Welcome to HealthcareMagic forum.
As per your query, you son had open reduction and internal fixation
for an elbow fracture
done with plates and screws. Such kind of fractures
heal by primary and secondary healing which should be completed in a year and half.
As the surgery was one 2 years ago, you can visit his orthopedic and plan to remove the plates and screws. There shouldn't be any problem with the fractured bone and his growth can also occur normally.
Do visit his orthopedic as and when possible.
Hope this helps.