This injury is really more common than people know. My son started playing again last week and so far is feeling good. He had a CT scan that showed he has fibrous healing and continues to do the exercises the PT taught him to strengthen his core and better align his back. He is playing outfield and hitting mostly every other game. He will pitch about 20-30 pitches in a game this weekend.
My son wore his brace and remained completely inactive outside of PT for 11 weeks. He went to a great PT who explained how important back alignment is and helped him really strengthen his back.
Time away from activity is crucial to healing. It was not easy for my son to watch the entire HS season from the dugout, but necessary.
Good luck to your son.