Transient synovitis of the hip, also called toxic synovitis, is the swelling and inflammation of the tissues surrounding the hip joint, states American Academy of Family Physicians. Usually this condition only affects one hip at a time. Toxic synovitis is the most common cause of hip pain in children, typically afflicting those between the age of 3 and 10. It is more likely to occur in boys than girls. It is called transient because it is usually a short-lived condition.
Transient synovitis of the hip may emerge shortly after a viral infection, and sometimes a low grade fever accompanies it. Some doctors believe that the immune response to an illness causes the condition, according to KidsHealth. Children who are experiencing this condition may limp, walk with their toes turned outward or walk on their tiptoes in an effort to mitigate the discomfort, or they may refuse to walk entirely. When babies have this condition, they may crawl abnormally and cry more than usual during diaper changes and other situations that involve displacement of the hip joint. Sometimes toxic synovitis is confused for a more serious affliction known as septic arthritis, a condition in which bacteria enters the joint tissues and potentially causes permanent damage.