Two employees were hooking up a hydro excavation trailer to clean out water troughs. The injured employee was guiding employee 2 while she was backing up the truck to the trailer. The injured employee then began lowering the jack of the trailer to connect the trailer to the ball hitch on the truck. The trailer would not come down onto the ball hitch. The injured employee was manually adjusting the trailer when it came down and caught fingers on his left hand between the trailer s tongue and the ball hitch resulting in fractures.