A medical-device company illegally tested bone cement during spinal surgery on about 200 patients, three of whom died on the operating table, U.S. prosecutors in Philadelphia charged Tuesday.

A lengthy indictment charges that West Chester-based Norian Corp. trained dozens of surgeons to conduct unofficial clinical tests of the product on humans, subverting Food and Drug Administration safeguards. The company is charged with conspiracy and 51 other felonies.

Prosecutors say the surgeries took place from 2002 to 2004 but ended after the third death. The product, Norian XR, was approved for use in the arm but not the spine, prosecutors said. The surgeries often involved older patients with compression fractures.

According to the indictment, the company's pilot studies showed the product could cause blood clots in humans, while pig research suggested such clots could move to the lungs.

The patients who died suffered severe hypotension, or low blood pressure, following injections of Norian, authorities said. The deaths occurred in California and Texas.

"None of the surgeons could rule out the Norian," said Special Agent Kim A. Rice of the FDA's Office of Criminal Investigations.

The company halted the physician training program after the deaths but did not recall the product, a move that would have alerted the FDA, authorities said. And officials from Norian's parent company lied about the testing when the FDA began investigating, prosecutors charged.

Norian is a subsidiary of Synthes North America, which is also based in West Chester and specializes in products to treat bone trauma. Synthes has its global headquarters in Switzerland.

In addition to the felony charges, Synthes Inc. is charged with 44 misdemeanors and four Synthes executives are charged with a single count each of shipping Norian XR in interstate commerce.

They are: Synthes North America President Michael D. Huggins, 51 of West Chester; Thomas B. Higgins, 52, of Berwyn, Pa., a Synthes senior vice president; Richard E. Bohner, 55, of Malvern, Pa., a Synthes vice president; and John J. Walsh, 46, of Coatesville, Pa., Synthes' director of regulatory and clinical affairs. It was not immediately clear whether they had lawyers, and a woman at the company said no comment was planned.

In a statement, Synthes said it planned to fight the charges and said Norian XR was approved by the FDA to treat bone defects "in the skeletal system." The company said it sold 200 units of the product, for $400,000, from 2002 to 2004.

"Synthes has fully cooperated with the government's investigation, which began in 2006, and believes that its marketing practices in connection with Norian XR were proper," the statement said.