By Brendan Pierson

Dec 4 (Reuters) - The top U.S. patent appeals court has thrown out a $176 million award for healthcare company Covidien Plc in a dispute with a Johnson & Johnson subsidiary over surgical instruments.

Judge Sharon Prost of the U.S. Court of Appeals for the Federal Circuit in Washington, D.C., ruled on Thursday that Covidien's patent claims, which involve surgical cutting tools that use ultrasonic technology, were invalid.

Dublin-based Covidien in 2010 sued Ethicon Endo-Surgery Inc, a subsidiary of New Jersey's Johnson & Johnson, claiming it sold surgical tools that violated several patents issued in the 1990s. Last year a U.S. district judge awarded Covidien $176 million after a non-jury trial, and Ethicon appealed.

Prost said in Thursday's decision that the inventions described by Covidien's patent claims, which include using a curved blade instead of a straight one, were obvious in light of earlier technology.

Covidien said in a written statement that it was disappointed in the ruling and was considering its options.

Ethicon was not immediately available for comment.

Covidien agreed in June to a $43 billion takeover offer from Minnesota-based medical device maker Medtronic Inc. U.S. and European regulators approved the deal last month.

Shares of Covidien and Johnson & Johnson were both up 0.1 percent in afternoon trading.

Covidien, previously Tyco Healthcare Group LP, was spun off from security systems company Tyco International Ltd in 2007.

The case is Tyco Healthcare Group LP et al v. Ethicon Endo-Surgery Inc, U.S. Court of Appeals for the Federal Circuit, No. 2013-1324.

(Reporting by Brendan Pierson; Editing by Ted Botha and Lisa Von Ahn)