Looking at the benefits of the using poles, below is a quote on the most reported study...
"The primary benefit that has popularized the use of hiking poles is their ability to absorb impact, lessening the strain on the knees and legs. In a 1981 study, Dr. G. Neureuther found that a hiking pole can absorb up to 20 percent of the strain off of the opposite leg. The hiking pole is able to do this by redistributing impact onto the arms and shoulders, alleviating some of the impact on the legs when compared with hiking with no poles at all. A 1999 study in "The Journal of Sports Sciences" indicated that hiking poles can relieve up to 25 percent of compressive force from the knees when descending hills." (from Trail.com)
This study on this links goes into a bit more detail on the anatomical side of things.
www.northumbria.ac.uk/browse/ne/uninews/hikerspoles