Toxic synovitis is a frequent cause of limping with hip pain in children. It occurs in children prior to the onset of puberty and is a transient arthritis of the hip that usually resolves on its own. Its cause in not known but boys are affected more frequently than girls (approximately 4 to 1).

Symptoms are usually mild and generally include hip pain and a slight limp. The hip pain almost always involves only one side (unilateral). A low grade fever (usually less than 101 degrees) may be an early symptom. Aside from the hip discomfort, the child does not usually appear ill.

Toxic synovitis is a diagnosis of exclusion, which means that it is diagnosed when other, more serious conditions, have been ruled out. In children there are three potentially serious diseases that can cause hip pain and limp: septic hip, slipped capital femoral epiphysis, and Legg-Calve-Perthes disease. Once these other diagnoses have been excluded, then the diagnosis of toxic synovitis (which is the most common of all these diseases) is usually made.

• hip pain (on one side only)
• limp
• thigh pain, in front and toward the middle (may be present)
• knee pain (may be present)
• low grade fever, less than 101 degrees Fahrenheit (may be present)

• ultrasound of the hip will demonstrate a joint effusion
• X-ray of the hip (expected to be normal)
• ESR may be slightly elevated
• complete blood count (may show increased white cells)

• aspiration of fluid from the hip joint
• bone scan
• MRI