Hurt hand. had xray 2 days after and 10 days after, both came back normal. could a hairline fracure still have been missed?

Unlikely...: It is quite possible for a subtle hairline fracture not to be visible on an initial X-ray. However, they are usually seen on follow up X-rays 10 days later because of evidence of healing. If you have normal bone density (ie. no osteoporosis), your chances of having a fracture are unlikely. If you have persistent pain, your doc may order an MRI which will show even subtle fractures.