Boston Scientific (NYSE:BSX) used to be the big man on campus. It stormed the U.S. drug-eluting stent market, capturing more than half of Johnson & Johnson's (NYSE:JNJ) market share. But its market share slipped to 45% in the third quarter of last year after the launch of Medtronic's (NYSE:MDT) Endeavor and Abbott Labs' (NYSE:ABT) Xience V.

Going from a duopoly to a quadopoly will do that.

But Boston Scientific is getting back in the game. The medical device maker launched its new Taxus Liberte at the end of last year, and in the first quarter it clawed its way back to a 50% share of the U.S. drug-eluting stent market.

Its newest weapon may be small, but it could help the company regain a few more percentage points of the market. Yesterday the Food and Drug Administration approved Boston Scientific's Taxus Liberte Atom. The stent is smaller than the standard Liberte and can be used in the estimated 10% of patients who have small blood vessels that need stenting. Previously, those patients would just receive bare-metal stents, but Boston Scientific now has two stents -- the Liberte Atom and the older Express Atom -- that are approved for the smaller blood vessels.

The U.S. drug-eluting stent market had been fairly stable for many years; all Johnson & Johnson and Boston Scientific had to worry about were safety concerns. But the market is in flux and will likely remain that way for a while. By the time we figure out how doctors are going to split among the current offerings, the next-generation stents will be headed for the market. Johnson & Johnson is developing a stent with a bioabsorbable coating, as are Abbott and Boston Scientific. Stay tuned!

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.