Just got off the phone with my son the Marine.
First, OM, they only cut open L4 for the operation and they put the bone piece back in. The Lt. Commander Doc said at his age it'll fuse up fast. Pretty much what you said.
Second, they didn't feel they needed to fuse the vertebrae, so he should have much more "motion" than expected, almost "normal". I take this as VERY good news.
Third, they said that if he hadn't had the tumor, then when the disk popped out it wouldn't have hurt and he would have only had a couple of weeks of back pain and then been back at work. It was because the popped disk didn't have anywhere to go (because of the tumor) that he had pain etc... so the popped disk really did save my Marine from some bad stuff down he line. (I know I'm looking on the bright side.) If he hadn't popped the disk he would have eventually had nerve damage from the tumor which would not have been repairable.
Finally, I told my Marine that he was one lucky Jar-Head to have popped a disk, discovered a tumor that would could have caused trouble down the road, and managed to get Uncle Sam to pay for it all. "Well done." He just laughed weakly, given all the pain meds he's on now.
He sounded like he'll be headed up to lay around at out place in a few weeks, and his lovely girlfriend is doing a great job of taking care of him.
I'm a much more relaxed Dad now...
Thank you all for your good wishes and a special THANKS to OM for his help and council.
Cheers, I'm going to have a large glass of Tequila.
Beau