August 2006: Dr. Timothy Kuklo, a highly regarded spine specialist and West Point graduate, becomes a Medtronic consultant upon retiring from Walter Reed Army Medical Center.

August 2008: A study purportedly written by five doctors at Walter Reed is published by a British medical journal, The Journal of Bone and Joint Surgery. It claims the authors studied 138 soldiers injured in Iraq, some of whom were successfully treated with Medtronic's bone-growth product, Infuse. Shortly after publication, one of the "co-authors" contacts the Journal and Walter Reed and says he had not signed off on the study.

September 2008: Walter Reed initiates an investigation into the study.

March 2009: The journal retracts the study at the Army's request.

May 13, 2009: The New York Times publishes a story about the dispute. Medtronic says it was unaware of the Walter Reed study.

May 19, 2009: Sen. Charles Grassley, ranking Republican on the Senate Finance Committee, opens an investigation into the Kuklo matter.

May 21, 2009: Medtronic says it has suspended its consulting agreement with Kuklo until the controversy is resolved.

May 22, 2009: Kuklo takes a leave of absence from Washington University.

Week of June 7, 2009: Medtronic CEO Bill Hawkins says during a CNBC interview that Kuklo began consulting for the company in August 2006; Medtronic issues a clarification saying Kuklo was paid for training and education while at Walter Reed.

June 17, 2009: Responding to Grassley, Medtronic reveals it had paid Kuklo $851,000 directly and indirectly between 2001 and 2009.

June 23, 2009: Medtronic reveals in a securities filing that it has received a subpoena from the U.S. Department of Justice seeking information about the retracted study.

July 7, 2008: The Senate Committee on Armed Services asks the Army for information about Kuklo.

Source: Star Tribune research