[Highland Park] pediatric orthopaedist?

My ten-year-old son badly fractured his upper arm about seven weeks ago and unfortunately is not healing as expected. We like the orthopaedic surgeon who did his surgery very much, but if the bone is still not healing when we go back to Children's in early October, out of caution we will want to seek a second opinion. Given that it can often take a long time to get an appointment with top docs, I thought it might be a good idea to start looking now. Does anyone have a recommendation for a great pediatric orthopaedist who might have expertise in delayed union and/or nonunion?