Effusion means collection of fluid, simple term swelling. It is an internal swelling which has developed because of trauma to the joint. See an experienced therapist or orthopedic surgeon to check if there is any laxity of tissues or structural damage to the shoulder soft tissue, if that is not seen on MRI possibility is low, in that case you'll have to strengthen your shoulder cuff muscles..
Health Tips
Avoid sleeping on affected side.
Do not take massage.
Apply ice packs to reduce swelling and pain.