A swollen knee…
It is a common concern. First things first – What are we talking about when we say a “swollen knee”? As far as most joints are concerned, swelling outside the joint and swelling inside the joint have different meanings to your doctor because they imply different potential diagnoses. For this post, I will be discussing the swelling inside your knee only. You may know it better as “water on the knee.” We’ll leave a discussion about swelling outside your knee for another day.
What Is It?
Swelling inside your knee can result from one of two types of fluids. When the swelling is the result of a nontraumatic cause, the fluid in your knee is called an “effusion.” Different disorders and even different degrees of the same disorder can have varying amounts of knee effusions. With that said, it is actually normal to have some fluid in your knee. This fluid is synovial fluid. The lining of your knee is responsible for producing it. It is vital for a healthy, well-functioning joint. Think of it as oil for your car’s engine. However, when the amount of this fluid is excessive, it is no longer normal but rather a sign of a problem in your knee.
When the fluid in your knee is from a traumatic event, it may be either an effusion or a “hemarthrosis”. A hemarthrosis simply means that there is blood in your joint. A hemarthrosis is never normal.
What Are The Symptoms?
Your knee can accept small amounts of fluid without causing any symptoms. However, when the amount of fluid is too much, symptoms often result. Commonly, there is a noticeable enlargement of your knee as well as some loss of motion. Frequently, this is accompanied by pain, most often in the back of your knee or above your knee cap. This pain is particularly noticeable when bending your knee.
The following video ilustrates two simple ways to determine if you have a small amount of fluid in your knee…
Why Do I Have A Swollen Knee?
Usually, swelling in your knee comes from one of three types of problems. So although it may not be pleasant for you, identifying a swollen knee may be very helpful to your doctor in diagnosing your problem. The three most common causes of a swollen knee are:
1. Trauma
Nearly any type of trauma can cause a swollen knee. The most common injuries that cause swelling in the knee are ligament injuries such as an ACL tear, fractures (breaks in the bone), and bone bruises. Bone bruises can occur from an external force contacting a knee bone or more commonly from two of your bones banging against one another, as may happen when your knee cap dislocates.
Having swelling doesn’t determine the posttraumatic diagnosis by itself, but if there is no recollected trauma, then its absence helps narrow the determination to the next two potential causes I’m going to discuss. Of course, if there was trauma, then your history, physical exam and available imaging studies will help determine the correct diagnosis. Swelling from trauma often resolves in 4-6 weeks. The underlying problem, however, may continue to be an issue depending on what the problem is and how significant it is.
2. Meniscal Tears
The menisci are small c-shaped rubbery discs in your knee that rest between the end of your thighbone (femur) and upper shin bone (tibia). They help provide stability, cushioning and normal functioning of your knee. At times these can tear. Frequently, these tears will cause pain in your knee. They may also result in a swollen knee. Usually, meniscal tears cause lesser amounts of knee swelling. However, larger tears, for instance, displaced bucket handle tears, may cause greater amounts of fluid in your knee. This swelling will usually persist until the tear is treated
3. Cartilage Issues
There are a number of cartilage issue that can cause a swollen knee. Osteoarthritis is by far the most common. Osteoarthritis (OA) is a degenerative process of our joints. It leads to a loss of cartilage, bone changes at the joint surfaces, and a release of inflammatory and degenerative mediators throughout the joint. The common symptoms of OA are pain, stiffness, weakness, clicking or catching, giving way, and swelling. Cartilage issues, including OA, can cause greater degrees of swelling inside the knee than other sources of knee swelling. This swelling can occur from loose pieces of cartilage floating around the knee, exposed bone from the loss of cartilage overlying the joint surfaces and those mediators mentioned above.
Additional cartilage issues that may also cause knee swelling are inflammatory forms of arthritis, such as rheumatoid arthritis and Lyme arthritis, as well as chondral defects (focal areas of cartilage loss).
The takeaway…
When you have a swollen knee, it can cause pain, stiffness and a sense of “tightness.” it often can and should cause concern. Swelling in the knee always means something is wrong. Although the swelling helps narrow the potential diagnoses, it will likely take a doctor’s evaluation to make a final determination and definitely will require a doctor’s expertise to institute a treatment plan.