I need help with creating a fake surgery name. Help!?

My son is getting a prosthetic testicle surgery. He lost one when he was a toddler and is now a teen. He's been wanting this for years. Thing is no one knows about his condition and he wants it to remain that way! So he needs to tell people a reason he's getting surgery and going to be out of school and action for awhile. Something at the top of the leg-that would work in maybe with a sports injury?? He plays all sports. Something not serious, but would account for him walking a little carefully when he starts back to school. Any ideas?