Toxic synovitis and transient synovitis are different names for the same condition: an inflammation of synovium, tissue that is part of many body joints. The condition is caused by a viral infection. Most often, the condition involves the hip. The disorder is more common in boys and most commonly affects children 3-10 years of age. Inflammation of the synovium of the hip causes the child to cry when crawling, to limp or refuse to walk. The illness begins with a low grade fever. No specific treatment is needed. The healthcare provider may do tests to ensure the patient does not have septic arthritis, a serious bacterial infection of the joint.