The S&P 500 skidded 3.9% to 1,091.76 on a shortened trading week last week, as uncertainty swept over the markets. Among the major catalysts last week, President Obama proposed imposing new limits on the size and activities of the nation's largest banks. China's decision to temper lending in order to tap the brakes on frothy growth also ignited intensive selling, as investors feared for the implications of the anemic global recovery.

Pops and drops
Here are the five biggest S&P 500 upticks and five biggest S&P 500 drops of last week (measured Friday close to Friday close):

Winners on the week:

Company

Percentage Gain on the Week

Intuitive Surgical (NASDAQ:ISRG)

10.3%

Huntington Bancshares (NASDAQ:HBAN)

9.6%

Zions Bancorp (NASDAQ:ZION)

8.6%

Comerica

8.4%

SUPERVALU (NYSE:SVU)

7.7%

Source: Capital IQ, a division of Standard & Poor's.

Losers on the week:

Company

Percentage Loss on the Week

Cliffs Natural Resources

(14.8%)

AK Steel (NYSE:AKS)

(14.7%)

Tenet Healthcare

(14.5%)

Alcoa (NYSE:AA)

(14.3%)

Massey Energy (NYSE:MEE)

(13.6%)

Source: Capital IQ, a division of Standard & Poor's.

A closer look
Despite last week's down market, Intuitive Surgical bucked the trend, surging after it posted robust fourth-quarter results that trumped analysts' expectations. The company reported a 54% increase in earnings per share, thanks to sales of the company's da Vinci surgical robot system and increases in its instruments and accessories revenue. Total sales jumped 40% from the same quarter last year. The company is forecasting sales to increase 25% in 2010, compared with 20% in 2009, as more customers purchase its lucrative da Vinci system. These quarterly results validate my colleague Brian Orelli's nomination of Intuitive as the top-performing stock of 2010.

Another bright spot was SUPERVALU, which made the S&P 500's biggest winners list for the second straight week. The grocery chain's new CEO bought shares of his company for the first time since assuming his current role in May. When insiders buy shares -- particularly CEOs -- it can be seen as a vote of confidence in the company's prospects. Also, last week, Standpoint Research initiated coverage on the company as a "buy." Last week's positive news came on the heels of better-than-expected fiscal third-quarter earnings and news that the company is mounting a turnaround plan.

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Fool contributor Jennifer Schonberger does not own shares of any of the companies mentioned in this article. You can follow her on Twitter. Intuitive Surgical is a Rule Breakers pick. The Motley Fool has a disclosure policy.