However, sometimes, a bone might look as if it is close to breaking. So, to prevent this, doctors sometimes recommend surgery that reinforces the bone by placing a thin steel rod or other kind of metal support in it.
Rush orthopedic surgeon Dr. Steven Gitelis explained to ABC7 how it works.
"We frequently will use a rod to reinforce the bone. The rod goes down the center of the bone; it's a very strong metal rod. The bone is a hollow tube. So, we thread it down there to make the bone strong again. We put these locking screws through the rod," Gitelis said. "And that further strengthens the bone."
Doctors say it is much easier to keep a damaged bone from breaking than to try and repair it after it has broken.
Friday's surgery does not mean Mrs. Daley's cancer is progressing. It is a common procedure often used to prevent broken bones.
Mrs. Daley has been in a wheelchair or on crutches since December while undergoing radiation treatment for her leg tumor. The hope is she will soon be able to walk on her own again.
The first lady has been battling metastatic breast cancer for eight years.
She has already tripled the average life expectancy for patients diagnosed with this stage of the disease.