Often clients will present with a pelvis where one side is higher or rotated forward more than the other. Although this is often dismissed as a difference in leg lengths, true differences in leg lengths are rare. Typically, the cause is a muscle imbalance pulling on one side of the pelvis in relation to the other. This makes it appear that one leg is longer than the other. It also contributes to a rotated spine and back pain.
There are several muscles attaching to the front of the pelvis which can potentially alter pelvic alignment. They are the tensor fascia lata (TFL), rectus femoris, and sartorius muscles. Poor habits, i.e., standing asymmetrically, can cause one side of the pelvis to develop tighter muscles than the other side. This pulls that side of the pelvis forward and down, creating a rotated pelvis. Pelvic rotation can create height differences between the two hips. Another contributor could be an overly pronated (flat) foot. A pronated foot can functionally shorten a limb relative to the other leg. I'd say in about 85 percent of the cases I see, pelvic and knee pain is fixed by addressing the pelvic muscles, not the foot. If pain still persists after correcting hip and knee function, then I consider correcting the foot including foot orthoses as a last resort.