Rich, great questions.From what I gather from what I have read elsewhere on this topic, the fractures from high accumulative dosages or prolonged biphosphonates therapy ( risk appears to be associated with 5 or more years of oral use) have a characteristics unlike other fractures of the femur as they are:
-nonstress related
-preceeded by a period of thigh pain prior to fracture
-transverse fracture with lateral pattern
-may heal more slowly, especially if still on biphos.
It seems at least with biphos. therapy, shorter duration ( less than 4-5 years) and concentration may be safest to prevent over-suppression of bone building matrix as the wash out of the drug is very prolonged with an EXPODENTIAL HALF LIFE, where half of the drug is only cleared at ten years.
Some other interesting stats :
http://www.orthosupersite.com/view.aspx?rid=41933