My doctors found my leg bone in my fibula had a strange shape to the top of it like a ball was growing inside my bone. Theyve ordered a mri. Worried!?

Bone growth. The description is probably indicating expansion of the proximal fibula. This can be caused by benign processes such as cyst, tumor, or posttraumatic lesion. Sometimes the expansion represents malignant tumor (cartilage, bone, fibrous tissue etc). Age of patient is noted.Depending on the interpretation of the xray image and mr imaging, the process could represent either benign or malignant process.
Results. You need to wait for MRI results, rushing to negative conclusions is not productive.