How can I convince my parents I sprained my wrist?

How can I convince my parents I sprained my wrist?
Well, as a healthcare provider, let me tell you how they convince me, (besides offering a good story). There is usually pain and swelling at the site. Sometimes bruising is present. And consistancy with pain in use and weightbearing. Without the swelling...it's difficult to convince me. And it don't have to look like a balloon, but there has to be at least some objective evidence. Without it...I'm not going to say injury didn't happen....but it determines if I give medication....or write people off work or school.
Does it sound like I get in these situations all the time?....you wouldn't believe. I'm going to start giving out my own acting awards someday. The main category will be Drug Seeker of the Year.
No offence intended in your case.
Go to your ER if you've sprained your wrist, and let them have a look at it; you may need to have it splinted to prevent further injury.
Sprain your wrist.

If it's not sprained they won't be convinced.
If it is sprained and they don't believe you, that sucks. Get a friends' parent or friend who can drive to take you to the doctor's.
Contact social services. If your parents do not believe you when you say you are injured, they will not believe you when you say you are hungry or when you say someone has raped you. Do not stay one more minute in a house like that. When parents start abusing or neglecting you, it is just the beginning and it will not get any better.