The top after-market NASDAQ stock market losers are: PMC-Sierra, Thoratec, Amazon.com, Digital River, Amedisys, Werner Enterprises, Tessera Technologies, LTX-Credence, PSS World Medical, and Patterson-UTI Energy.

Shares of PMC-Sierra Inc. (PMCS) plunged 12.68 percent to $7.78 in the after-hours trading, following its lower-than-expected fourth quarter earnings. Adjusted profit was $34.58 million or 15 cents a share, down from $39.23 million or 17 cents a share last year. Revenue rose 14 percent to $159.25 million. Analysts had expected profit of 16 cents a share on revenue of $156.96 million. The company expects first quarter revenue of $150 million to $160 million, lower-than analysts forecast of $167.55 million.

Thoratec Corp. (THOR) stock plummeted 10.26 percent to $23.45 in the after-market trading, following its weak 2011 outlook. The company expects full year 2011 adjusted earnings of $1.35 to $1.45 a share and revenue of $410 million to $425 million, while Street predicts profit of $1.50 a share on revenue of $443.75 million.

Thoratec reported fourth quarter adjusted earnings from continuing operations of $18.1 million or 28 cents a share, up from $15.5 million or 24 cents a share last year. Revenue rose 20 percent to $97.61 million. Analysts had expected profit of 30 cents a share on revenue of $98.98 million.

Shares of Amazon.com Inc. (AMZN) dropped 9.38 percent to $167.15 in the after-hours session. Profit for fourth quarter was $416 million or 91 cents a share, up from $384 million or 85 cents a share last year. Sales rose 36 percent to $12.95 billion. Analysts had expected profit of 88 cents a share on revenue of $12.98 billion. The company expects first quarter sales of $9.1 billion to $9.9 billion, representing a growth of 28 percent to 39 percent over last year, while Street predicts $9.30 billion.

Digital River Inc. (DRIV) stock tumbled 8.48 percent to $32.50 in the after-market session, following its lower fourth quarter earnings and revenue. Adjusted profit was $11.7 million or 29 cents a share, down from $15.3 million or 40 cents a share last year. Revenue declined to $97.7 million from $104.9 million. Analysts had expected profit of 29 cents a share on revenue of $96.75 million.

Digital River expects first quarter adjusted earnings of 29 cents a share and revenue of $98 million, while Street predicts profit of 31 cents a share on revenue of $97.29 million. The company expects fiscal 2011 adjusted earnings to rise 19 percent from a revised $0.95 a share to $1.13 a share and revenue of $404 million, while Street predicts profit of $1.35 a share on revenue of $407.06 million.

Shares of Amedisys Inc. (AMED) fell 8.22 percent to $33.26 in the after-hours trading.

Werner Enterprises Inc. (WERN) stock declined 7.61 percent to $23.69 in the after-market trading.

Shares of Tessera Technologies Inc. (TSRA) decreased 5.70 percent to $20 in the after-hours session, following its announcement of a reduction of its Imaging & Optics segment employees that is expected to be up to 15 percent of its worldwide employee base. The company expects to incur severance and other related costs in conjunction with the planned workforce reduction of $2.5 million to $3.0 million, which it will recognize in the first quarter.

Tessera reported fourth quarter adjusted profit of $23.1 million or 44 cents a share, up from $16 million or 31 cents a share last year. Revenue rose 42 percent to $80.44 million. Analysts had expected profit of 27 cents a share on revenue of $77.83 million. The company expects first quarter revenue of $65 million to $68 million, while Street predicts $72.83 million.

LTX-Credence Corp. (LTXC) stock slid 5.09 percent to $8.40 in the after-market session.

Shares of PSS World Medical Inc. (PSSI) fell 5.04 percent to $23.14 in the after-hours trading.

Patterson-UTI Energy Inc. (PTEN) stock moved down 4.89 percent to $21.29 in the after-market trading. The company said it sold the stock of its electric wireline unit Universal Wireline, Inc. to Gray Wireline Services Inc. in a cash transaction for $25.5 million.

Except for inventory, the working capital of Universal Wireline was excluded from the sale and has been retained by a Patterson-UTI subsidiary. Expenses related to the sale of about $2.2 million will be reflected in results of discontinued operations for the fourth quarter of 2010. No other significant gain or loss is expected to result from this transaction.

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