Thank you everyone. We spoke to the surgeon who said that surgery to repair the leg can be done. She said that this kind of fracture is not common and tricky to repair. Because the break is so close to the joint they have to attach either pins or a metal plate and screws to the growth plate. They will not know which until they are able to open the leg up and see what is happening inside.
Since they are attaching it to the growth plate the surgeon mentioned the leg may not continue to grow and he could end up with a limp in that leg. However since he is already 5 months and 4.4 pounds he doesn't have a lot of growth left (growth charts put him at his adult weight of 5.5 lbs.)
We were told the first 6 weeks of recovery is crucial that he not jump and have very limited walking. If the repair doesn't go well after 6 weeks they will have to do an amputation.
This makes me so concerned that he may go through this huge surgery today and an intense recovery, just to be told we have to amputate it.