It is important to understand the general role of the left knee in the golf swing. Assuming you are a right handed golfer, the left knee (as well as the entire left side) provides the foundation to which the golfer "drives" all his power from the right to left side. When you generate as much power as Tiger the knee takes a tremendous amount of stress.
A good friend of mine is an esteemed researcher at Arizona State University, specifically her work focuses on golf performance. Debbie Crews Ketterling, Ph.D. is the author a book entitled Golf: Energy in Motion – It’s not about the ball; It’s about the possibilities!
One of the most common swing flaws I see, particularly in higher handicap golfers is "coming over the top". This occurs when the upper body controls the swing leaving the lower body behind and the club head is "thrown" outside towards the inside swing path.
