Sometimes the devil really is in the details.

Investors already knew that Amgen's (NASDAQ:AMGN) osteoporosis treatment, denosumab, worked. They just didn't know how well. The biotech giant reported in July that the drug had passed its phase 3 trial, but only just released the detailed data at a medical conference.

Passing its phase 3 trial will help get denosumab on the market. But two big questions remain: how well it worked, and whether anyone will buy it, given the drug's plentiful rivals. Between GlaxoSmithKline's (NYSE:GSK) Boniva, Novartis' (NYSE:NVS) Reclast, Eli Lilly's (NYSE:LLY) Evista and Forteo, and generic versions of Merck's (NYSE:MRK) Fosamax, simply being better than a placebo is not enough. To gain market share, your drug must beat the competition.

The data presented at the American Society of Bone and Mineral Research showed that denosumab cut the risk of spinal fractures by 68%, and hip fractures by 40%, compared to placebo. However, that's pretty comparable to how Reclast performed. The hip fracture numbers weren't as good as Fosamax's 51% improvement, but Fosamax didn't improve spinal fractures nearly as well, either, so that's a wash.

To satisfy my scientific background, I need to tell you that comparing numbers between trials isn't very scientific, because different populations of patients were enrolled in each trial. But that caveat doesn't keep doctors and analysts from drawing such comparisons, as I just did.

Ultimately, denosumab's ability to make a dent in the market probably depends on which method of drug delivery patients and doctors prefer. Reclast is given via a 15-minute infusion once a year, while denosumab is injected twice a year, and Fosamax is a once-daily pill. There's no clear-cut winner there. Only time will tell which will win.

Investors seem to have liked what they saw -- Amgen was up 6% yesterday. Still, I have to wonder whether investors weren't just pumped up about any good news at all, given all of this week's turmoil.

Do you agree or disagree? Does Amgen have a new blockbuster drug, or a dud? Join more than 115,000 like-minded Fools on Motley Fool CAPS, pick Amgen to outperform or underperform, and tell everyone why, absolutely free.

Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. Eli Lilly and Glaxo are Income Investor recommendations. Try any of our Foolish newsletters today, free for 30 days. The Fool has a disclosure policy.