When the pain settles post a picture or video of your son at the top of sPL/PE1. So with the scapulae protracted.
I have had a lot of patients who in this position are so weak the scapula are winging. To correct this they could only do 3x3 reps for 6-12 months. Some are so weak in the serratus anterior they can only do scapula shrugs on a bench or against the wall. I like to think of these as sPL/PE0.25 and 0.5. I get to see the extremely deconditioned on a daily basis.