The feet were designed to absorb shock with landing and then to become a propulsive mechanism. In order for this to occur, one will pronate with landing and then re supinate with push off. In order to accomplish this, it requires the bones in the foot, legs, and hips to rotate in and out with exact timing, trajectory and symmetry of motion.
Any changes that occur within these motions, for example to compensate for a joint that is not ready to bend at a certain time of gait, will cause strain some where in the kinetic chain (areas of movement through your body). The resultant lack of shock absorption can transfer to your back. In most cases, the back pain typically results from abnormal muscle pull caused by the abnormal compensations during the propulsive phase of gait. Long term, this can cause leg length discrepancies, etc. as well.
Realigning the foot to obtain equal timing trajectory and motion within the kinetic chain will typically reduce the back pain rather rapidly. I’ve seen patients that achieve relief as soon as they put their custom orthotics on!
Similar to back pain, knee pain results from abnormal pull about the knee or twisting of the knee. When we pronate and supinate, the tibial (leg bone) will twist in and out respectively. If the femur (thigh bone) is not aligning with the tibia, then strain on the knee joint can occur, resulting in knee pain.
Strain can also occur about the tendons and knee joint causing bursitis as well as IT band syndrome and patellofemoral pain. Realigning the feet with custom orthotics will typically aid in realigning the tibia femur motion at the knee joint, thus relieving pain and helping long term.
Again, abnormal biomechanics are usually the cause. If the pain is anterior in the hip, it can be as a result from arthritis in the hip. Addressing the cause of the excess pressures and motions within and on the hip will by realigning the feet typically results in reduction or elimination of pain.
NOTE: With any musculoskeletal condition, physical therapy through stretching, strengthening and other modalities, as needed, are usually helpful. However, I have found addressing the cause of these problems will aid in sometimes faster resolution of pain as well as longer term prevention of such. Address the cause and our bodies will heal.