Two employees were changing out the skid steer attachment from a bucket to forks. The bucket did not fall free when the two retaining pins were removed due to the build up of dirt. The bucket was still lifted about six inches above the ground. The injured employee was standing near the bucket with his left hand resting on it, while another employee used a hammer on the opposite side to knock the dirt loose. The bucket fell approximately six inches and the injured employee's left hand was pinched between the bucket and fixed supports resulting in amputation of the middle and ring fingertips.