Barbara Bush will be on crutches for several weeks, nursing a broken leg suffered when she slammed into a tree while sledding with her grandchildren at Camp David, Md.

The 65-year-old first lady returned to the White House in a wheelchair Sunday after the accident.Mrs. Bush "was going down a hill that was very icy" on a plastic inner tube-type sled, spokeswoman Anna Perez said.

"She doesn't know why she didn't bail out. She just held on and the next thing she knew, there was the tree."

A presidential doctor, Lawrence Mohr, checked her cuts and bruises and sent her off by ambulance to a Hagerstown, Md., hospital, where X-rays revealed "a non-displaced fracture of the left fibula bone," the White House said.

The break was not severe enough to require a cast, but the doctors ordered the first lady not to put any weight on her left leg for several days.

Mrs. Bush had gone sledding with President Bush, several grandchildren and guests, including actor Arnold Schwarzenegger, at the retreat in Maryland's Catoctin Mountains.

Schwarzenegger, the former Mr. Universe who is head of the President's Council on Physical Fitness, was a weekend guest at Camp David with his wife, journalist Maria Shriver, and their baby daughter.

Doctors said the fracture would take five to six weeks to heal, Perez said, adding that Mrs. Bush was experiencing some pain but did not require medication.