What bone did i brake when i had a full leg cast on.i was hit by a car. the cast started at my toes up to my groin. ?

Most likely the femu: It is difficult to say for sure which bone without seeing an x-ray, but with your history of being hit by a car, it is most likely the femur which is the thigh bone. The other two possibilities are the tibia, which is the shin bone, and/or the fibula, which is the small bone on the outside of the leg next to the shin bone.