femur
The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with the tibia and kneecap forming the knee joint. By most measures, the femur is the strongest & the longest bone in the human body.
As its a strong bone it takes a lot of force of broke it but if ones it's broken or damaged a bit you should immediately go to an orthopedic doctor for the treatment.