Is boniva (ibandronate) as likely to break a femur as fosomax?

No: Boniva (ibandronate) won't break anything. It's designed to help not to break bones. It works as well as fosamax, but is taken once monthly vs. Fosamax that is taken once weekly.

Not as likely....: ... But, atypical femoral fractures have been associated with all of the oral bisphoshonates, including boniva (ibandronate). The drug does not break the bone, but the effect of the drug on bone is to reduce the usual self-repair rate and the bone responds less well to stress. Some of my colleagues have collected a group of 120 of these fractures, and at least 85% of them were associated with fosamax.