Boston Mayor Thomas Menino has fractured the smaller of the two bones in his lower leg, the latest in a series of health issues that have dogged the city's longest serving chief executive.

Spokeswoman Dorothy Joyce says Menino twisted his ankle on his way to an event Friday morning. He went back to his office, applied ice to the ankle and called his doctor when it began to swell.

Joyce said an X-ray revealed the fracture. Doctors are keeping the mayor at Brigham & Women's Hospital and will perform surgery on the leg Saturday morning.

Joyce says it's unclear how long Menino will be off his feet. She says the fracture is common and doctors thought it best to repair it rather than letting it heal on its own.

Menino recently announced he won't seek re-election.