Knee pain is commonly caused by an issue with the hips and / or the feet.  The knees are a hinge joint so it is designed to flex and extend (unlike the shoulder joint).  It also allows a few degrees of internal and external rotation but this movement that can be very harmful.  A healthy knee is one that is perfectly aligned at all times and problems arise when this is not the case.  An imbalance of weak vs tight muscles originated from the hips will disrupt knee alignment causing pain and eventually premature wear and tear.  Similarly, overpronation (when arches of the foot drops inwards or downwards when walking) and oversupination (excessive weight placed on the outside of the foot while walking) will also disrupt the knee alignment.