The femur is the bone the largest bone in your body and also one of the strongest bones. It is a vital support system for your entire body and bears the majority of weight and pressure. It is the only bone in the upper portion of your leg and is covered by mostly muscle. Being covered by muscle makes it one of the strongest areas of your body but, it causes complications if something goes wrong. If someone were to fracture their femur, completely, then the strong muscles of the quadriceps, hamstrings, and many others would pull in the separated parts of your bone. This would not only be extremely painful but extremely dangerous at the same time. See, along the femur runs a vital artery called the femoral artery. It supplies the legs with oxygenated blood to keep muscles active. When the femur is broken the muscles pulling on the bone will cause this artery to break. This can result in serious bleeding and can even be fatal.