluid on your knee removed. Many patients struggle to get it done on the NHS. This is not a fault with the NHS, but it’s simply down to supply and demand, and with the current backlogs, a lot of people need treatment for all kinds of knee issues. We offer private aspirations (and injections, if needed) at an affordable price.
Key Questions for Understanding Your Diagnosis
It’s important to engage actively in your healthcare by asking your healthcare practitioner key questions about your diagnosis. Consider asking:
- Did the test results show anything abnormal?
- What are the potential causes of my knee swelling?
- Are there any further tests I should undergo?
- What are the next steps?
We often use a process called shared decision making, where we discuss the options. For example, do you want an aspiration and an injection? Or is it better to just have the aspiration? Should you go for an MRI scan after the procedure? We’ll help you answer these and discuss what are the best options for you.