While waiting for swelling (cold hosing can help) to ease up for the ultrasound, maybe try looking into the anatomy of the shoulder instead of specifically injuries? That might help give you an idea of what structures have been insulted and possibly to what ballpark degree. Where I am not there to see how the horse moves and I am nowhere near a vet, I dare not offer more. If nothing else, it will help keep you occupied during the anxious wait. Crossing fingers and sending healing thoughts to you and your horse : )
Sure there's right and wrong but mostly there's just a whole lotta different.