Your son had got operated for strangulated hernia
. And almost 10 days got over. If the patient was having hernia for long duration then there might be thickening of the hernia sac ( not testicle sac) and there will be lot of adhesions between the sac and the surrounding structures. So a lot of dissection will be required during surgery which can result in swelling of the scrotum
(testicle sac). In your case its a strangulated hernia. So there will be lot of inflammation and edema of the surrounding structures due to which he had this swollen testicle sac. Don't worry about this problem. Usually the swelling will reduce in size after 1 month. No specific treatment is necessary. Just ask him to wear a tight underwear or some scrotal support.