Children usually do not have fever or other major symptoms associated with the hip pain in toxic synovitis. If xrays are taken of the hip, they are normal. The symptoms usually last for three or four days, and children get better with bedrest and ibuprofen within about a week. Most children have no further problem with the hip afterwards.
The reason that physicians get concerned when a child has this type of hip inflammation is that a more serious hip infection (septic arthritis, which needs to be treated with antibiotics), can sometimes be difficult to sort out from toxic synovitis. Most of the time children with a true septic arthritis are very sick, with high fevers, an extremely painful hip that can barely be moved, and some abnormal blood tests. Sometimes, however, it is not possible to tell the difference between the two just from the examination, and then the fluid in the joint has to be looked at. This is done by inserting a small needle into the joint and withdrawing some of the fluid. Further laboratory testing of the joint fluid can tell the difference between the two.
It sounds as though your son has recovered from his episode of toxic synovitis. It is rare but possible to have a second episode. There are no specific precautions that you need to take, other than routine visits with his primary health care provider.