How do you know if bursitis to diagnosed correctly?

Bursitis: Bursitis can usually be diagnosed by just touching/pressing on the place where a bursa normally overlies a joint. There will be consistent tenderness there, and either you or a friend can demonstrate this until it resolves. It is usually due to overuse, so cutting down the load should relieve it over several weeks. When it doesn't settle down, suspect some other injury to the joint or bone.

MRI or US: Most of the time bursitis can be diagnosed from the history or physical examination. If imaging is needed for further evaluation the MRI or ultrasound are the best examinations. An x-ray is also useful to look for calcification in the bursa.