What Is Joint Effusion?
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Joint effusion, commonly referred to as water on the knee or fluid on the knee, is the abnormal accumulation of fluid in or around a joint. It is most commonly caused by infection, injury, and arthritis. In addition to swelling, joint effusion is associated with pain and stiffness. The knee is the joint most commonly affected by effusion, although it can occur in the ankle, elbow, shoulder, and hip.
The term effusion can also be applied separately to the accumulation of the fluid in the lining of the lungs, called a pleural effusion.
An effusion should not be confused with edema. Edema is the generalized swelling of tissues caused by inflammation, allergy, heart failure, and other conditions. Effusion, by contrast, specifically describes the swelling of a joint.
Symptoms
While the symptoms of joint effusion are similar whatever the underlying cause, the characteristics, and severity can vary significantly. The classic symptoms of joint effusion are:1
Swelling, ranging from a mild, generalized puffiness to severe swelling and inflammation
Pain, ranging from a dull throb to sharp, immobilizing pain
Stiffness, which can limit a joint's range of motion or entirely immobilize a joint
Redness and warmth, associated with localized inflammation
Joint effusion caused by an injury may be accompanied by bruising and bleeding in the joint space. Joint infections will often manifest with generalized symptoms such as fever, chills, malaise, and weakness. Joint effusion associated with severe arthritis may lead to progressive muscle loss, a condition referred to as arthrogenic muscle inhibition.
A common complication of a joint effusion is the formation of the fluid-filled nodule, known as a Baker's cyst, in the joint space.2 It is caused when the amount of joint fluid is so excessive that it cannot be reabsorbed by the body. While a smaller Baker's cyst may not cause symptoms, larger ones can sometimes be felt and cause pain with movement.
Causes
Joint effusion can be broadly classified as either septic (caused by infection) or aseptic (not caused by infection). Infectious causes are typically referred to as septic arthritis. Aseptic causes may be categorized as either injuries or arthritis.
Septic Arthritis
Septic arthritis, also known as infectious arthritis, is most commonly caused by bacteria.3
When caused by an infection, the onset of symptoms is usually rapid and intensely felt. Within the context of a joint infection, an effusion is usually extremely painful, particularly with movement.
The joint infection may be caused by a systemic infection that has traveled through the bloodstream. Alternately, bacteria may have been introduced into a joint by a penetrating wound or a medical procedure. Some of the factors that can increase the risk of septic arthritis include:
Older age
Diabetes
HIV
Intravenous drug use
Joint replacement
Recent joint surgery
Arthritis
Fungal, viral, and parasitic causes are most commonly associated with a compromised immune system, such as in people with advanced HIV infection, organ transplant recipients, or those undergoing cancer chemotherapy.
Joint Injury
A sports injury is a common cause of joint effusion, especially of the knee.4 A car accident, serious fall, or blunt force impact can also lead to an effusion. The injury may involve bone, connective tissues (such as tendons and ligaments), or joint cartilage (meniscus). Pain, swelling, stiffness, and difficulty extending or rotating the joint are common.
In addition to a traumatic injury, joint effusion may result from a repetitive stress injury.5 This is the type that occurs after repeating a movement again and again, usually in connection with an occupation or a sports activity. Effusion tends to affect the larger joints such as the knee, shoulder, elbow, or ankle.
Within the context of repetitive stress injuries, effusion occurs most commonly with bursitis (the inflammation of the fluid-filled sac which cushions a joint) and tenosynovitis (inflammation of the tendon sheath where a muscle attaches to a bone).
Arthritis
Joint effusion is a common feature of arthritis associated with either chronic inflammation or an acute bout of joint inflammation. Inflammation, as a rule, manifests with edema and the dilation of blood vessels under the influence of the immune system.
While this is meant to provide larger immune cells access to the site of an injury, severe or persistent inflammation can lead to the accumulation of more fluid that the body can absorb. Effusion is the consequence.
Generally speaking, there are two types of arthritis:
Osteoarthritis, also known as "wear-and-tear" arthritis
Autoimmune arthritis, such as rheumatoid arthritis, gout, juvenile idiopathic arthritis, and psoriatic arthritis, in which the immune system directly or indirectly attacks joint tissues
With osteoarthritis, joint effusion primarily affects the knee and is most commonly associated with extensive joint damage. With autoimmune arthritis, joint effusion may be associated with either chronic inflammation or the acute flare-ups (known as attacks or exacerbation).
ttacks are especially common with gout, an autoimmune disorder characterized by the accumulation of uric acid crystals in the joint space (mostly the big toe).6 The appearance of gout symptoms is often so rapid and severe that joint effusion is a natural consequence.
