While the scheduled passenger flight was in the cruise at Flight Level (FL) 380, the Flight Crew received an initial clearance from Air Traffic Control (ATC) to descend to FL340. However, FL240 was set in the altitude window. During the descent ATC was queried regarding the cleared level and confirmation was obtained that FL340 was the cleared level as the aircraft was approaching FL340. The autopilot was disconnected and a manual control input was made to quickly level the aircraft. As a result of the rapid pitch change, a Cabin Crew Member (CCM), who was stationed in the aft galley area of the aircraft, sustained a broken ankle.
One Safety Recommendation is made to the Operator as a result of this Investigation.