Surgeons are generally specialists in one particular area and possibly even specialists within that area (ie: only do knee replacements, etc.). Surgeons get better with experience, it's a skill, and different surgeries are different enough that experience doesn't transfer too much. There's also changes over time in best practices so skills degrade not just due to lack of recent experience. If I remember the best predictor of the outcome of your surgery is how many similar surgeries the doctor does per year.