Suggest Treatment For Broken Tibia Medial And Fibula.

My son is 15 and broke his tibia medial and fibula. He has a fiberglass cast no weight bearing at all for 6 weeks. He did brake down into growth plate. He has been growing like crazy in past few years. I am very concerned about his growth plate? Dr. Said I he is not fealty concened about it as he probably won't grow much more? I think he still has lots of growth left, should I be concerned or get second opinion?