Why you might ask! Essentially a knot in the thigh pulls and shortens that very big muscle which in turn can twist or pull the entire body which invariably ends up putting strain on the lower back. Try it - tense up your quads (separately or together) and feel it pull on your lower back.
Now the release of those big knots is where acupuncture is especially quick and effective. If you don't believe me, come and visit me and find out - 50% off your first treatment if you quote this blog!!