Water on the knee

Overview

Water on the knee is a general term used to describe excess fluid that accumulates in or around your knee joint. Your doctor may refer to this condition as a knee "effusion." Painful knee effusions may be the result of trauma, overuse injuries or an underlying disease or condition.

The most common cause of water on the knee is osteoarthritis. Osteoarthritis is characterized by the breakdown of joint cartilage and may affect any joint in your body, including your hips, knees, lower back and feet.

The type of fluid that builds up in your knee depends on the underlying disease, condition or type of traumatic injury that causes excess fluid to build up. This joint (synovial) fluid may contain irritating crystals, bacteria or blood.

The pain and swelling associated with water on the knee don't have to limit your mobility. Once your doctor determines the cause of this condition, he or she can recommend self-care measures and treatment to keep you on the move.

Signs and symptoms

Signs and symptoms of water on the knee depend on the cause of excess fluid buildup in the knee joint. These may include:

• Pain. With osteoarthritis, pain occurs when bearing weight on your knees. The pain typically subsides with rest.
• Swelling. One knee may appear larger than the other. Puffiness around the bony parts of your knee appears prominent when compared with your other knee.
• Stiffness. When your knee joint contains excess fluid, your range of motion may be limited. In other words, you can't bend or straighten your knee as far as you normally can.
• Bruising. If you've injured your knee, you may note bruising on the front, sides or behind your knee. Bearing weight on your knee joint may be impossible and the pain unbearable.

Causes

Your knee is the most complex joint in your body. It functions like a hinge, allowing your knee to bend and straighten. Damage to any part of your knee can cause the painful build up of excess joint fluid. Examples of traumatic injuries that cause fluid buildup in and around the knee joint are:

• Broken bones (fractures)
• Meniscus tear
• Ligament tear
• Overuse injuries

Underlying diseases and conditions that may produce fluid buildup in and around the knee joint include:

• Osteoarthritis
• Rheumatoid arthritis
• Infection
• Gout
• Pseudogout
• Kneecap (prepatellar) bursitis
• Cysts
• Tumors

The medial and lateral meniscus function as shock-absorbing cartilage in your knee joint. A tear to the meniscal cartilage can cause water on the knee.

Two of the four ligaments that connect the thighbone (femur) to the shinbone (tibia) are the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). The ACL and PCL crisscross one another as they join these leg bones together. A tear in either of these ligaments can cause excess fluid buildup in your knee joint.

Risk factors

Having osteoarthritis or engaging in high-risk sports that involve rapid cut-and-run movements of the knee — football or tennis, for example — means you're more likely to develop water on the knee.

If you're overweight or obese, your body places more weight on the knee joint when you walk. This causes more wear and tear on your knee joint. Over time, your body will produce excess joint fluid.

When to seek medical advice

Having water on the knee because of an underlying condition doesn't need to limit your mobility or decrease your quality of life. See your doctor promptly if:

• You injure your knee.
• Self-care measures or prescribed medications don't relieve the pain and swelling.
• One knee becomes red and feels warm to the touch as compared to your other knee.

Screening and diagnosis

Your doctor will examine your knee thoroughly and may recommend diagnostic tests. If the underlying cause of water on the knee is unknown, he or she will want to know why you've developed this condition.

Diagnostic tests include:

• X-ray. Your doctor will request an X-ray to make sure you haven't broken or dislocated any bones or to determine if you have arthritis.
• Magnetic resonance imaging (MRI). This test detects abnormalities of the bone or knee joint, such as a tear in your ligaments, tendons or cartilage.
• Joint aspiration (arthrocentesis). During this procedure your doctor withdraws fluid from inside your knee for analysis such as cell count, culture for bacteria, and examination for crystals such as uric acid or calcium pyrophosphate dihydrate (CPPD) crystals found in gout or pseudogout.
• Blood tests. If your knee is swollen, red and warm to the touch when compared to your other knee, your doctor may be concerned about inflammation due to rheumatoid arthritis or a crystalline arthritis such as gout or pseudogout, or joint infection. Besides sending the joint fluid to the lab for analysis, he or she may request blood tests to determine your white blood cell count, erythrocyte sedimentation rate, and perhaps the level of C-reactive protein or uric acid.