Diagnosis
The diagnosis of a joint effusion may involve a physical exam, imaging tests, and lab evaluation of joint fluids.7 In addition, the doctor will review your medical history, current health, and co-occurring symptoms to arrive at a diagnosis.
Physical Examination
The physical exam, in which the doctor will touch (palpate) and manipulate the joint, can reveal a lot about the underlying cause of the condition. For example:
With arthritis, the lubricating tissue between the joints, called the synovium, will feel boggy. Moreover, with the exception of gout, the swelling will be gradual rather than swift.
Joint infections tend to develop rapidly and cause excessive pain and redness.
Acute swelling accompanied by the inability to bear weight may suggest a torn ligament or fracture of the knee.
Imaging Tests
Following the physical exam, imaging tests may be ordered to determine the exact cause of the effusion. Each test has its benefits and limitations:
Ultrasonography uses sound waves to visualize bone and connective tissues. It can be used to confirm arthritis or the inflammation of tendons or ligaments. While non-invasive and portable, an ultrasound poses a disadvantage as it is less able to visualize soft tissues than other forms of imaging.
X-rays and computed tomography (CT), both of which expose you to ionizing radiation, are best suited for diagnosing and characterizing bone fractures and arthritis.
Magnetic resonance imaging (MRI), which utilizes magnetic fields and radio waves, is able to visualize soft tissue, cartilage, and joint structures that the other tests can't. On the downside, the procedure can be costly and will sometimes involve the use of intravenous contrast agent.
Joint Fluid Analysis
In the course of diagnosing your condition, your doctor may want to drain (aspirate) fluid from the joint space, known as synovial fluid, to help alleviate pressure and pain. The procedure, referred to arthrocentesis, may also be used to obtain a fluid sample for evaluation in the lab.8
Synovial fluid will usually be clear and have the viscosity of an egg white. Any changes in its appearance, texture, and cellular composition can provide clues as to the underlying cause of joint effusion.
Some examples of tip-offs the synovial fluid can provide include:9
Cloudy fluid may suggest rheumatoid arthritis due to inflammatory increases in white blood cells (generally over 10,000 per cubic millimeters).
Yellow-green fluid may suggest an infection, particularly if the white blood cell count (WBC) is greater than 20,000 per cubic millimeter. Traces of pus may also be seen.
Golden fluid is commonly associated with gout. Microscopic examination may also reveal needle-like uric acid crystals.
Bloody or pink fluid is the classic sign of a joint injury.
Clear fluid is typically seen with osteoarthritis since it doesn't involve any inflammation. The WBC will usually be below 2,000.
If an infection is suspected, the lab may also perform a culture to grow and isolate the offending bacteria or fungus.
Treatment
Whatever the underlying cause, the standard treatment of a joint effusion includes rest, ice application, immobilization, and a nonsteroidal anti-inflammatory drug (NSAID) like Advil (ibuprofen) or Aleve (naproxen).10
In some cases, arthrocentesis may be used therapeutically if the swelling is especially severe. This may be followed by an intra-articular corticosteroid injection to quickly reduce pain and inflammation, particularly if there is a severe injury or arthritic joint damage.11
Infections can usually be treated with a 14-day course of a broad-spectrum oral antibiotic such as ciprofloxacin. Other more serious types, like those caused by systemic gonorrhea or methicillin-resistant Staphylococcus aureus (MRSA), may require between a two- and four-week course of intravenous antibiotics.
Steps may also be taken to better control rheumatoid arthritis and other forms of autoimmune arthritis. This may involve the use of immune-suppressive drugs, like methotrexate and Humira (adalimumab), aimed at tempering the abnormal immune response.
Arthroplasty (joint surgery) is reserved for serious joint injuries or to repair joints immobilized by arthritis.12 Severe cases may require joint replacement.
Prevention
While joint effusion can’t always be avoided, there are things you can do to significantly lower your risk:13
Lose weight, if needed, to reduce stress on the hips and lower extremities.
Embark on a low-impact exercise plan if you're experiencing pain in the knee, hip, or ankle. Avoid heavy weightlifting or deep squats.
Use resistance training to strengthen muscles in and around your joint. This may include using a leg extension machine for the knees or resistance band training for the shoulder and rotator cuff.
Perform gentle knee and shoulder stretches before exercise or throughout the day if you're sitting at a desk for a long period of time.
Use an elastic knee support or elbow brace when engaging in contact sports or manual labor.
Never exceed your physical capabilities, especially as you get older. This may involve changing the types of sports you engage in (such as switching from running to cycling).
Don't strain to reach for something. Use a stool for hard-to-reach items.
Listen to your body. If you experience any acute or persistent joint pain, get it checked by a doctor sooner rather than later
