Due to the anatomy of the human ankle, when a person's foot hits the ground the resulting forces can be transferred up an individual's whole lower extremity in what are known as "obligatory motions/movements". The shape of the ankle joint forces the tibia (main lower leg bone) to either rotate inwards or outwards depending on the motion that the foot undergoes. The two main movements of the foot that are commonly focused on are "pronation" and "supination".
Pronation of the foot can generally be thought of occurring when a person's weight is bore more on the inside of the foot, and supination more on the outside. Due to the obligatory motions of the foot and ankle, pronation of the foot causes the tibia to turn inwards ("internal rotation"), while supination of the foot causes the tibia to turn outwards ("external rotation"). These coupled motions continue up the "kinetic chain," in this case the rest of the lower extremity. If the foot pronates, then the knee flexes and also bends inward in what is known as a "valgus" direction (think knock-knees). The femur (upper leg/thigh bone) also is forced to internally rotate at the hip joint. With supination it is the opposite, the knee extends, the knee bows outward ("varus" direction) and the femur externally rotates just like the tibia.
Because of this biomechanical connection between the foot, the hip and everything in-between, one should take into account what is occurring at the foot with any orthopedic problem that a person has involving the lower extremity. The opposite also holds true, one should always consider the hip as a potential factor when dealing with a problem involving the rest of the lower extremity, all the way down to the foot. Strength deficits of the hip muscles as well as structural abnormalities of the femur can both play a role in common orthopedic issues of the lower extremities such as plantar fascitis and knee pain.
Fortunately a thorough examination performed by a skilled physical therapist can determine the appropriate treatment to address these types of orthopedic problems. Whether it be therapeutic exercises, recommendation of appropriate footware, manual therapy and SASTM, electrophysical modalities (example: ultrasound), or a combination of different treatments, physical therapists are very capable of helping individuals return to their normal quality of life and function.
~Drew Nelson, PT, DPT