Is a broken thumb serious? and should i keep my cast on?

Thumb fracture: You should take all fractures seriously. Be sure to listen to your physician and their recommendations. You should never remove a cast on your own. If you need your cast removed, call your physicians office to have someone trained take it off for you.

Yes and no: Any fracture is serious. Your orthopedist put you in a cast for a reason. Keep the cast on and follow up with your doctor.

Yes: To some extent, this depends on the type and location of the fracture, and whether it was open, but since the thumb is an opposable digit, it is exceedingly important to hand function. So anything you can do to optimize healing of the thumb is to your benefit. Keep your cast on until your doctor instructs you to remove it.