The femur is attached to the pelvis and knee cap, which makes it the longest bone in the body. The National Space Biomedical Research Institute states the average adult femur measures 20 inches and is more than 1 inch in width.
The femur connects to the pelvis socket, which creates the hip joint. This joint provides the entire body with stability, especially during moments of intense movement.
The front of the femur is shaped to support the patella, or kneecap. When a leg is extended, the grooves in the front of the femur allow the patella to safely move upward. When the knee is bent, the groove allows the patella to move downward. The movement of the patella supported by the femur enables efficiency of the leg muscles, according to Health Line.