Introduction:
Whenever children develop a limp they should be checked to be sure that the cause is not something that needs emergency treatment, such as septic arthritis. When the results come back, parents will often hear that the diagnosis is toxic synovitis. This sounds like bad news, but it is good news.

What is it?
Toxic synovitis of the hip is the most common form of arthritis in children. It appears suddenly, disappears suddenly, and causes no lasting problems. Thus, it is often called transient synovitis.

It typically follows viral infections, and may be caused by the body’s immune response to the virus. For this reason, it is often called postinfectious arthritis. Many viruses can lead to some type of postinfectious arthritis -- including adenovirus, chickenpox, CMV, coxsackievirus, EBV, hepatitis B, herpes, mumps, parvovirus, rubella, and smallpox.

Who gets it?
Toxic synovitis can happen in any child, but it is most common in boys between the ages of 3 and 10, after an upper respiratory tract infection.

What are the symptoms?
Boys usually complain of pain in the hip, thigh, or knee. They suddenly develop a noticeable limp. There is usually no fever, redness, or swelling of the joint.

Is it contagious?
No. The viral infections that lead to toxic synovitis are often contagious.

How long does it last?
Toxic synovitis usually disappears completely within a few days.

How is it diagnosed?
Children with a new limp usually need to be examined, have a blood test, and an imaging study to be sure there is not a condition that needs emergency treatment. In toxic synovitis, the blood tests are usually normal.

How is it treated?
Toxic synovitis needs no treatment other than pain relief.

How can it be prevented?
Usually toxic synovitis is not preventable, except by avoiding the viral infections that can trigger it.