Fluid on the knee, also known as water on the knee, and medically known as knee effusion or joint effusion, occurs when excess fluid accumulates in or around the knee joint. The term water on the knee is a little dated, and more commonly people refer to fluid on the knee. There are lots of reasons why you might get fluid on the knee.
Possible Causes of Fluid on the Knee and Joint Effusion
Joint effusion can result from various causes, and trauma is a common cause. If you hit your knee hard enough against something hard, there’s a good chance it will swell up. I’ve seen many swollen knees through blunt trauma. Whack it hard enough, and your knee will swell.
Injury through damage to the ligaments is another cause of knee swelling. If you tear a ligament (usually through an impact during sport, or twisting the knee badly), you’ll likely have bleeding which will cause the knee to swell. The same is true with a meniscus tear.
Infections can also provoke joint effusion, causing severe pain and swelling. Fortunately, they are not too common, but they can occur after surgery.
Osteoarthritis and rheumatoid arthritis are also common causes of knee swelling. This leads to gross restriction in range of movement of the knee. Arthritis obviously is not good for the knee joint, and degeneration of the joint is going to cause big problems. You probably want to get the swelling down.
Why Does Fluid Gather in the Knee Joint?
In most cases, it’s due to inflammation. This can be from trauma, a torn structure (ligament, meniscus) or from bursitis (swelling of a bursa, a fluid-filled sac). The knee has some space in and around the joint where fluid can accumulate. Fluid accumulating at the back of the knee is called a baker’s cyst.
Symptoms of Fluid on the Knee
Common symptoms include significant swelling around the knee joint, leading to a visibly swollen knee. Typically, one side will be noticeably bigger than the other. People will also notice stiffness, making it hard to fully extend or bend the knee. The accumulation of fluid in the knee joint often results in a feeling of tightness and is painful. When we aspirate knees, getting the fluid off the joint results in immediate pain-relief.
Occasionally we see patients come to us complaining of a swollen knee however when we look at the knee, we don’t actually see any swelling. This is often tricky to explain to a patient. I had one patient absolutely adamant that she had a swollen knee. I told her it was not swollen. I got the ultrasound scan on it, and no swelling. I advised her I was unable to aspirate the knee as there was no swelling, and she left the clinic feeling rather disappointed. However, I was quite pleased that she didn’t have swelling.
Diagnosing Fluid on the Knee
Most patients end up at either their GP surgery, or a physiotherapist. Osteopaths are also great at diagnosing it. The diagnosis is made through a combination of case history taking, and examination.
X-rays are not particularly helpful for diagnosing fluid on the knee, although they’ll certainly rule out fracture (from blunt trauma) or osteoarthritis. MRI is far more helpful, and shows the knee structures in greater detail, as well as swelling around the knee joint.
If we are worried about the content of the fluid on the knee joint, we might suggest the fluid is analysed by a laboratory. Additionally, a sample of the knee fluid might be extracted using a needle for laboratory analysis to detect signs of infection or other abnormalities.
Care and Treatment Options
Treating a swollen knee often involves a combination of care methods tailored to the underlying cause. Initial treatment often includes rest, ice, compression and elevation to reduce swelling. Icing takes quite a lot of effort – wrap the ice in a towel, don’t risk an ice burn.
We also rent Game Ready machines to patients to help them reduce swelling post-surgery, such as after a total knee replacement, or ACL reconstruction.
Medication can be prescribed to manage inflammation and pain in the joint, and physiotherapy and osteopathy may help restore knee function. Common drugs include NSAIDs (Naproxen, Ibuprofen), and painkillers are usually Co-codamol.
Preventing Fluid on the Knee
There are probably ways to prevent fluid on the knee, but that does not tend to help patients who have already got water on the knee. RICE (rest, ice, compression and elevation) can help prevent swelling from worsening. Medications may be useful, although some people do not recommend them.
We do sometimes see people come back to us after we’ve drained the knee joint. In these cases, we can use a steroid to help prevent the fluid from coming back again.
When To Call the Doctor
When your knee is swollen, red, very painful, and unremitting. You may have the start of an infection. Seek help with a medical professional, especially if you feel generally unwell or feverish. Get to A&E or ED if you are not sure. If your whole leg swells, this can be a sign of a DVT, and again, get yourself to A&E.
Final Thoughts on What is Fluid on the Knee
The fluid on the knee can be synovial fluid or blood, or a mixture of both. Usually, the fluid is a wonderful golden clear colour, sticky, and warm. The problem is that inflammation becomes chronic, leading to months of pain and soreness. If this is you, then you need to get the fluid out. If you want to get your knee aspirated, contact us and check out our pricing page.