BOSTON — Boston Mayor Thomas Menino fractured the smaller of the two bones in his lower leg on Friday, the latest in a series of health issues that have dogged the city’s longest serving chief executive since the end of last year.

Spokeswoman Dorothy Joyce said 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.

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

It’s unclear how long Menino, 70, will be off his feet.

“He’s fine,” Joyce said. “It’s a very common, simple fracture and doctors thought it’s best to fix it rather than letting it heal on its own.”

The mayor was with his aides in the hospital Friday afternoon and his wife was expected to visit him later, Joyce said.

Menino recently announced he won’t seek re-election after nearly two decades in office.

He spent about six weeks at Brigham and Women’s Hospital, leaving the facility just in time for Christmas. He was admitted for treatment of a respiratory infection that developed during a vacation in Italy. While at the hospital he suffered complications including a compression fracture in a vertebra in his spine. Menino was also diagnosed with Type 2 diabetes.