Democratic mayoral nominee Bob O'Connor is scheduled to undergo a total knee replacement on Monday, following what a spokesman characterized as a painful campaign.

The surgery is set to be performed by Anthony M. DiGioia III, director of the Institute for Computer Assisted Orthopaedic Surgery, at The Western Pennsylvania Hospital. A four-day post-operative hospital stay is anticipated, said Dick Skrinjar, spokesman for the O'Connor campaign.

O'Connor, now 60, said his left knee had been "bone on bone for 40 years," following a football injury he suffered at age 18. As a young man, he had cartilage removed from the knee, he said.

"It's been a pretty painful campaign for him," said Skrinjar. "He really disguised [the knee condition] really well. Only the inner circle knew about it."