About Toxic Synovitis Toxic synovitis (also known as transient synovitis) is a common cause of hip pain and limping in children. Doctors don't know its exact cause, but many kids develop it after having a viral infection (such as a cold or diarrhea).hile most kids have no long-term effects from it, some can develop toxic synovitis multiple times during childhood. If your child has a history of toxic synovitis, let your doctor know. Reviewed by: Ryan J. Brogan, DO Date reviewed: September 2014. Toxic synovitis has a scary name, but it's not a scary condition.