Experiencing knee pain and swelling can be both uncomfortable and worryingly chronic. When you visit your GP, one of the key diagnostic tools they might use is an x-ray to check for any underlying structural damage to the knee. But is an X-ray actually useful? Let's explore the process and importance of fluid on the knee x-ray diagnosis and other essential examinations.
What is Fluid on the Knee?
Simply put, this is having a swollen knee from fluid accumulation. X-rays of the knee can help identify the underlying issues causing this effusion, providing a clear view of any abnormalities within the joint such as osteoarthritis.
Common Causes of Knee Fluid
There are several potential causes of fluid in the knee, ranging from acute injuries to chronic conditions. Common causes include arthritis, which leads to joint inflammation and degeneration, and injuries such as meniscal tears or ligament damage. Conditions like gout and infections such as septic arthritis can also result in fluid accumulation. In some cases, cysts like a Baker cyst may form, contributing to knee swelling. Many of these conditions we won’t see on X-ray, but they are diagnosed by MRI or physical examination.
Symptoms Associated with Fluid on the Knee
Let’s make this simple, if you have fluid on the knee, it’s likely you will have knee pain and stiffness. You’ll find walking uncomfortable, and you may be unable to kneel or put weight through the knee joint on kneeling. You’ll probably be unable to exercise, and you may limp as gait is often affected.
Diagnosing Fluid on the Knee
Sometimes having fluid on the knee or excess swelling is benign, meaning it’s just there for no apparent reason. Sometimes it’s there due to impact or trauma (the fluid in this case is often blood). Sometimes the fluid is there due to a tear, like a ligament or meniscus tear (common). Sometimes there’s swelling due to arthritis. We’ll help drill down what could be the underlying issue.
Imaging Techniques for Diagnosing Knee Fluid
Role of X-Rays in Diagnosing Knee Fluid
X-rays simply show us the knee bones and the knee joint. It won’t show us the ligaments, the menisci, the tendons, and in many cases it won’t show the fluid.
Comparing X-Ray with Other Imaging Methods
X-rays are quick, cheap, easily available on the NHS, but the disadvantage is the radiation. MRIs show more detail, but they are more expensive, and much harder to get on the NHS. One great way to check for fluid on the knee is via an ultrasound scan at the time of the consultation prior to having your knee aspirated.
Interpreting X-Ray Results
X-rays are read by radiologists, who will report on the X-ray and the findings and these are usually sent to your GP.
MRIs are also reported by a radiologist, and are usually sent to your GP if they MRI was performed on the NHS. If the MRI was private, then the report is sent to the referring clinician. You can request a copy of the report at any time by calling the MRI centre who performed the scan.
Aspiration
Once you determine there’s fluid on the knee, you’ll probably want to get it out. In some cases, it just disappears on its own. In some cases, it will respond to ice and elevation. However, sometimes it just sticks around and this is when you are most likely to need an aspiration.