Firstly, I put the "pathological" in parentheses because I don't think it should be included in the translation as it is redundant. What process could produce bone fragility which is not pathological?

"Osteopathie" is a disease of bone, and "fragilisante" qualifies it as one of those diseases that weakens the bone. So, like Drmanu says, (if one were to translate this without thought), one would say it means "bone diseases inducing bone fragility".

However, if one looks at the whole sentence, one would then have to translate it "...one would have to assure that other causes of bone diseases inducing bone fragility have been ruled out".

That clearly is not the intention of the author. He wants to say "it is important to be assured that other causes of bone fragility have been ruled out". The term pathological is assumed. Now, most causes of bone fragility are not due to bone diseases per se, but are caused by extrinsic factors which affect the bone, such as hyperthyroidism, hyperparathyroidism, corticosteroid ingestion etc.
I think that the meaning is clear enough in French, even if it is not technically correct, but if you translate it, as is, into English, you get garbage. The author's intent is to caution the reader to rule out other intrinsic and EXTRINSIC causes of bone fragility.

So who am I to to change the text? I am a knowledgeable translator/editor whose job is to convey meaning. I understand the author's meaning because of my technical expertise.

http://edrv.endojournals.org/cgi/content/abstract/er.2006-00...