BOSTON -- Sen. Edward M. Kennedy underwent surgery to repair a partially blocked artery in his neck on Oct. 12, which was discovered during an examination of a decades-old back injury.

Kennedy, 76, was released from Massachusetts General Hospital a day after the surgery, reported WCVB-TV in Boston.

The operation, performed by Dr. Richard Cambria, the hospital's chief of vascular surgery, took about an hour and was completed without complications.

"The surgery was routine, uneventful and successful," Cambria said.

The blockage was discovered in a regular MRI exam on his back on Oct. 4.

Kennedy's left carotid artery was more than 70 percent blocked. Though he had no symptoms, it posed the threat of a stroke. The problem was found during a routine examination of his back, which was injured in a 1964 airplane crash.

"Sen. Kennedy under went a carotid endarterectomy, which is a surgical procedure done through a small incision in the neck, where the blockage and plaque is actually removed," Cambria said.

"My understanding is it was a high-degree of narrowing -- severe narrowing -- in other words a large plaque, and that does carries an increasing risk of stroke. Once a diagnosis is made, particularly if it is a very severe narrowing, there is some degree of urgency involved," Newton- Wellesley Hospital Dr. David Brewster said.

Kennedy has been bothered by an aching back since a 1964 plane crash, which killed a pilot and one of Kennedy's aides. Then-Sen. Birch Bayh, D-Ind., who was traveling with Kennedy, pulled him from the wreckage but Kennedy suffered a back injury, punctured lung, broken ribs and internal bleeding.

Because of the persistent pain, the senator often leans on a wall or sits on a stool when he otherwise would be expected to stand for an extended period.

Kennedy is the lone surviving son in his storied political family. His eldest brother, Joseph, was killed in a World War II airplane crash, President John F. Kennedy was assassinated in 1963 and Robert was assassinated in 1968.

Kennedy, considered a liberal lion in the Senate, was re-elected in 2006. His term ends in 2013. The senator made a failed run for the presidency in 1980.