broken femur bone

I am a 39 year old female who was training for a marathon.  I hurt my knee running and within a few weeks it got worse.  I had a X-ray and they found nothing.  I had a MRI and they found a contusion in my bone marrow.  I woke up one morning and stretched my leg and my femur bone broke.  They put a 8 in plate in it.  Dr.'s don't know how it could just break.  What kind of tests do I need done?  Will I be able to run again?

[Michael L Gross, MD]

Most simply, this  sounds like the initial finding of a bone contusion, was actually a stress reaction or precursor to a stress fracture.  At some point, this went on to a stress fracture, with which trivial stress went on to become a full fracture.  
However there is a more worrisome explanation, an entity known as the female triad.  An unusual occurance during the 1990’s was that young, apparently healthy athletic females were appearing in their physicians offices with a history of repeated stress fractures to the lower extremity. In some cases x-rays revealed the early signs of bone loss, called osteoporosis.  Further investigation revealed that these females had a very low body fat levels, below 12%, and that they had temporarily lost their monthly period, a condition called amenorrhea.
This clinical picture began to expand and eventuallly included three things: an eating disorder, anorexia; a physiologic disorder, amenorrhea; and a radiographic finding, osteopenia, signaling osteoporosis. Together anorexia, amenorrhea and osteoporosis came to be called the Female Triad. While the short-term effects have been troubling, the long-term implications are frightening. The long-term tragedy of the Female Triad is that the amount of calcium bone deposition maxes out while a female is in her 30’s. Those that are osteoporotic in their 30’s, with natural progression, are destined for greater osteoporotic problems later in life than the "average" women.
There is no easy solution to this problem.  If this description feels familiar, an endocrine evaluation, psychological counseling, and nutritional guidance are all needed