How do i know if i have a hairline fracture or a dislocated joint?

Xrays are a start: Thank you for your question. A dislocation of a joint is usually very apparent on an xray and is also usually associated with severe pain. A "hairline" fracture can often be seen on xray, but not always. Sometimes, if the xras are negative and clinical suspcion is high, further studies such as a bone scan, mri, or ct scan can establish the diagnosis. Thanks again, ed hellman.