Toxic synovitis is a viral inflammation the hip joint. It is a very common cause of hip pain and limping in children, four to eight years old. It is also a common reason for referral to a Pediatric Orthopedist office, not because it is a serious condition, but because it must be differentiated from other conditions that are much more serious, such as a bacterial hip infection, which is a surgical emergency.
Initially, most children will complain of mild hip pain, and after a short time, possibly overnight, the child will develop a limp. Young children may refuse to walk on the effected leg at all. The child may have a low grade fever, but usually do not appear to be sick. There is often some pain when the hip is moved through a range of motion. Many times you can not notice a problem until the child tries to walk.
There is occasionally a history of mild trauma to the hip joint, but all kids this age fall and get bumped around. Often there is a history of a viral illness(runny nose, cough, a sore throat) a week or two before the onset of hip pain.
A child with a bacterial hip infection presents differently. They will appear sick looking and often have a high fever. Any hip motion, causes extreme pain. Any child with significant hip pain and a fever should be thought of having a bacterial hip infection until proven otherwise.
X-rays of the hips are taken if toxic synovitis is suspected to rule out other possible causes of hip pain. A hip ultrasound is not routinely done, but can demonstrate a hip effusion or fluid around the hip as seen in the image above. On the left side the yellow line demonstrates a hip effusion or swelling in the hip joint. Other imaging studies, such as an MRI are not needed to diagnose toxic synovitis but are occasionally needed to rule out other causes of hip pain.
The treatment for toxic synovitis is simple since the condition is self limiting, usually, lasting less then a week. Rest is the most important part of the treatment. Kids need to stay on the couch and get off their feet. This is sometimes close to impossible, but rest will decrease the hip pain quicker and allow the children to return to normal activities sooner. Non steroidal anti-inflammatory medicine such as Advil or Motrin is also helpful to decrease a childs hip pain.
The hip pain can occasionally recur, especially, if the children are too active to soon after the initial episode of toxic synovitis. The treatment remains the same for these cases.