Had a similar thing happen to my bitch. Went out during the day for a few runs, but when we got back and I put her away then when I went to check on her, her whole shoulder was swollen and badly bruised, I had her to the vets and they just put her on anti-inflammatories. So I bought I bio-flow collar because they're meant to help blood flow. I think it helped heal. But to this day the muscle is still soft compare to the other shoulder. And she still runs