An interesting question. I am not a surgeon, but I do practice medicine, and I have never heard of this. Also, when I was in medical school, I never saw a single surgeon use or discuss them. That said, I did find a few examples on the web. Perhaps they haven’t gained much traction because the few studies that have compared their use to stainless steel show no difference between obsidian and steel scalpels in terms of wound healing. I think your research shows (correctly) that they are not approved for human use, probably because sharp as they are, obsidian knives tend to be brittle (I really love that I linked to a sword discussion board), and no one wants broken shards of glass in a wound.