This is an excerpt from BioMechanics Method for Corrective Exercise With Online Video, The by Justin Price.
The knee is the structure that bridges the feet and ankles and the lumbo-pelvic hip girdle. Therefore, any imbalances or malalignments in the structures above or below it will directly affect how the knee feels and functions. For example, during the single-leg squat assessment, you should have noticed that a valgus knee is usually accompanied by overpronation of the foot and ankle complex. This is because as the foot and ankle collapse toward the midline during overpronation, the lower leg also rotates inward excessively, pulling the knee into a valgus position. This movement of the knee also causes the thighbone to rotate inward, affecting the position of the hip socket (where the upper leg articulates with the pelvis). Because of this change in position of the upper leg and hip socket, the pelvis shifts out of alignment by rotating down and forward. This change in position of the pelvis causes the lower back to arch excessively (see figure 3.9) (Kendall, McCreary, and Provance 2005; Price and Bratcher 2010).