Example:

Front: Rotator cuff tear - diagnosis? Why would this make sense?

Back: MRI is generally better for soft tissue; you wouldn't use a CT scan, which is much better for bone. Remember that X-rays / CTs generally work by shooting high-frequency electromagnetic radiation "X-rays" at tissue - if the tissue has dense elements like Ca++ in bone, the X-rays will be reflected back by the dense elements. This is why X-rays and CTs are good for detecting dense things like blood (iron in heme is dense), bone (calcium is dense) or even why we use contrast (things like barium or iodide are dense elements)