Often times the arch over pronates and causes the arch to flex toward the ground. As a result of this condition, all other body parts follow - the knee joint flexes inward, the hip joint flexes downward, the lower back flexes side-to-side.
Over hundreds of step or hours of standing the unnatural movement causes irritation, fluid build-up, eventually a general ache is constantly felt and things begin to wear. Knee pain is associated with excessive side-to-side motion due to the arch not maintaining the joint in the neutral position. A well crafted custom orthotic supports the arch to minimize over-pronation thus minimizing excessive movement.
Uneven weight distribution causes lines of pressure. These may eventually lead to inflammation that can cause considerable pain. A well-crafted custom orthotic will spread out your weight evenly and will reduce pressure points. Once these points are minimized, the source of inflammation will have been eliminated allowing the body to heal. Connective tissue called Plantar Fascia may become infamed causing Plantar Fasciitis.
Computer scans identify your foot in two dimensions. This data is interpolated into three dimensions. This is NOT data from your foot. The ONLY way to accurately manufacture an orthotic from your foot is to gather three dimensional data.