A story reported that for wrong side surgery, that:

Risk appears to be highest among patients receiving orthopedic or podiatric surgery.

A report from a survey of orthopaedic surgeons and foot survey in 2010 found

In all, 41 of 310 respondents (13%) reported performing WSS at least once, with 4 surgeons (1%) reporting the occurrence twice in their careers; 70 of 310 (23%) surgeons reported that they had prepped the wrong surgical site, but the error was recognized prior to making an incision.

Even though its rare, there is a risk and every good surgeon has in place strategies to make sure that it does not happen. The American Academy of Orthopedic Surgeons has a sign your site campaign to have surgeons mark the site prior to starting the surgery. This have been reported to have positive effects.