The injured employee was assisting with hitching a trailer to a truck. The employee was working to engage the lunette ring on the trailer with the pintle hook on the truck. A mini-excavator began driving onto the rear of the trailer. The added weight caused the rear of the trailer to lower and the front to rise, creating a pinch point between the trailer and the truck. The employee s left thumb was caught in the latch mechanism of the pintle hook. The thumb tip was partially amputated and required surgery.