The S&P 500 Index (SNPINDEX:^GSPC) is on a tear this year, having risen 7.34% after just 33 trading days. It's at a five-year high, and mathematically speaking, its current trajectory is setting it up for 72% annual gains. Will that happen? Fool, I don't know, but I do know that today, a handful of stocks did their best to thwart the market's momentum. Here are today's three worst performers.

Our first laggard today is Allegheny Technologies (NYSE:ATI), which lost 3.5%. Its miserable day makes sense, since the specialty metals producer is sensitive to the price points of, well, metals. Those generally fell today, sending Allegheny shares down with them. It didn't help that Zacks Equity Research also added the company to its "strong sell" list on Friday.

Alexion Pharmaceuticals (NASDAQ:ALXN), a biotech with an interesting business model centered around treating extremely rare, severe diseases, was the second notable decliner of the day, falling 3%. Alexion has been on a steady and unforgiving slide since reporting fourth-quarter results last Thursday, falling nearly 5% that day, nearly 2% Friday, and a little more than 3% today. 

Rounding out the underperformers of the day is the medical devices company Medtronic (NYSE:MDT), falling 2.8% after disclosing quarterly results in the morning. The $46 billion company with a 2.2% dividend grew earnings almost 6% in the fourth quarter, but a weakening European environment was enough to disappoint. The continent accounts for a fourth of Medtronic's business, and the struggles there accounted for the CEO calling the quarter "challenging," in the earnings call. The higher-than-expected net income came from a tax credit that some analysts had failed to incorporate in their models.