Complications

Water on the knee can severely limit the mobility of your knee joint if left untreated. If your knee joint is infected, it may cause destruction of the joint or it may extend into the bone (osteomyelitis).

Treatment

Treatment of water on the knee focuses on treating the underlying disease or injury.

• Osteoarthritis. Removing fluid from your knee joint can help relieve the pressure of joint fluid buildup. After aspirating joint fluid, your doctor may inject a corticosteroid into the joint to treat inflammation.
• Gout or pseudogout. With these two conditions, uric acid or CPPD crystals deposit in joints and may cause inflammation in the joint and surrounding soft tissues. An intra-articular corticosteroid injection, nonsteroidal anti-inflammatory drugs (NSAIDs) (Motrin, Advil, others), or colchicine may be recommended for treatment of an acute attack of gout or pseudogout. Allopurinol may be started after an acute attack of gout has subsided. This medication decreases the body's production of uric acid in an attempt to prevent additional episodes of gout.
• Infection. Your doctor will prescribe antibiotics to treat the underlying infection. You may need repeated aspiration of the infected joint or surgery.
• Arthroscopic knee surgery. Using an arthroscope — a surgical tool designed to look inside your knee joint — an orthopedic surgeon examines the inside of your knee joint for wear and tear. The surgeon also may repair damage inside your knee joint with this instrument.
• Joint replacement. According to the American Academy of Orthopaedic Surgeons, only one of four people with osteoarthritis of the knee will require surgery. But if bearing weight on your knee joint becomes intolerable, your doctor may refer you to an orthopedic surgeon for knee replacement.

Prevention

Water on the knee is typically the result of a chronic health condition or traumatic injury. To prevent water on the knee, work with your doctor and other members of your health care team to manage the condition or traumatic injury that causes it. Avoiding trauma isn't always possible, but you can take safety measures — such as wearing a brace your doctor or physical therapist prescribes to protect your knee joint during physical activity.

To avoid water on the knee:

• See your doctor regularly. See your doctor regularly if you have a chronic health condition such as osteoarthritis, rheumatoid arthritis or gout.
• Follow through on your doctor's orders. Take the medications your doctor prescribes to treat the underlying disease or condition that causes water on the knee. If your doctor, physical therapist or sports trainer recommends you wear a knee brace because of a prior injury, be sure to follow through.
• Be gentle with your knees. If you're overweight or obese and plan to start an aerobic exercise program as part of a weight-loss program, avoid excess wear and tear on your knees. Select an aerobic activity that doesn't place continuous weight-bearing stress on your knee joints, such as water aerobics or swimming.

Self-care

Taking care of yourself when you have water on the knee includes:

• Rest. Avoid weight-bearing activities as much as possible when your knee is painful and swollen.
• Ice and elevation. Cold therapy can help control pain and swelling. Apply ice to your knee for 15 to 20 minutes every two to four hours. You may use a bag of ice, frozen vegetables, or an iced towel cooled down in your freezer. When you ice your knee, raise your knee higher than the level of your heart, using pillows for comfort.
• Pain medication. Acetaminophen (Tylenol, others) is often effective at relieving pain. Nonsteroidal anti-inflammatory drugs, or NSAIDs, (Advil, Motrin, others) are effective for relieving pain and inflammation. If these don't relieve the pain, ask your doctor about prescription medications.
• Muscle toning exercises. If your thigh (quadriceps) muscle or hamstring muscles are weak, your doctor may refer you to a physical therapist to learn how to strengthen these muscles to better support your knee.
• Managing your weight. Losing weight will minimize the amount of weight your knees have to support when you engage in weight-bearing activities.

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