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Knee Pain

Alternate Names

  • pain in the knee
  • arthralgia of the knee
  • Anterior cruciate ligament (ACL)
  • Lateral collateral ligament (LCL)
  • Medial collateral ligament (MCL)
  • Patellar dislocation
  • Posterior cruciate ligament (PCL)

Definition

The knee is the joint where the thigh bone, or femur, and shin bone, or tibia, meet. Knee pain refers to any pain or discomfort in this area of the body.

What is going on in the body?

Pain in the knee can occur for many reasons. It can be mild or severe, and involve one or both knees. Some cases of knee pain pose a serious risk of disability, especially if the person is an athlete, but do not threaten life or overall health. Some others are not serious at all. Very rarely, the condition is life-threatening.

Risks

What are the causes and risks of the condition?

There are many possible causes of knee pain, including:
  • trauma or injury, possibly producing a torn cartilage or ligament
  • overuse of the knee
  • arthritis
  • infections in or around the knee, such as septic arthritis
  • disease or infection throughout the body, which may produce generalized joint pain. Examples include sexually transmitted infections (STIs) and flu.
  • gout or pseudogout, disorders that can deposit crystals into the joint space
  • autoimmune disorders, conditions in which a person produces antibodies against his or her own body for unknown reasons. Autoimmune disorders such as rheumatoid arthritis or systemic lupus erythematosus can cause knee pain.
  • Baker's cyst, a small abnormal sac that may develop behind the knee
  • Osgood-Schlatter disease, a condition that usually occurs in teenage boys often producing a bump and the front of the leg just below the knee joint.
  • deep venous thrombosis (DVT), which is a blood clot in the leg
  • a tumor or cancer affecting the bone

Prevention

What can be done to prevent the condition?

Eating a healthy diet and avoiding alcohol can prevent some cases of knee pain due to gout. Avoiding overuse of the knees can help prevent cases from this cause. Some knee injuries can be prevented by following sports safety guidelines for children, adolescents, and adults. Many cases cannot be prevented.

Diagnosed

How is the condition diagnosed?

Often, the cause of the knee pain is obvious from the history, such as if the healthcare professional watched the person twist his body to the turf with a planted foot. A careful, systematic examination of the knee joint is important to distinguish possible injury to the various structures.
Next, x-rays of the knee are commonly taken. These can help diagnose a bone fracture, or break, and a bone tumor or cancer. Blood tests may also be ordered, such as a test called an antibody titer, if an autoimmune disorder is suspected. Other imaging tests, such as an MRI, may be done to look at the knee in more detail. If arthritis is suspected, a procedure called arthrocentesis is often done. The procedure involves inserting a needle through the skin and into the knee joint to remove a sample of joint fluid for analysis.

Long Term Effects

What are the long-term effects of the condition?

Long-term effects are related to the amount and the cause of the knee pain. An injury may cause no long-term effects at all if minor, or may cause permanent deformity of the knee. Arthritis may slowly destroy the knee joint over time. Autoimmune disorders can affect many different organs of the body. Cancer, especially bone cancer, may cause death if treatment is not successful.

Other Risks

What are the risks to others?

Most cases of knee pain are not contagious and pose no risk to others. If the cause of knee pain is an infection, such as a sexually transmitted infection or the flu, that infection may be contagious.

Treatments

What are the treatments for the condition?

For common knee pain, such as that from injury or osteoarthritis, over-the-counter pain medications are often used. Occasionally, braces and splints of various types may be helpful in resting and/or protecting the joint. If an infection is present, antibiotics may be needed.
If a serious injury occurs, surgery may be needed. Long-term arthritis may destroy a joint and require a total knee replacement. Autoimmune disorders are often treated with medications to suppress the immune system and reduce inflammation. If a tumor or cancer is the cause of pain, surgery, chemotherapy, or radiation therapy may be needed.

Side Effects

What are the side effects of the treatments?

Side effects depend on the treatments used. For instance, aspirin and antibiotics can cause stomach upset and allergic reactions. Surgery can be complicated by bleeding, infection, or a reaction to the anesthetic.

After Treatment

What happens after treatment for the condition?

Pain medication can be increased, changed, or decreased as needed. An injury often heals with treatment and needs no further monitoring. A person with a tumor or cancer may need regular monitoring for years after treatment.

Monitor

How is the condition monitored?

Those with autoimmune disorders may need repeat blood tests to help monitor their disease. Any new or worsening symptoms should be reported to the healthcare professional.

Sources

Harrison's Principles of Internal Medicine, 1998, Fauci et al.

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