Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of specialty hospital operator Select Medical Holdings (NYSE: SEM) jumped as much as 12% in intraday trading after the company announced estimated first-quarter results.

So what: For the first quarter, Select Medical expects total revenue between $685 million and $695 million and earnings per share between $0.21 and $0.22. At the midpoint of the ranges, the company would report 43% growth in per-share earnings on 18% revenue growth. The estimates also easily top Wall Street's expectations for $670 million in sales and EPS of $0.17.

Now what: The estimated first-quarter results come on the heels of the company's announced tender offer for $612 million of its outstanding debt. Pair the better-than-expected results with the potential for an improved balance sheet, and it's little wonder that investors are excited today. Currently trading at roughly 13 times expected 2011 earnings, Select Medical's shares look pretty reasonably priced as well.

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Fool contributor Matt Koppenheffer does not have a financial interest in any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or on his RSS feed. The Fool's disclosure policy prefers dividends over a sharp stick in the eye.