Chicago First Lady Maggie Daley had surgery Tuesday to replace the metal rod in her right leg that's been causing her pain, the mayor's office said.
She's said to be resting comfortably.
"The surgery went well. She was in good spirits when she went in," said Dr. Merk, who also is an associate professor of Orthopedic Surgery at the Feinberg School of Medicine at Northwestern University.
"We needed to re-stabilize the femur by replacing the metal rod," said Merk in a written statement. "We hope and expect that this will result in a decrease in much of the pain she had been experiencing in recent months."
Her primary physician, Dr. Steve Rosen, stressed that the pain should not be viewed as a progression of her cancer.
Daley has been at Northwestern Memorial Hospital since early Saturday morning. Her private driver took her there just hours after she and the mayor, Richard Daley, attended an event at the Art Institute of Chicago.
She's expected to remain there for three to five days. The physical therapy she begins in the hospital will need to be continued at home, the mayor's office said.
Maggie Daley was first diagnosed with cancer in 2002 and in July 2006 had surgery to remove a tumor in her right breast.
A biopsy on a bone lesion in her spine was done at Northwestern Memorial Hospital in April of last year. The titanium rod that's been giving her discomfort was inserted into her right leg a month later.
The First Lady was last hospitalized in October while in Washington, D.C. to accept a leadership award. She also had an unexpected outpatient visit to Northwestern in January after experiencing "flu-like symptoms."