How to treat muscle during a femur fracture?

Need more detail: If you mean how to you exercise the muscle, then you can do isometric quadriceps exercises, that are generally safe and reduce atrophy. Your limitations however are determined by the type, location, severity, and or type of surgical fix that was done. Because there are so many variables, you have to ask your surgeon for the proper recommendations.

Keep moving : Once the fracture is well fixed surgically it is good to keep all muscles moving as much as possible but must be careful to not over do it nad to limit wt bearing within the parameters set by your orthopedic surgeon ask your orthopedic surgeon about this and maybe physical therapy might be appropriate.