By no means an expert, but you may want to check the fore/aft/centering position of your saddle. You could be dominant in one leg, thus the joints in your "power leg" take most of the stress. This was my problem. I skateboarded for 20 years and my back just can't take the trauma anymore and I gravitated to the bike. I am left leg dominant just from pushing for so many years. My discovery was made by a running expert on the treadmill, of all places, and we've made small adjustments until and focus exercises until it was rectified. Hope this helps...