Avulsions of the tibial eminence are most frequently seen in high energy trauma such as a motor vehicle accidents, and in children where bone is pliable and gives way before the ACL tears. In this case, a young man in a motor vehicle collision sets up a reasonable scenario for this injury, which is actually quite well evaluated on the plain film images in this case. 

This case is courtesy of Eric White, MD, who generously shared it with me.