During the cruise portion of a scheduled international passenger flight, a flight attendant incurred serious injury while trying to stow a beverage cart during an encounter with turbulence. The flight attendant stated, "…the cart as it often does, went to the side and not forward as I was trying to put it in its secured position. Unknown to me, when the cart went on [its] own route to the side and not forward it must have caused a whip lash." The flight attendant continued with her duties for the remainder of the flight, and sought medical attention after the flight landed at its scheduled destination. The flight attendant's injuries consisted of two fractured ribs. According to statements provided by the cockpit crew, they were unaware that anyone had been injured until several days after the conclusion of the flight. None recalled encountering any significant turbulence during the flight. Seven other flight attendants also provided written statements. Five of the flight attendants did not recall anything abnormal about the flight, one recalled encountering a "patch of rough air," and one recalled encountering an unexpected area of "severe turbulence." Due to the Safety Board's late notification of the event, flight data recorder information pertaining to the accident flight was not available. The exact time and location that the event took place could not be determined.