Usually bones break because of extra force put on them, such as from falling or a car accident. In a pathologic fracture, the bone can break just by doing everyday things such as walking. The bone is weak because of the disease, so doing an everyday activity may be too much for it.
Osteoporosis is usually the cause of the pathologic fracture, but other bone diseases, including types of cancer, may be the reason.
When your bone breaks due to a pathologic fracture, surgery may be necessary to put the bone pieces where they need to be to heal.